Chemistry Segment 2 Study Guide
By: Lexi Pelton
Module 5
Matter exists in 4 phases. Solid, Liquid, Gas, and Plasma.
· Phases: A distinct form of matter in which all chemical and
physical properties are identical for a given sample, such as
solid, liquid, and gas.
· Solid: State or phase of matter that has a definite shape and
volume
· Liquid: State or phase of matter that has an indefinite shape
and a definite volume.
· Gas: State or phase of matter that has an indefinite shape and
an indefinite volume.
· Plasma: The state or phase of matter in which the electrons
have been separated from the atoms, often called ionized gas.
the phase of matter is considered a physical property because a
change in a substance’s phase does not change the chemical
properties or identity of the substance. The phases of matter are
determined by the kinetic energy of the particles and the
attractive forces between the particles. Remember that there are
attractions between particles, called intermolecular forces. The
effects of the motion of the particles on these attractions
determines the arrangement of the particles in a sample of
matter.
TYPES OF PHASE CHANGES:
· Melting: process of a solid transforming into a liquid when a
heat is added kinetic energy increases
· Melting Point: the temperature at which a given substance
melts
· Freezing: process of transforming a liquid to a solid by the
removal of heat, reverse of the melting process
· Freezing point: the temperature at which a given substance
transforms from a liquid to a solid
· Evaporating: Process of turning a liquid to a gas
· Vapor: Means the same thing as evaporation. In fact, the two
words are related. The process of becoming a gas can also be called
vaporization.
· Boiling: This process occurs when the temp is high enough,
evaporation occurs from within the liquid
· Boiling Point: temperature at which a substance boils.
** Boiling point of pure water is 100° C
· Condensing: The opposite of the evaporation process; the
process of a gas transforming into a liquid
· Condensation point: temperature at which the phase change
condensation occurs.
· Same temp as the substances boiling point.
REVIEW:
Heating and cooling curves ( lesson 05.02)
GAS LAWS:
Physical Characteristics and Variable
Typical Units
Volume (V)
liters (L)
Pressure (P)
Atmospheres (atm)
Temperature (T)
Kelvin (K)
Number of particles (n)
Moles (mol)
Ideal gas constant, R
0.082 L * atm / K mol
You have already seen that scientists use moles, temperature,
and volume to measure matter. Another measurement, pressure, is
also necessary for describing a sample of gas. Pressure is defined
as the force per area on a surface.The SI unit of pressure is the
Pascal (Pa), which is defined as one newton per square
meter(N/m2).However, chemists most often use units of atmospheres
(atm) or millimeters of mercury (mm Hg) to measure pressure.
(Millimeters of mercury are also known as torr, in honor of
Evangelista Toricelli, the inventor of the mercury barometer.)
Units of Pressure
1 atmosphere (atm)
= 760 mm Hg
= 760 torr
= 101.3 kilopascals (kPa)
When you want to convert from Celsius to Kelvin K= 273.15 +
oC
When you want to convert Kelvin to Celsius oC= K-273.15
NATURE OF GASSES:
· Low Density
The density of a substance in the gas phase is about 1/1,000 the
density of the same substance as a liquid because the gas particles
spread out so much farther from each other than they do as a
liquid.
· Compressibility
When enough pressure is applied, gases can be compressed to a
smaller volume because there is so much space between the
particles. With enough pressure, a gas can sometimes be compressed
to a volume thousands of times smaller than its initial volume.
· Expansion
Gases spread out to fill the entire container in which they are
enclosed because the gas particles are moving in all directions
with negligible attractive forces between them. This means that a
gas transferred from a 2-liter container to a 4-liter container
will expand, or spread out, to fill the entire 4-liter
container.
· Diffusion
Have you ever opened a bottle of cologne or ammonia on one end
of the room and somebody nearby commented on the smell just moments
later? Because of their high kinetic energy and random motion, gas
particles can spread out and mix with each other without being
stirred. The scent of ammonia travels through a room as its gas
particles mix with the particles of air.
· Fluidity
Gas particles are able to easily glide, or flow, past each other
because the attractive forces between them are negligible. The term
fluid is sometimes used to describe both liquids and gases because
of their ability to flow.
REVIEW THE KINETIC MOLECULAR THEORY OF GASSES (found at the
bottom of lesson 05.03)
4 Gas Laws:
1. Gay-Lussac’s Law:
2. Avogadro’s Law
3. Charles’s Law
4. Boyle’s Law
Gas Calculations:
Ideal Gas Law: A model gas that conforms perfectly to all of the
assumptions of the kinetic theory:
PV = nRT
R = 0.0821
Standard Temperature and Pressure
To aid in the comparisons of volumes or moles of gases,
scientists have agreed upon conditions known as standard
temperature and pressure, commonly abbreviated STP. The conditions
of standard temperature and pressure are exactly one atmosphere
pressure and 0°C (273.15 Kelvin).
Avogadro’s principle states that equal volumes of gases at the
same temperature and pressure contain equal numbers of particles.
At standard temperature and pressure (STP), one mole of any gas
occupies a volume of 22.4 liters. This mole-to-volume relationship
can be used as conversion factor in calculations pertaining to
measurements and reactions conducted at STP (1 atmosphere and
273.15 Kelvin).
Standard temperature and pressure
(STP)
1 standard temperature
0°C
1 standard temperature
273 K
1 standard pressure
1 atm
1 standard pressure
760 torr
1 standard pressure
14.7 psi
Diffusion: The gradual mixing of two gases because of the
spontaneous, random motion of their particles.
Effusion: The movement of gas particles through a small opening
in the container wall due to the pressure and particle movement
inside the container.
Graham's Law
This equation shows that the rate at which two different gases
(A and B) effuse from the same container is dependent on their
molar masses. Notice that in the equation the molar mass of A is
diagonal from the rate of A. Also notice that to actually calculate
and compare the rates of effusion, the square root of each
molar mass must be taken
Graham’s law can be applied in a variety of ways:
All matter can be classified into two categories: pure
substances and mixtures.
Mixture: A combination of two or more substances, each retaining
its individual composition and properties.
Mixtures vs. Compounds
There is an important difference between the way atoms combine
to form compounds and the way particles come together to form
mixtures.
When a compound is formed, it has different chemical and
physical properties than the pure elements it is made of, and it
can only be separated by a chemical change.
In a mixture, the individual substances retain their own
properties and can be separated easily by physical means. Refer to
the table below to see a comparison of compounds and mixtures
Heterogeneous Mixture: A mixture in which the composition and
properties are not uniform throughout the mixture.
Homogeneous Mixture: A mixture in which the composition and
properties are uniform, or the same, through-out the mixture.
Separating Mixtures:
1. Filtration
2. Evaporation
3. Simple Distillation
4. Chromatography
Solvent: In a solution, the substance that is in a greater
quantity; the dissolving medium.
Solute: In a solution, the substance that is in a lower
quantity; the substance being dissolved.
Saturated Solution: A solution containing the maximum amount of
solute able to be dissolved under the given conditions
Unsaturated Solution: A solution containing less solute than a
saturated solution under the given conditions
Colligative Property: A property of a solvent that depends on
the number of solute particles dissolved in it, but not on the
identity or nature of those solute particles
Vapor Pressure: The pressure exerted by the vapor particles that
evaporate from a liquid (or solid).
Molality: The concentration of a solution in moles of solute per
kilogram of solvent.
Molality (m) =
Module 6
Heat: The transfer of thermal energy from one substance to
another due to the temperature difference between the two
substances
Isolated System:
In an isolated system, neither matter nor energy is permitted to
exchange with the surroundings. This means that the total amount of
energy and matter contained in an isolated system will remain
constant, because energy and matter cannot enter or leave.
Our universe is an example of an isolated system. Scientists
theorize that the total amount of matter and energy remain constant
within the universe and cannot be exchanged with any
surroundings.
There are not many examples of true isolated systems, because it
can be difficult to completely block the exchange of energy between
a system and its surroundings, but some systems come closer than
others. Using insulated containers, such as coolers and foam cups,
helps to minimize the amount of heat flow between system and
surroundings.
Closed System:
In a closed system, energy can enter or leave the system but
matter cannot.
Earth is an example of a closed system. The outer edge of the
atmosphere acts as a boundary between the system, Earth, and its
surroundings. Matter does not ordinarily enter or leave the system,
except for the occasional meteorite or space shuttle, but energy is
freely transferred between Earth and its surroundings.
Chemists can use glassware, such as flasks and beakers, to
contain matter but allow energy to be exchanged. Light and heat can
pass through the glass in either direction, making sealed glass
containers another example of a closed system.
Open System:
In an open system, both matter and energy are exchanged freely
between the system and the surroundings.
Your body is an example of an open system. Matter and energy
both enter and leave your body throughout the day. These exchanges
are important to keep your body functioning properly.
When reactions occur in unsealed containers, matter and energy
are both able to be exchanged freely between the system and
surroundings. When vinegar and baking soda react together in an
open container, the gaseous product escapes to the surrounding air
as heat flows out of the container.
Thermochemistry: study of the changes in energy that accompany
chemical reactions and physical changes.
Endothermic Process: A chemical or physical change that absorbs
energy from the surroundings.
Exothermic Process: A chemical or physical change that releases
energy to the surroundings.
06.02 Review energy diagrams.
Specific Heat Capacity: The quantity of heat required to raise
the temperature of one gram of the substance by one degree
Celsius.
J/(°C * g)
The energy gained or lost is called enthalpy which is
represented by the letter, q.
q = m × c × Δt
q: The q represents the heat gained or lost by the system, in
joules.
m: The m in this equation represents the mass of the sample,
measured in grams.
c: The c represents the specific heat capacity of the substance
being heated or cooled. The unit for specific heat capacity is
joules per gram per degree Celsius.
Δt: Delta t (Δt) represents the change in temperature, in
degrees Celsius, when a substance gains or loses energy. The change
in temperature can be determined by subtracting the initial
temperature from the final temperature of the substance (tf –
ti).
Enthalpy Change
The enthalpy change of a system is equal to the energy flow of
heat between the system and its surroundings when the pressure
remains constant. The symbol for enthalpy is represented by the
symbol ΔH.
The sign on the enthalpy change value can be either negative or
positive. The sign represents the direction of the heat flow from
the perspective of the system, qsystem to the surroundings,
qsurroundings.
A negative enthalpy change value means that energy was lost by
qsystem to the qsurroundings. This is called an exothermic
process.
A positive enthalpy change value means that the energy is
absorbed from qsurroundings by qsystem. This is called an
endothermic process.
Below is are two interactives that explains this process.
REVIEW 06.04 ENTROPY AND ENTHALPY IN DEPTH
Free Energy
As we have seen, entropy, enthalpy, and temperature all have an
effect on the spontaneity of a chemical process. These properties
can be combined in an equation that helps determine if a physical
or chemical change is spontaneous at a given temperature.
ΔG = ΔH − (T × ΔS)
Collision Theory
Chemists believe that for compounds, atoms, or ions to react
successfully, the particles must collide together. This is the
basis for a scientific theory known simply as the collision
theory.
This theory is based on the idea that the rate of a reaction is
determined by the number of successful collisions that occur over a
given amount of time. A successful collision is one that results in
the making of the product(s).
Two factors—sufficient energy and correct orientation—must be
true for a given collision to successfully result in the production
of products. Both factors must be true for a given collision for it
to go to completion and form the products
Sufficient Energy
The collision between reactants must have enough energy for the
reactants’ valence energy levels to penetrate each other. This
interaction between valence energy levels allows the electrons to
rearrange to form new bonds.
If a collision between two reactants does not have enough
energy, the collision will not be able to produce the products.
Energy Distribution
We can use a graph like the one shown to represent the
distribution of energy within a sample of particles at a given
temperature.
This general curve, called a Maxwell-Boltzmann distribution,
shows us that the majority of the particles have moderate amounts
of energy, near the average kinetic energy of the sample, while
some particles have energy higher or lower than that average
value.
Remember that for a reaction to happen particles must collide
with energy equal to or greater than the activation energy for the
reaction.
That activation energy requirement can be marked on the diagram
to show us the amount of a given sample that has the possibility of
meeting this energy requirement in a collision.
Correct Orientation
When reactants come in contact with each other during their
random movement, the orientation of their collision will determine
if the collision is successful. The atoms from each reactant that
will bond together to form the new products must come in contact
with each other if a bond is going to form between them.
The more complex a reaction is, the slower the rate of the
reaction. For example, if more than two reactants need to collide
together at the same time with correct orientation the reaction
time would be slow.
For the reaction between ethene (CH2CH2) and hydrogen chloride
(HCl) to occur, the double bond between the carbon atoms in ethene
must be broken.
The double bond is converted to a single bond, allowing the
carbon atoms to each bond with one of the atoms from the hydrogen
chloride.
REVIEW SLIDES AT THE BOTTOM OF LESSON 06.05
Module 7
When chemists refer to an acid, they are often discussing a
compound that donates, or gives off, a hydrogen ion when dissolving
in water or reacting with another substance.
There are three commonly accepted chemical definitions of acids,
but we will focus on this definition as a hydrogen donor, called
the Brønsted-Lowry definition.
Although most acids are molecular compounds, their strong
polarity allows the polar water molecules to remove one or more
hydrogen ions from the molecule, leaving behind a negative ion.
If the acid is dissolved in water, the positive hydrogen ions
bond to water molecules to form hydronium ions (H3O +). In this
course, whenever we discuss hydrogen ions in an aqueous solution,
we can assume that they will bond with the water molecules to form
hydronium ions. This means that the two ions, H+ and H3O+, can be
used interchangeably when discussing acidic solutions.
Another common definition of an acid, the Arrhenius definition,
describes acids as any substance that increases the hydronium ion
concentration of a solution when it is dissolved in water.
Strong Acids
A strong acid is an acid that ionizes close to 100 percent in an
aqueous solution. This makes it a strong electrolyte because of the
greater concentration of ions in solution, and also means that the
concentration of the solution indicates the concentration of
hydrogen or hydronium ions in the solution.
Examples:
· Hydrochloric acid:
HCl →
H+ + Cl-
· Nitric acid:
HNO3
→ H+ + NO3-
· Sulfuric acid:
H2SO4
→ H+ + HSO4-
· Perchloric acid:
HClO4
→ H+ + ClO4-
· Hydrobromic acid:
HBr →
H+ + Br-
· Hydroiodic
acid: HI
→ H+ + I-
Weak Acids
Weak acids vary in their degree of ionization in an aqueous
solution, but it is often less than 50 percent. Weak acids are weak
electrolytes because there are fewer ions in solution at a given
concentration. It is important to remember that a given
concentration of a weak acid does not indicate the concentration of
hydrogen or hydronium ions in the solution.
Examples:
· Hydrofluoric
acid:
HF H+ + F-
· Phosphoric
acid: H3PO4
H+ + H2PO4-
· Carbonic acid:
H2CO3
H+ + HCO3-
· Acetic acid:
CH3COOH
H+ + CH3COO-
· Hydrocyanic acid (Hydrogen cyanide): HCN
H+ + CN-
Acid Anhydrides
Most acids contain hydrogen ions that break off from the
compound when it dissolves in water, as shown in many of the
previous examples. However, some acids do not contain hydrogen
ions.
These compounds, called acid anhydrides, increase the hydrogen
ion concentration of a solution by reacting with water molecules.
For example, carbon dioxide does not have any hydrogen in its
formula, but it creates carbonic acid when it is dissolved in
water. CO2 and H2O react to form the compound H2CO3. Once it is
formed, some of the carbonic acid acts as an acid by giving off
hydrogen ions to water in the solution.
H2O + CO2 → H2CO3
H2CO3 + H2O H3O+ + HCO3-
You may not have realized it, but you probably have several
substances around your house that would be categorized as bases.
Bases are excellent cleaning agents because they react with oils
and fats to make them more water-soluble, so you will notice that
many of the common bases on our list are found in cleaning
products.
Strong Bases
Strong bases ionize close to 100 percent when dissolved in
water, while weak bases ionize much less.
Metal hydroxides made from metals of groups one and two in the
periodic table are usually considered strong bases.
Examples:
· Sodium hydroxide
NaOH → Na+ + OH-
· Potassium hydroxide KOH → K+ + OH-
· Lithium hydroxide
LiOH → Li+ +
OH-
· Calcium hydroxide
Ca(OH)2 → Ca2+ + 2
OH-
Weak Bases
Examples:
·
Ammonia NH3
+ H2O → NH4+ + OH-
·
Pyridine C5H5N
+ H2O → HC5H5N+ + OH-
NaOH + H2O → Na+ + OH− + H2O
When a strong base like sodium hydroxide is dissolved, large
amounts of heat are released because the process is exothermic.
READ THROUGH 07.02
Many of the solutions that you encounter every day can be
categorized as acidic or basic. Use the pH paper provided to test
the pH value of some common substances. Substances with pH values
greater than 7 are basic, equal to 7 are neutral, and less than 7
are acidic. Record your findings in your notebook.
In addition to describing a solution as acidic, basic, or
neutral, scientists use numerical values to express the acidity of
a solution in more detail. Because the concentrations of hydronium
and hydroxide ions in a solution can vary greatly, chemists use
values called pH to conveniently express a solution’s hydronium ion
concentration.
The letters pH stand for the French words pouvoir hydrogène,
meaning “hydrogen power.” The pH scale is a numeric scale used to
indicate the hydronium ion concentration of a solution. The pH of a
solution is determined by calculating the negative base-10
logarithm of the hydronium ion concentration (in molarity).
pH of a Solution
pH= -log
Brackets are used to represent concentration in molarity.
According to the Brønsted-Lowry definition of acids and bases,
acids increase the concentration of hydronium ions in a solution by
donating hydrogen ions, while bases decrease the concentration of
hydronium ions by accepting hydrogen ions. This means that the
acidic or basic nature of a substance can both be measured and
described by its hydrogen ion, or hydronium ion, concentration.
This is why pH values can be used to describe acidic and basic
solutions, even though the values are calculated using the
concentration of hydronium ions.
The range of pH values of aqueous solutions generally falls
between 0 and 14, which is a more reasonable range for comparison
than the possible range of concentrations. The pH scale and its
values are dependent on temperature, so we will be comparing and
calculating pH values at 25 degrees Celsius.
The pH of a neutral solution, when the concentrations of
hydroxide and hydronium ions are equal, at 25°C is 7.0. When the
amount of hydronium ions is greater than the amount of hydroxide
ions in the solution, the solution is acidic and will have a pH
value that is lower than 7.0. In a basic solution, the amount of
hydroxide ions is greater than the amount of hydronium ions, and
the pH will be greater than 7.0.
BASE:
REVIEW SLIDES AT BOTTOM OF LESSON 07.03 IMPORTANT MATH
CONCEPTS
Dynamic equilibrium is a state of balance in which the forward
and the reverse reactions continue to occur, but the rates of the
forward and the reverse reactions are equal. All reactions have the
potential to reach equilibrium if they occur in a closed
system.
Dynamic equilibrium also occurs when physical changes take
place. When water is sealed in a flask, equilibrium will eventually
be reached between the evaporation and the condensation processes.
The faster-moving molecules in the liquid will escape as vapor,
while the slower-moving vapor molecules will condense back into a
liquid
Science is based largely on experimental investigations, and the
description of equilibrium systems is no different. In 1864, two
Norwegian chemists, Cato Guldberg and Peter Waage, used data and
observations from numerous reaction systems to propose the law of
mass action to describe the equilibrium condition.
Let’s examine the basic concepts of the law of mass action.
Consider the following general reversible reaction. In this
example, w moles of A react with x moles of B to produce y moles of
C and z moles of D in the forward reaction (w, x, y, and z are
coefficients, A and B are reactants in the forward reaction, and C
and D are products of the forward reaction).
wA + xB yC + zD
At equilibrium, the concentrations of each substance in the
system can be plugged into the equation below. The law of mass
action proposes that, for a reaction at a given temperature, this
equation can be used to relate the equilibrium concentrations of
the substances in the system to the reaction’s equilibrium constant
(K).
Remember that brackets are used to represent concentration in
molarity (M).
The value of a system's equilibrium constant (K) is constant at
a given temperature, regardless of the initial amounts of the
reactants and the products introduced into the system. Although
there is only one value for the equilibrium constant for a system
at a given temperature, there are infinite combinations of
equilibrium concentrations of the reactants and the products within
the system.
It is important for chemists to understand the factors that can
influence the position of a chemical equilibrium. For example, when
a chemical is being manufactured, the chemical engineers in charge
of production should choose conditions that will result in the
greatest amount of products that can be made under reasonable
conditions. This means they will choose conditions that move the
equilibrium position farther to the right.
We can predict the effects of changes in concentration,
temperature, and pressure on a system at equilibrium by using Le
Châtelier’s principle
Le Châtelier’s Principle: If a change is imposed on a system at
equilibrium, the position of the equilibrium will shift in a
direction that helps to reduce the effect of that change.. This
principle, proposed by the French chemist Henri Louis Le
Châtelier’s in 1888, states that if a change is imposed on a system
at equilibrium, the position of the equilibrium will shift in the
direction that tends to reduce the impact of that change. This
statement is a simplification of what really happens when a change
is imposed on a system, but it works well to help us make
qualitative predictions.
There are four possible scenarios that can be produced by a
change, or stress, to an equilibrium system:
1. Increasing the rate of the forward reaction will cause the
system to shift to the right to reach a new equilibrium.
2. Increasing the rate of the reverse reaction will cause the
system to shift to the left to reach a new equilibrium.
3. Decreasing the rate of the forward reaction will cause the
system to shift to the left to reach a new equilibrium.
4. Decreasing the rate of the reverse reaction will cause the
system to shift to the right to reach a new equilibrium.
REVIEW 07.05
07.06 Oxidation and Reduction: Overview—Text Version
Did you ever wonder what causes copper, like that in pennies and
in the Statue of Liberty, to turn green?
This type of reaction involves the exchange of electrons from
one substance to another. We have seen that many important
compounds are ionic, and ions are atoms that have gained or lost
electrons.
Sodium chloride, for example, can be formed by the reaction of
sodium metal with chlorine gas:
Na (s) + Cl2 (g) → 2 NaCl (s)
In this reaction, neutral sodium atoms react with neutral,
diatomic chlorine molecules to form the ionic compound sodium
chloride, which contains Na+ ions and Cl- ions.
Reactions like this one, where one or more electrons are
transferred from one particle to another are called oxidation-
reduction reactions, or redox reactions for short.
Oxidation
Oxidation is defined as the loss of electrons in a chemical
reaction.
In the reaction of sodium and chlorine, neutral sodium was
oxidized when it lost an electron to chlorine to make a positive
Na+ ion.
This term got its name because many metals lose electrons when
they react with oxygen to make an ionic metal oxide compound.
Gaining oxygen (after a loss of electrons) is where this term got
its name, “oxidized.”
Reduction
Reduction is defined as the gain of electrons in a chemical
reaction.
In the reaction above, neutral chlorine got reduced when it
gained electrons from the sodium to make a negative Cl- ion.
When an atom or particle gains a negative electron, its overall
charge is lowered, or “reduced.” This is where this term comes
from.
You Can’t Have One without the Other
Oxidation and reduction go hand in hand. One substance cannot be
oxidized unless another substance is reduced.
If one element gains electrons (reduction), it is because
another element lost them (oxidation).
An element will not lose electrons (oxidation) unless another
element takes them (reduction).
REMINDERS GIVEN IN LESSON:
OIL RIG
Oxidation Is Loss (of electrons)
Reduction Is Gain (of electrons)
LEO the lion says GER
Losing Electrons is Oxidation
Gaining Electrons is Reduction
Rules for Assigning Oxidation Numbers
· Neutral Elements
· Oxygen
· Monatomic Ions
· Covalent Compounds
· Algebraic Sum
Neutral Elements
Neutral elements in their standard state (not in a compound)
always have an oxidation number of zero.
Examples (all have an oxidation number of zero):
· O2
· Na
· F2
· S8
· P4
Oxygen
Oxygen always has an oxidation number of -2 when combined with
another element, except in peroxides, when it is -1.
Examples:
•H2O (O = -2)
•CaO (O = -2)
•H2O2 (O = -1 because peroxide)
Monatomic Ions
Monatomic ions have an oxidation number equal to their charge as
an ion (when alone or when in a compound).
Examples:
NaCl Na = +1, Cl = -1
· CaBr2 Ca = +2, Br = -1
· Ag+ Ag = +1
· Al3+ Al = +3
Covalent Compounds
For covalent compounds, pretend the compound is ionic with the
more electronegative element forming the negative ion (anion). For
example: Fluorine is always -1 in a compound, oxygen is almost
always -2, and hydrogen is +1 in covalent compounds.
Examples:
· CCl4 C = +4, Cl =
-1
· NH3 N = -3, H =
+1
Algebraic Sum
The algebraic sum of all the oxidation numbers (multiplied by
any subscripts) must add up to the total charge of the compound or
ion. This means we can use subtraction to solve for any elements
not listed in the previous oxidation number rules.
Covalent Compounds
For covalent compounds, pretend the compound is ionic with the
more electronegative element forming the negative ion (anion). For
example: Fluorine is always -1 in a compound, oxygen is almost
always -2, and hydrogen is +1 in covalent compounds.
Examples:
· CCl4 C = +4, Cl =
-1
· NH3 N = -3, H =
+1
Algebraic Sum
The algebraic sum of all the oxidation numbers (multiplied by
any subscripts) must add up to the total charge of the compound or
ion. This means we can use subtraction to solve for any elements
not listed in the previous oxidation number rules.
Oxidizing and Reducing Agents
In a redox reaction, one reactant is always an oxidizing agent
and another reactant is the reducing agent. It is easy to make a
mistake with these terms, so take time to define these terms in
your notebook, and to learn and practice these terms.
Agents
Oxidizing Agent: A reactant that causes another substance to be
oxidized (not being oxidized itself). The oxidizing agent is the
reactant that is reduced.
Reducing Agent: A reactant that causes another substance to be
reduced (not being reduced itself). The reducing agent is the
reactant that is oxidized.
This may seem backward because the oxidizing agent is being
reduced and the reducing agent is being oxidized, but remember that
if you are an agent of something, you cause that “something” to
happen to someone else. Define all of these terms in your notes and
review them because it can be easy to mix them up.
· An oxidizing agent causes another substance to be
oxidized.
· The only way to cause oxidation is to remove electrons from
that other substance (because oxidation is loss of electrons).
· Therefore, the oxidizing agent is reduced as it gains
electrons from the other substance.
Module 8!!!!!!!
Chemical vs. Nuclear Reactions
Atoms are made up of electrons, neutrons, and protons. In the
chemical reactions that we have studied throughout this course, the
sharing or exchange of electrons was involved in forming bonds and
compounds while the neutrons and protons remained unchanged in the
nuclei of the atoms.
However, some atoms have unstable nuclei because the number of
protons and neutrons are off balance. Atoms with unstable nuclei
are radioactive; they eventually break down into a different
substance and release energetic particles, or radiation, in the
process.
Alpha (α) Radiation
Alpha radiation is made up of a stream of alpha particles. Alpha
particles are made up of two protons and two neutrons released from
the nucleus of the radioactive atom. This means that alpha
particles have a positive charge, and that when an atom releases an
alpha particle, its atomic number decreases by two and its mass
number decreases by four.
Unstable parent nucleus → resulting daughter nucleus + alpha
particle
Alpha particles have a high amount of kinetic energy and can
cause damage to surface materials such as skin and living tissue.
However, alpha particles are relatively easy to shield against.
They cannot normally penetrate lightweight materials such as paper
or fabric. Also, as they travel through the air, the particles
attract electrons and become neutral helium atoms.
Beta (β) Radiation
Beta radiation is made up of a stream of beta particles. Beta
particles are fast-moving electrons released from a nucleus when a
neutron breaks apart into one proton and one electron.
Neutron → beta particle (electron) + proton
A negative beta particle, which is a very fast moving electron,
is released when a neutron decays. A positive proton is left behind
in the nucleus during this type of decay.
When the negative beta particle is released from the nucleus of
an atom, the atom ends up with one more proton and one less
neutron.
Beta particles have a negative charge and they usually move
faster than alpha particles. This means that beta particles are
more difficult to protect against than alpha particles; they can
penetrate cloth and paper. Beta particles can penetrate deeply into
skin and potentially harm or kill living cells. However, these
particles cannot penetrate thin layers of denser materials such as
aluminum and other metals. When beta particles are finally stopped
by a substance, they are absorbed by the material, like any other
electron.
Gamma (γ) Radiation
Gamma radiation can be given off during different types of
nuclear decay. Gamma rays are a form of electromagnetic waves with
a very high frequency and greater energy than ultraviolet light or
X-rays.
· Ultraviolet 10-6
· X-ray 10-8
· Gamma Ray 10-10 to 10-12
Because gamma rays have high energy and no mass or charge, they
can penetrate through most materials. Gamma rays can cause much
more damage to living cells than alpha or beta particles. Only very
dense materials, such as thick layers of lead, can stop gamma rays.
This is why lead is commonly used as a shielding material in
laboratories and hospitals where gamma radiation is present.
Overview
Alpha (α)
Beta (β)
Gamma (γ)
Made up of two protons and two neutrons bound together.
Made up of electrons.
High-frequency photons with no charge.
Move slowly and can be stopped by a sheet of paper or human
skin.
Move faster than alpha but lose their energy when they collide
with other atoms.
Can penetrate paper and aluminum, but are stopped by a thick
layer of lead or concrete (think of wearing lead vests when getting
x-rays).
Some beta particles can be stopped by human skin, but if they
are ingested, the particles can be absorbed into the bones and
cause damage.
If a person is exposed to gamma rays, severe damage to their
internal organs can occur.
Radioactive Decay
When a radioactive element’s nucleus decays and gives off an
alpha or beta particle, the number of protons and neutrons inside
the nucleus changes. When this happens, the atom becomes another
element. This is what makes nuclear reactions different than
regular chemical reactions. In a nuclear reaction, the identities
of the elements actually change, because protons and neutrons are
gained or lost by the atom over the course of the reaction.
REVIEW THE FOLLOWING CONCEPT OF HALF-LIFE EXTENSIVELY!!!!!! MAKE
SURE YOU REALLY KNOW HOW TO DO THIS!!!
Half-Life
Radioactive isotopes decay at different rates, but the rates are
all measured in terms of the substance’s half-life. Half-life is
the time needed for half of the radioactive atoms in a sample to
decay. The half-life of a given isotope is constant and is
independent of external conditions or the amount of atoms in the
sample. This means that the half-life of a specific isotope will be
the same whether you have one million moles or one mole of the
atoms.
Radium-226 has a half-life of 1,620 years, which means that half
of a given sample of radium-226 will decay into lead by the end of
1,620 years. In the next 1,620 years, half of the remaining sample
will decay into lead, leaving one-fourth of the original amount of
radium-226.
The half-lives of radioactive substances range from less than a
millionth of a second to more than a billion years. Uranium-238 has
a half-life of 4.5 billion years! So how can scientists measure
half-lives that are that long? The answer is that they do not
measure the actual half-life, but they can accurately measure the
rate of the isotope’s decay using a radiation detector. The faster
a substance decays, the more radiation per minute is detected, and
the shorter the half-life of a given isotope. It is not necessary
to wait through an entire half-life of a substance; the half-life
can be calculated using the rate of decay that is observed.
Once we know the half-life of a substance, this information can
be used to estimate the age of ancient remains. One of the most
common examples of this is the use of carbon-14 dating to estimate
the age of dead organisms or artifacts made of wood or cloth.
REVIEW 08.01 HALF-LIFE PRACTICE QUESTIONS
We know that the particles inside an atom’s nucleus are held
together by a strong nuclear force. If a large nucleus is split
apart, large amounts of energy can be released. In nuclear
fission
Fission: A nuclear reaction in which an atomic nucleus splits
into fragments, usually two fragments of comparable mass, with the
release of large amounts of energy in the form of heat and
radiation., certain heavy elements, such as some forms of uranium,
are split when they are struck by a moving neutron.
When an atom of uranium-235 is struck by a moving neutron, the
atom’s nucleus absorbs a neutron and becomes unstable. Instead of
giving off an alpha or beta particle, like in the other nuclear
reactions that we have studied, the heavy uranium isotope splits
into two or more smaller, medium-weight atoms.
As the nucleus splits, some free-moving neutrons are released
and can collide with more uranium-235 atoms to cause additional
fission reactions to occur. When the material or substance that
starts a reaction, in this case a neutron, is also produced by the
reaction and is available to start another reaction, the process is
called a chain reaction
Chain Reaction: A series of reactions in which the material or
substance that starts a reaction is also produced by the reaction
and is available to start another reaction.. This chain reaction
will continue to occur until all of the uranium-235 isotopes have
split, or until the neutrons fail to collide with any more
uranium-235 nuclei.
The fission of uranium-235 nuclei produces large amounts of
energy, estimated to be about seven million times that of the
explosion of a TNT molecule. This release of energy is what makes
nuclear fission useful as an energy source for communities, but it
also comes with possible risks and safety concerns. Most of the
energy released by nuclear fission is in the kinetic energy of the
fission fragments, the smaller atoms produced when the larger atoms
splits, and some of the energy is released as gamma radiation.
Nuclear Power Plants
The magnitude of the power of nuclear fission was introduced to
the world in the form of nuclear bombs, which can influence our
thinking about nuclear power. Although a similar chain reaction is
used in the nuclear fission that occurs in nuclear power plants,
the engineering and containment of the reaction is quite different
from that of a fission bomb.
According to the U.S. Energy Information Administration, nuclear
power plants contributed to 20.3 percent of the electrical power
supplied in the United States from June 2009 to May 2010.
Coal-fired power plants contributed 46.3 percent and natural
gas-fired plants contributed to 21.2 percent of the electrical
power in the United States over the same time period. Some
countries depend more on nuclear power than the United States. The
World Nuclear Association reports that France derives over 75
percent of its electricity from nuclear power, Armenia over 45
percent, and Belgium over 51 percent.
Nuclear power plants, like power plants that use fossil fuels,
boil water to produce steam that turns a large turbine. In a
nuclear power plant, a kilogram of uranium, about the size of a
baseball, produces more steam, and therefore more electricity, than
30 freight-car loads of coal.
Also, fission reactions do not produce the atmospheric
pollutants and greenhouse gases that are associated with the
combustion of fossil fuels. However, there are risks and
by-products associated with a nuclear fission that are different
than those associated with the use of fossil fuels. By
understanding more about nuclear reactions and power plants, we can
each make a more informed decision if someone proposes the
construction of a nuclear power plant in our community.
Nuclear Fusion
Nuclear fusion is very different than nuclear fission, but it
still involves large amounts of energy released as the nucleus of
an atom changes. In nuclear fusion
Fusion: A nuclear reaction in which the nuclei of two very small
atoms, such as two hydrogen isotopes, combine together into one
larger nucleus., the nuclei of two very small atoms, such as two
hydrogen isotopes, combine together into one larger nucleus. Do not
confuse this with a regular chemical reaction, where atoms combine
by sharing electrons. In nuclear fusion, it is the actual nuclei
that combine together to form one new atom, not the combination or
exchange of electrons to form a new compound.
The nuclear-fusion reaction below is one proposed by scientists
to someday be used in fusion reactors. In this reaction, two
different isotopes of hydrogen, deuterium and tritium, fuse
together to form one atom of helium, one neutron, and a very large
amount of energy.
REVIEW RENEWABLE AND NON RENEWABLE RESOURCES
These are really easy to remember as we have been learning them
since 3rd grade :) but it never hurts to refresh your memory!
REVIEW 08.04
It’s just about pollution and its effects on both humans and the
environment
Carbon Chemistry
Carbon atoms have the unique ability to bond with other carbon
atoms in long chains, rings, and other formations. This property
allows carbon to be the base of a variety of large molecules. Have
you ever heard the term “carbon-based life-form”? All humans are
carbon-based organisms, as are all animals and plants, because we
are made up of many different carbon compounds. Life is actually
based on carbon’s ability to form diverse molecular structures.
There is a branch of chemistry, called organic chemistry, dedicated
to the study of compounds that contain carbon.
Because organic compounds are the basis for living organisms and
are also used for a variety of applications, such as fuels,
medicines, agriculture, flavoring, and more, it is important to
have a basic understanding of them. In this lesson, we will discuss
the carbon atom and some categories of organic compounds that can
be formed because of the unique properties of carbon.
Carbon
Carbon is a nonmetal that is found in nature as both a pure
element and in various compounds. It is the 17th-most abundant
element, by mass, found on Earth, but it is one of the most
important elements to humans because it is found in all living
matter.
A carbon atom has four valence electrons in its outermost energy
level , and it has a strong tendency to share electrons to have a
full octet in its valence. Carbon atoms often naturally bond with
each other in chains, rings, plates, or networks, and they also
bond readily with hydrogen, oxygen, nitrogen, sulfur, phosphorus,
and the halogens.
Carbon occurs in two pure forms, diamond and graphite. These two
forms of carbon have very different properties due to the
difference in how the carbon atoms are covalently bonded
together.
Diamonds are the hardest material known to man. This solid form
of carbon is colorless with an extremely high density of 3.514
g/cm3. In a diamond, the carbon atoms are held together by all
single bonds formed in a three-dimensional tetrahedral formation.
This formation holds the carbon atoms together in a strong and
compact structure that makes diamonds so strong and dense.
Graphite is a soft, black, solid form of carbon that conducts
electricity reasonably well and is easily broken. The "lead" in
your pencil is actually graphite, so you can examine its properties
for yourself. The carbon atoms in graphite are arranged in layers
of thin hexagonal “plates.” This configuration of carbon atoms is
due to the fact that each carbon atom has one double bond and two
single bonds, forming a trigonal planar shape of bonds around each
carbon atom. The layers of carbon atoms in graphite are only held
together by the weak London dispersion intermolecular force, which
explains why graphite is so soft and easily broken.
Categories of Organic Compounds
Organic compounds all contain carbon atoms. There are only a few
carbon compounds, such as organic compounds like NaCO3 and the
oxides of carbon (CO and CO2), that are not considered organic.
Because of carbon’s ability to form different combinations of
single, double, and triple covalent bonds, the number of possible
carbon compounds is virtually unlimited. There are more than 4
million naturally occurring and man-made organic compounds
currently known.
Carbon can fill its valence energy level by sharing a total of
four pairs of electrons. This means that a given carbon atom can
form four single bonds, two single bonds and one double bond, two
double bonds, or one triple bond and one single bond.
REVIEW SLIDES AT THE BOTTOM OF LESSON 08.05
Biochemistry
Biochemistry, as its name suggests, is a field of science that
combines biology and chemistry. Specifically, it is the study of
the chemistry involved with living organisms. This means that
biochemists study the atoms, molecules, and chemical reactions that
are found in, or affect, living organisms.
Biochemistry is much more than the study of the molecules found
in living systems. It is a study of the reactions that produce or
use these substances, and it helps answer questions about how
organisms live, move, function, and respond to stimuli.
Every living cell is a biochemical factory, building and
dismantling molecules in a variety of chemical reactions. The
energy needed to fuel these reactions is provided by the food that
the organisms eat. All of the biochemical reactions that occur in a
given organism are collectively called its metabolism
Metabolism: All of the biochemical reactions that occur within a
given organism, and the reactions are organized into metabolic
pathways to be studied and tested.
Ex: I don’t gain weight easily because I have a really fast
metabolism
Biotechnology
Biotechnology is the application of the knowledge of
biochemistry to create new products or processes that are useful to
humans. Advances in biotechnology have affected our lives in many
ways. A few examples of biotechnology include:
Biotechnology touches our lives in many ways. Listed below are
some highlights.
Agriculture: Biotechnology allows scientists to transfer genes
from one plant species to another. For example, a scientist might
transfer a gene that gives one kind of plant a resistance to salt
into a crop plant. The crop plant may then be able to grow under
higher salt conditions.
Forensics: Forensic scientists can get DNA from blood, skin
cells, and other bodily substances. They can compare the DNA in
samples found at a crime scene with DNA from possible victims and
suspects. By comparing DNA sequences, they can link suspects and
victims to crime scenes
Genetic Research: Many diseases are caused by specific genes.
Scientists can screen people for some of these genes. This
information can help people make important decisions about their
health.
Drug Research: Scientists are developing devices that use
computers and living cells to study the effects of different drugs.
These devices allow scientists to greatly reduce the number of
animals used in drug research.
Vaccines and Medicine: Biotechnology can help scientists produce
vaccines and other drugs. Scientists can genetically modify
bacteria so that they produce the vaccine or drug in very large
quantities.
GOOD
LUCK!!