Unit 2: Essentials of Chemistry Chapter 1-2, 4-5
Objectives 8 explain the nature of science including the use of the validity of the scientific method and the
difference between a hypothesis, theory and law
9 explain the three major states of matter and their physical and chemical characteristics
10 explain and give examples of physical properties and chemical properties
11 explain and give examples of physical changes and chemical changes
12 identify the five pieces of evidence that a chemical reaction has occurred
13 define and classify matter including pure substances mixtures.
14 understand the historical progression of structure of the atom including such models created by Democritus, Dalton, Thomson, Rutherford, Bohr, and Schrodinger
15 define and identify examples of the laws of conservation of mass, definite proportions, and multiple proportions
16 identify the structure of an atom including the relative masses of a proton, neutron, and electron, their relative charges, and locations in the atom
17 define and identify isotopes and ions
18 define and distinguish between atomic number and mass number and identify the parts of the nuclear symbol
19 define and calculate average atomic mass in amu’s
20 understand and record the arrangement of electrons in an atom including Hund’s rule, the Pauli exclusion principle, and the Aufbau principle by writing the orbital notation and electon configuration for specific elements
8 Explain the Nature of Science
The nature of science refers to how science is actually performed.
It explains the scientific view point on solving problems and why certain ideas are not considered.
There are several nature of science ideas which will be discussed on the next few slides
Nature of Science Ideas
1. While science strives to be objective, it cannot be entirely.
◦ It is human nature to use previous experiences and knowledge. This allows scientists to make logical conclusions even though it is not completely objective.
◦ For example: Imagine you were trying to determine an object in a shoebox. An objective scientist would have to try everything. This would be tedious and waste time because certain objects would not fit (like an elephant). By using prior knowledge, certain objects can be eliminated and the object can be identified faster.
Nature of Science Ideas
2. Science needs experimental evidence.
◦ In order for something to be considered
scientifically supported, it must be able to be
tested.
◦ Only testable evidence will be accepted by the
scientific community. They will not accept
unless some experiment supports it. Great
scientists have proposed ideas well ahead of
their time, but these ideas were not accepted
because there was no evidence to support
their claims.
Nature of Science Ideas
3. Science neither accepts or denies the existence of the supernatural.
◦ Supernatural beings are considered to be outside the realm of science.
◦ A supernatural being can change the natural world at their will so science cannot test for their existence.
◦ Because science cannot test it, science cannot make a statement one way or the other on the existence of the supernatural.
◦ Science only tries to develop conclusions based on ideas that can be tested.
Nature of Science Ideas
4. Science cannot prove anything 100% which makes it a flexible subject. ◦ As that science relies on data and evidence, it can
only support ideas.
◦ As new evidence is generated, this support can strengthen or weaken.
◦ Often new technology allows for new information to be discovered.
◦ For example: In ancient Greece, it was believed atoms were the smallest particles. However, in the early 1900s, scientists used new technology to show that atoms were made of sub-atomic particles (protons and electrons). The idea that atoms were the smallest particles was no longer supported with this new data.
The Scientific Method
When looking at how science is performed,
the scientific method must be discussed.
It is designed with a few steps which are:
◦ Observe a situation
◦ Make a hypothesis
◦ Test the hypothesis
◦ Make a conclusion
Other sources may provide more steps to
the method but it can be condensed to
these four.
The Scientific Method
The scientific method is an excellent
problem solving guide because it is flexible.
It allows for the scientists to start at any
point and proceed with solving the problem
◦ For example, imagine you are performing an
experiment and observe a change unrelated to
your experiment. This could be the beginning of
a new hypothesis yet it did not come from simply
observing the natural world.
This method for solving problems works for
all problems and not just scientific ones.
Hypothesis, Theory, and Law
These three terms are often confused when discussing the nature of science.
A hypothesis is an educated analysis of an observation. It requires testing and is essential an explanation of a phenomena.
A theory is a hypothesis with enough evidence to be accepted as fact. It explains the how and why qualitatively.
A law is a hypothesis with enough evidence to be accepted as fact. It describes the what quantitatively.
Hypothesis, Theory, and Law
Hypothesis
Theory Law
It is possible to change a theory or a law if
there is evidence to support such a change.
Can become with enough
experimental evidence
Can become with enough
experimental evidence
Both are accepted as fact and
cannot become the other
9 States of Matter
There are actually five known states of
matter. Three are common and will be
discussed in greater detail.
◦ Solid
◦ Liquid
◦ Gas
◦ Plasma (occurs in the sun)
◦ Bose-Einstein Condensate (occurs when
temperatures approach -273°C)
Solids
Solids have a defined shape and a defined
volume.
The atoms that make up its structure are
very close together and are limited in their
movement.
Liquids
Liquids have a undefined shape but a defined
volume.
The atoms that make up its structure are
free to move around within its volume.
Gases
Gases have an undefined shape and an
undefined volume.
Their atoms are free to move about the
entire volume presented.
10. Properties
Each substance has a set of properties
(descriptions). These can fall into two
categories:
Physical and Chemical
Physical properties describe
or measure the object
without changing it.
Chemical properties describe
the substance’s ability to
undergo a change.
Example: color, smell, mass Example: ability to rust, flamability
11. Changes
Each substance also can undergo a change
and the same two categories apply:
Physical and Chemical
Physical change is a change
in which the substance is
altered but can be returned
to its original state.
Chemical change is a change in
which the substance is altered
at the molecular level and
cannot be returned to its
original state.
Example: smashing, tearing Example: baking, burning
Phase changes
Phase changes occur when one state of matter becomes another.
◦ Melting S L
◦ Freezing L S
◦ Vaporization L G
◦ Condensation G L
◦ Sublimation S G
◦ Deposition G S
Since these changes can be reversed to get the original back, phase changes are a type of physical change.
12. Evidence for a chemical change
Chemical changes can be more challenging
to determine.
To help in this matter, there a some pieces
of evidence to look for in the event of a
chemical change.
◦ Color change
◦ Formation of a Precipitant
◦ Emission of heat
◦ Emission of light
◦ Emission of a gas
The videos these are linked
to are from youtube.com as
of July 26, 2011
13. Classifying Matter
As discussed earlier, there are three main
types of matter: solid, liquid, and gas.
Matter can be broken down into two
categories: Pure substances and Mixtures
◦ A pure substance consists of only one
component and it has unique chemical and
physical properties.
◦ A mixture is a combination of two or more pure
substances.
Pure Substances
Pure substances can be broken down into a
few different terms. All of the following have
unique chemical and physical properties.
Term Description
Atom The smallest particle with unique
characteristics.
Element Multiple atoms of the same type
Compound Two or more different atoms bonded
together
Molecule Two or more atoms (can be the same
atom) bonded together
Allotropes
An allotrope is an unique type of molecule.
Allotropes are atoms of the same type that
bond to themselves in multiple ways.
◦ For example: Oxygen
Oxygen gas is O2 which means there are two oxygen
atoms
Ozone gas is O3 which means there are three oxygen
atoms.
Mixtures
Mixtures are two or more pure substances
and can be mixed differently.
◦ Homogenous mixtures are thoroughly mixed and
the parts are uniform throughout.
Any solution is a good example.
◦ Heterogeneous mixtures are not uniform and
the parts can be seen mixed throughout.
Most mixtures are heterogeneous and a good example
of this would be a chocolate chip cookie.
14. History of the atom • ~400 BC Introduced the indestructible atom Democritus
• Late 1700s Law of Conservation of Mass Antoine Lavoisier
• Early 1800s Atomic Theory John Dalton
• 1897 Discovered the electron JJ Thomson
• 1898 Discovered radioactivity Marie Curie
• 1909 Gold-Foil Experiment Ernest Rutherford
• 1913 Determined the charge of an electron Robert Millikan
• 1913 Discovered energy levels for electrons Niels Bohr
• 1926 Discovered atomic orbitals Erwin Schrodinger
• 1932 Discovered the neutron James Chadwick
• 1935 Discovered artificial radioactivity Irene Jolliet-Curie
Dalton’s Atomic Theory
1. Elements are made of tiny particles called atoms.
2. Atoms of an element are different from other elements and can be distinguished by their atomic masses.
3. All atoms of a given element must be identical in properties.
4. Atoms of an element can combine with atoms of a different element to for compounds.
5. Chemical reactions rearrange the atoms but cannot create or destroy atoms. Return
Thomson’s Plum Pudding Model
As that Thomson discovered the
electron, that meant the atom
contained smaller parts.
This would change the model used
for the atom.
◦ The model used to be a solid sphere
◦ The plum pudding model used
electrons as the “plums” and the rest
of the atom as the “pudding”.
◦ The plums were negative and the
pudding was positive.
Return
Gold Foil Experiment
The gold foil experiment was conducted by Ernest Rutherford and his graduate students, Hans Geiger and Robert Marsden.
By shooting alpha particles at a gold foil, they noticed the particles essentially went straight through.
This led them to conclude the atom was mostly empty space with a dense positive core (protons.
Return
Picture was taken from: http://www.kentchemistry.com/links/AtomicStructure/rutherfordtutorial.htm on
July 28, 2011.
Bohr Model of the Atom
Niels Bohr created an atomic model after
doing work with the color spectra
emitted from a hydrogen atom.
His model is sometimes called the solar
system model.
The following link provides a more
detailed description (the first 15 slides
covers Bohr):
http://science.sbcc.edu/physics/solar/science
segment/bohratom.swf Return
Schrodinger’s Orbitals
The current model of the atom uses the orbitals discovered by Schrodinger.
Within each energy level, there exists four kinds of orbitals: s, p, d, and f.
Each can hold a certain number of electrons.
The shape of each orbital is shown on the next slide.
◦ The image was taken from: http://chemwiki.ucdavis.edu/Physical_Chemistry/Quantum_Mechanics/Atomic_Theory/Electrons_in_Atoms/Electronic_Orbitals on July 28th, 2011.
Return
15. Define and Identify Three Laws
Law of Conservation of Mass
◦ The law of conservation of mass states that mass
can be mass can neither be created or destroyed.
◦ This means that the products of a chemical
reaction will have the same mass as the
reactants.
15. Define and Identify Three Laws
Law of Definite Proportions
◦ This law states that any sample of a compound
has the same composition.
◦ This means that water will always be H2O
whether it is found in Iowa or somewhere else.
15. Define and Identify Three Laws
Law of Multiple Proportions
◦ This law states that the mass ratio for one of the
elements in a compound that combines with a
fixed mass of another element can be expressed
in small whole numbers.
Compound % Oxygen % Nitrogen %O ÷ %N Mass Ratio
NO2 69.56 30.44 2.285 4
NO 53.32 46.68 1.142 2
N 2O 36.35 63.65 0.571 1
16. Identify the structure of the
atom The atom is constructed of three basic
subatomic particles.
◦ In the last 20 years, it has been discovered that
quarks make up both protons and neutrons.
Subatomic
Particle
Location Charge Approximate
Mass
Proton Nucleus +1 1 amu
Electron Electron Cloud -1 0.00055 amu
Neutron Nucleus 0 1 amu
Structure of the Atom-Bohr Model
This picture came from http://www.universetoday.com/82128/parts-of-an-atom/ on
August 31, 2011.
17. Isotopes and Ions
Each atom can have different variations.
All atoms are identified by the number of
protons they contain.
◦ Oxygen will always have 8 protons. If you added
an additional proton, the atom would no longer
be oxygen (it would be fluorine).
The number of neutrons and electrons can
vary slightly.
Isotopes-changes in neutrons
Protons contain a positive charge. When an atom becomes large, it contains several protons. That much positive charge in one location is unstable.
Neutrons, which have no charge, act as spacers in between the protons.
An isotope is the name of an atom with different amounts of neutrons.
◦ Oxygen for example has three common isotopes.
Oxygen-16 has 8 neutrons
Oxygen-17 has 9 neutrons
Oxygen-18 has 10 neutrons
Ions-changes in electrons
Electrons fill the orbitals surrounding the
nucleus.
This is known as the electron cloud.
In a neutral atom, each proton has an
electron in the electron cloud.
When an atom becomes charged, the
number of electrons no longer matches the
protons.
◦ Positive charges indicate a loss of an electron.
◦ Negative charges indicate a gain of an electron.
18. Nuclear Symbols
Nuclear symbols are useful for determining
the amount of electrons, protons, and
neutrons in an element.
Mass number: Shows
the number of neutrons
and the number of
protons.
Atomic Number: Shows
the number of protons.
Charge: Indicates the
difference between the
electrons and protons.
Negative charges indicate
more electrons while
positive charges indicate
more protons.
19. Average atomic mass
On the Periodic Table, the mass listed is the
average atomic mass.
This is an average of all the naturally
occurring isotopes of an atom.
Calculating an average for a large amount of
particles can be challenging.
Average Atomic Mass
Carbon has three common isotopes.
◦ Carbon-12
◦ Carbon-13
◦ Carbon-14
These three common isotopes do not come
in equal amounts though:
◦ 98.89% is carbon-12
◦ 1.10% is carbon-13
◦ 0.01% is carbon-14
Average atomic mass
To determine the average atomic mass, the
following formula should be used:
(Atomic Mass x Percent Abundance) + (Atomic Mass x Percent Abundance)
+…..=average atomic mass
So in the case of carbon: (12.00 amu x .9889) + (13.00 amu x 0.0111) + (14.00 amu x 0.0001) =
12.01 amu
20. Arrangement of Electrons
According to Bohr and Schrodinger,
electrons surround the atom in energy levels
that take the form of orbitals.
The Periodic Table is broken into four
sections that correlate to the orbitals
The placement of electrons within these
orbitals follow set rules.
Arrangement of Electrons
Hund’s Rule
◦ Electrons will fill the available orbitals at a certain
energy level before pairing.
Pauli Exclusion Principle
◦ Only two electrons can occupy each orbital and
their spins will be opposite.
Aufbau Principle
◦ The lowest-energy orbitals will be filled first.
Below is a depiction of how the Periodic
Table shows the orbitals (SPDF).
S
F
D
P
Energies of Each Level
The orbitals correspond to different levels
of energies.
In general, each row on the Periodic Table
represents a different level of energy.
It gets more complicated farther down the
Periodic Table.
Energies of Each Level 7p ___ ___ ___
6d ___ ___ ___ ___ ___
5f ___ ___ ___ ___ ___ ___ ___
7s ___
6p ___ ___ ___
5d ___ ___ ___ ___ ___
4f ___ ___ ___ ___ ___ ___ ___
6s ___
5p ___ ___ ___
4d ___ ___ ___ ___ ___
5s ___
4p ___
3d ___ ___ ___ ___ ___
4s ___
3p ___ ___ ___
3s ___
2p ___ ___ ___
2s ___
1s ___
As you progress from the 1s to
the 7p, you increase the amount
of energy. Notice how the d-
sublevel is always after the s-
sublevel of the previous energy
level (example 3d follows 4s).
Notice the f-sublevel follows
the s-sublevel of two energy
levels before it (example: 4f
follows 6s).
Energ
y
2.14 Orbital Notation
To show orbital notation, the three rules
must be followed.
◦ Therefore, start at the lowest energy level.
◦ Designate an electron by drawing an arrow
The arrow indicates the spin
◦ Place one electron in each orbital until they each
have one on that level. Then go back and pair
them.
◦ Only two electrons fit in each orbital.
◦ The arrows must point in opposite directions to
show opposite spins.
Orbital Notation
Look at the element sulfur-32.
First determine the number of electrons
◦ Since sulfur has an atomic number of 16, it has
16 protons, 16 electrons, and 16 neutrons.
3p ___ ___ ___
3s ___
2p ___ ___ ___
2s ___
1s ___
Place electrons in the first energy level and
continue up.
When 2p is hit, fill each orbital and then go
back and pair.
Finish by repeating the process used for 2p
but stop when you hit 16 arrows.
This is the orbital notation.
Electron Configuration
Orbital notation can take up a lot of space.
It does a nice job of giving a visual of the
location of each electron.
Electron configuration is a shorthand
notation for determining the location of the
electrons.
It follows the same rules but is slightly easier
to write.
Electron Configuration
As you read across the Periodic Table, you can pick out the
electron configuration.
The electron configuration for oxygen-16 is:
O:1s2 2s2 2p4
Red represents the s-sublevel and yellow is the p-sublevel.
Each row is an energy level.
Since oxygen has eight electrons, we count eight boxes.
The superscripts on the sublevels indicate the number of
electrons.
Electron Configuration
The same rules apply to the d and f
sublevels.
Example: Gold-196 (79 electrons)
Au: 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d9
This concludes the tutorial on
measurements.
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Definitions-Select the word to return to the tutorial
Qualitatively
◦ Refers to a description or observations
Quantitatively
◦ Refers to a measured amount; uses numbers
Objective
◦ Not influenced by personal feelings or
interpretations.