Chapter 2 The Chemistry of Life. The atom is the basic unit of all matter. It is the smallest piece…

Chapter 2 The Chemistry of Life

• The atom is the basic unit of all matter. It is the smallest piece of a substance that can still be a particular substance. Break it down any more and you have something different.

• The subatomic particles that make up an atom are protons, neutrons, and electrons.

• Protons and neutrons have about the same mass.

• Protons have a positive + charge.• Neutrons have no charge. They are neutral.• Protons and neutrons make up the nucleus of

the atom. (the center)

• The electron is negatively charged.• It is very small compared to the proton and

neutron. (1840 times smaller)• Electrons are in constant motion around the

nucleus of the atom.• Normal atoms have equal amount of electrons

and protons, so the positive and negative charges cancel out; the atom is neutral.

• A chemical element is a pure substance that consists entirely of one kind of atom.

• Elements have a one or two letter symbol.• Atomic number is the number of protons in

the elements nucleus.

6

CCarbon12.011

Section 2-1

An Element in the Periodic Table

• Isotopes-atoms of the same element that have different numbers of neutrons.

• Mass number-the sum of the protons and the neutrons in the nucleus.

• Carbon-12, Carbon-13, and Carbon-14 are examples of Carbon isotopes.

• The weighted average of the masses of the element’s isotopes is called its atomic mass.

• Weighted means that the abundance of each isotope in nature is considered when the average is calculated.

• Some isotopes are radioactive.• This means that their nuclei are unstable and

break down at a constant rate over time.

Nonradioactive carbon-12 Nonradioactive carbon-13 Radioactive carbon-14

6 electrons6 protons6 neutrons

6 electrons6 protons8 neutrons

6 electrons6 protons7 neutrons

Section 2-1

Figure 2-2 Isotopes of Carbon

• Chemical Compounds-a substance formed by the chemical combination of two or more elements in definite proportions.

• Water H2O 2 atoms of H for every O• Table Salt NaCl 1 atom of Na for every Cl

• Chemical Bonds-hold atoms together in compounds.

• Bond formation involves the electrons that surround the nucleus.

• The electrons that are available to form bonds are called valence electrons.

• The 2 main types of bonds are called ionic and covalent bonds.

• Ionic Bonds-are formed when one or more electrons is transferred (stolen) from one atom to another.

• When a neutral atom loses an electron it becomes more positive.

• When a neutral atom gains an electron it becomes more negative.

• These positive and negative atoms are ions.

• Oppositely charged atoms are strongly attracted to each other. This is the basis for an ionic bond.

• Covalent Bonds-occur when electrons are shared by two or more atoms instead of being transferred or stolen.

• The structure that results when atoms are joined together by a covalent bond is called a molecule.

• A molecule is the smallest unit of most compounds.

Sodium atom (Na) Chlorine atom (Cl) Sodium ion (Na+) Chloride ion (Cl-)

Transferof electron

Protons +11Electrons -11Charge 0

Protons +17Electrons -17Charge 0

Protons +11Electrons -10Charge +1

Protons +17Electrons -18Charge -1

Section 2-1

Figure 2-3 Ionic Bonding

Section 2-2 Properties of Water

• Water is POLAR• Oxygen has 8 protons while hydrogen atoms

only have 1 proton. This causes the oxygen atoms to have a greater attraction for the electrons in the water molecule.

• This creates the probability that you will find the shared electrons in a water molecule to be closer to the oxygen atom.

• Since a water molecule has a bent shape, the oxygen end will have a slight negative charge while the hydrogen end will have a slight positive charge.

• This causes a water molecule to act like a magnet with poles.

Hydrogen Bonds

• Because water is polar, it can attract other water molecules.

• Weak bonds called hydrogen bonds hold water molecules together. Water molecules can be involved in as many as 4 hydrogen bonds at one time.

• COHESION is an attraction between molecules of the same substance. Hydrogen bonding makes water extremely cohesive.

• This is why water beads up on smooth surfaces and some insects and spiders can walk on water.

• ADHESION is an attraction between molecules of different substances. (Graduated cylinder)

• A MIXTURE is a material made of two or more elements or compounds that are physically mixed together but not chemically combined.

• Examples: salt and pepper, sand and sugar.• 2 types of mixtures are Solutions and

Suspensions.

• Solutions consists of a SOLUTE, that substance that is dissolved, and a SOLVENT, the substance that does the dissolving.

• Water’s polarity gives it the ability to dissolve ionic and polar compounds. It is known as the universal solvent.

• Suspensions contain material that does not dissolve when placed in water. Instead, these particles separate into very small pieces.

• The pH Scale: A scale derived to measure the amount of H+ ions in a solution.

• The pH scale ranges from 0-14. 7 is neutral, and the amount of H+ and OH- ions is equal.

• pH numbers between 0-7 are acids.• The lower the pH, the stronger the acid. • pH numbers between 7-14 are bases.• The higher the pH, the stronger the base.• An acid is a compound that forms H+ ions in

solution.• A base is a compound that for OH- ions in

solution.

• Buffers are weak acids or bases that react with strong acids or bases to prevent sudden, sharp changes in pH.

• This is one way your body maintains homeostasis. Most fluids in your body cells must stay in a pH range between 6.5 and 7.5

Oven cleaner

Bleach

Ammonia solution

Soap

Sea water

Human bloodPure waterMilkNormalrainfall

Acid rainTomatojuice

Lemon juice

Stomach acid

NeutralIn

crea

sing

ly B

asic

Incr

easi

ngly

Aci

dic

Section 2-2

pH Scale

Section 2-2

Figure 2-9 NaCI Solution

Cl-

Water

Cl-

Na+

Water

Na+

2-3 Carbon Compounds

• Carbon is so important and interesting that a whole branch of Chemistry is devoted to it:

• Organic Chemistry• Why? Because carbon has 4 valence electrons

which can join with an electron from another atom forming a strong covalent bond.

• Even more important, carbon can bond to other carbon atoms, which gives carbon the ability to form long chains that are almost unlimited in length.

• These carbon-carbon bonds can be single, double, or even triple bonds.

Methane Acetylene Butadiene Benzene Isooctane

Section 2-3

Figure 2-11 Carbon Compounds

Macromolecules

• The word macromolecule means “giant molecule.”

• Macromolecules are made from thousands or even hundreds of thousands of smaller molecules.

• You call the process of making macromolecules polymerization.

• Polymerization is accomplished by joining small compounds together to make really large ones.

• The small compounds are called monomers.• Monomers are joined together to form

polymers.

• There are 4 groups of carbon compounds found in living things:

• 1. Carbohydrates• 2. Lipids• 3. Nucleic Acids• 4. Proteins

CarbonCompounds

include

that consist of

which contain

that consist of that consist of that consist of

which contain which contain which contain

Section 2-3

Concept Map

Carbohydrates Lipids Nucleic acids Proteins

Sugars and starches Fats and oils Nucleotides Amino Acids

Carbon,hydrogen,

oxygen

Carbon,hydrogen,

oxygen

Carbon,hydrogen,oxygen, nitrogen,

phosphorus

Carbon,hydrogen,oxygen,

nitrogen,

Carbohydrates

• Carbohydrates are made up of carbon, hydrogen, and oxygen atoms, usually in ratios of 1:2:1

• Carbohydrates are the main energy source for living things.

• Plants and some animals also carbs for structural purposes.

• Simple sugars provide immediate energy for cell activities.

• Extra sugars are stored as complex structures called starches.

• A single sugar is called a monosaccharide (glucose, galactose, and fructose)

• When you put monosaccharides together to form larger sugars you have created a polysaccharide. (glycogen and cellulose)

Starch

Glucose

Section 2-3

Figure 2-13 A Starch

Lipids

• Lipids are generally not soluble in water.• Lipids are made mostly from carbon and

hydrogen atoms.• Common lipids are fats, oils, and waxes.• Lipids can be used to store energy, and some

lipids play a part in cell membranes and waterproof coverings.

• Lipids are formed when a glycerol combines with a fatty acid.

• If each C atom is joined to another C atom by a single bond, it is called saturated.

• If a (C=C) double bond exists, it is called unsaturated.

• More than one (C=C=C) double bond is said to be polyunsaturated.

Nucleic Acids

• Nucleic acids are macromolecules containing hydrogen, oxygen, nitrogen, carbon, and phosphorus.

• The monomers that make up nucleic acids are called Nucleotides.

• Nucleotides have 3 parts:

• 1. a 5-carbon sugar• 2. a phosphate group• 3. a nitrogenous base• Individual nucleotides are joined together by

covalent bonds to form nucleic acids.• Their purpose is to store and transmit

hereditary (genetic) information.

• There are 2 kinds of nucleic acids:• 1. Ribonucleic Acid (RNA)• 2. Deoxyribonucleic Acid (DNA)• The difference in these 2 are their 5-carbon

sugars:• Ribose and Deoxyribose

Proteins

• Proteins are macromolecules that contain nitrogen, carbon, hydrogen, and oxygen.

• The monomers that make up proteins are called amino acids.

• There are 20 amino acids your body uses to make proteins. Only about half can be made by your body, the others must be consumed in your diet.

2-4 Chemical Reactions/Enzymes

• A chemical reaction is a process that changes, or transforms one set of chemical into another.

• Mass and energy are conserved during chemical reactions, which means that you end up with the same amount of mass and energy that you start with when the reaction is over.

• The elements or compounds that enter into a reaction are called the reactants.

• The elements or compounds produced by a chemical reaction are called the products.

Energy in Reactions

• Some chemical reactions release energy. These reactions often happen spontaneously.

• Exothermic• Other reactions absorb energy in order to

start. These will not occur without a source of heat or energy.

• Endothermic

Activation Energy

• Chemists call the energy needed to start a reaction Activation Energy.

Energy-Absorbing Reaction Energy-Releasing Reaction

Products

Products

Activation energy

Activation energy

Reactants

Reactants

Section 2-4

Figure 2-19 Chemical Reactions

Enzymes

• A catalyst is a substance that speeds up the rate of a reaction.

• Catalysts work by lowering a reaction’s activation energy.

• Enzymes are proteins that act as biological catalysts.

• Enzymes speed up the chemical reactions that take place within the cell.

Reaction pathwaywithout enzyme Activation energy

without enzyme

Activationenergywith enzymeReaction pathway

with enzyme

Reactants

Products

Section 2-4

Effect of Enzymes