1. Chapter 2 Chemistry of Life
Dr. R.M. Moody

2. Matter
Matter is anything that occupies space and has mass (e.g., solids, liquids and gases).
Atoms are the building blocks of all matter.
Elements are pure substances that contain only one type of atom.
An atom is the smallest unit of matter that retains the properties of a particular element.
Dr. R.M. Moody

3. States of Matter

4. Structure of Atoms
Atoms consist of a nucleus (“core”), which is orbited by electrons.
Subatomic particles of the nucleus:
Protons – Positively charged particles
Neutrons – Particles with a neutral charge
Electrons have a negative charge
Electrons move around the nucleus in an orbital.
Number of electrons is equal to the number of protons.
Only the outermost electrons take part in chemical reactions.
Dr. R.M. Moody

5. Atoms are mostly empty space
Atoms are mostly empty space. If you scaled a hydrogen atom to the size of a football stadium, the nucleus would be the size of a pea!
Dr. R.M. Moody

6. Structure of Atoms
All atoms of a given element have the same number of protons in the nucleus. This is called the atomic number.
The atomic number determines the identity and chemical properties of an element.
The mass number is the number of protons plus the number of neutrons.
Helium Atom
Atomic number: 2
Protons: 2
Neutrons: 2
Electrons: 2
Mass number: 4
Dr. R.M. Moody

7. He was even able to predict the existence of undiscovered elements!
In 1869, Dmitry Mendeleyev arranged elements known at the time by their chemical properties.
He was even able to predict the existence of undiscovered elements!
Dr. R.M. Moody

8. Chemical Composition of Organisms
Four elements make up ~96% of all organisms:
Oxygen: 65%
Carbon: 18.5%
Hydrogen: 9.5%
Nitrogen: 3.3%
Other important elements include: calcium, phosphorous, potassium, and sulfur.
Dr. R.M. Moody

9. Isotopes
Atoms that have the same number of protons but different numbers of neutrons are called isotopes.
Isotopes are defined by their mass number (protons + neutrons).
Example: Carbon isotopes
Dr. R.M. Moody

10. Notice that the number of protons remain the same—they are what make carbon, carbon!
Dr. R.M. Moody

11. From Atoms to Molecules
A chemical bond is an attractive force between atoms. They form when atoms:
Give away or gain electrons (ionic bonds)
Share electrons (covalent bonds)
A molecule is formed when two or more (same or different) atoms bond together.
Compounds are molecules containing atoms of two or more elements in fixed proportions.
All compounds are molecules, but not all molecules are compounds.
Dr. R.M. Moody

12. Ionic Bonds
Ionic bonds: A chemical bond that forms between an atom that gains an electron and an atom that loses an electron.
An atom with a charge is called an ion.
Ions with opposite charges (+ or -) attract one another, forming an ionic bond.
Dr. R.M. Moody

13. Sodium Chloride (table salt)
Note that the number of protons does not change!!

14. Covalent Bonds
Covalent bonds: Atoms share one or more pairs of electrons.
Strongest type of chemical bond
Dr. R.M. Moody

15. Polar and Nonpolar Covalent Bonds
In a nonpolar covalent bond, atoms share electrons equally. Atomic charges are equally distributed.
In a polar covalent bonds, atoms share electrons unequally. Partial positive and negative charges form on each end of molecule.
Dr. R.M. Moody

16. Two hydrogen atoms share two electrons in a single, nonpolar covalent bond.
(H-H)

17. molecular oxygen (O2) O=O
Two oxygen atoms share four electrons in a double, nonpolar covalent bond.
molecular oxygen (O2)
O=O

18. (δ+) (δ-) Water (H2O) H-O-H
In water, two hydrogen atoms share electrons with an oxygen atom in two polar covalent bonds.
The oxygen exerts a greater pull on the shared electrons, so it has a slight negative charge. Each hydrogen has a slight positive charge.
(δ+)
(δ-)
Water (H2O)
H-O-H

19. Chemical Bookkeeping Use symbols for elements when writing formulas
Formula for glucose is C6H12O6
6 carbons
12 hydrogens
6 oxygens
Dr. R.M. Moody

20. Chemical Reactions
Chemical Reaction: Process by which the atoms of one or more substance are rearranged to form different substances.
Example:
LIGHT ENERGY
12H2O + 6CO O2 + C6 H12O6 + 6H2O
REACTANTS
PRODUCTS
Dr. R.M. Moody

21. Activation Energy
Most reactions require energy to begin. This energy is called activation energy.
Chemicals that help speed up reactions are called catalysts.
Enzymes are used as catalysts in organisms:
Proteins
RNA
Dr. R.M. Moody

23. Oxidation-Reduction Reactions
Many reactions that transfer energy in living things involve the transfer of electrons.
Redox reactions involve the loss or gain of electrons:
Reduction: Gain electrons  Becomes (-)
Oxidation: Lose electrons  Becomes (+)
Remember: OIL RIG
Dr. R.M. Moody

24. Emergent Properties of Water
(water drop activity)
Dr. R.M. Moody

25. Hydrogen Bonding Recall that water is a polar molecule.
Hydrogen has a partial (+) charge
Oxygen has a partial (-) charge
A hydrogen bond is the force of attraction between a partially charged hydrogen and an atom or molecule with a partial or full negative charge.
Dr. R.M. Moody

26. Hydrogen Bonding
H-bonds impart structure to liquid water and stabilize nucleic acids and other large molecules.
(δ+)
(δ-)

27. Emergent Properties of Water
(1) Water is a great solvent because ions and polar molecules dissolve in it.
Polar substances are hydrophilic (“water- loving”); nonpolar ones are hydrophobic (“water-fearing”) and are repelled by water (e.g., oil has nonpolar bonds).
Solutes dissolved in a solvent form a solution.
Concentration refers to the amount of solute in a solution.
Dr. R.M. Moody

28. Emergent Properties of Water
(2) Water tends to stabilize temperature because it can absorb considerable heat before its temperature changes.
(3) Hydrogen bonding of water molecules provides cohesion and adhesion.
Dr. R.M. Moody

29. Emergent Properties of Water
(4) Water expands when it freezes (10% less dense).
If water didn’t float, much of life wouldn’t exist--ice would sink to the bottom of bodies or water and would not provide insulation.
Figure 2.11
Antarctic bottom water; gaseous water
Dr. R.M. Moody

30. Acids and Bases
Water molecules spontaneously separate into hydrogen ions (H+) and hydroxide ions (OH-) ions.
Hydrogen ions can then bond with water to form hydronium ions (H3O+).
H3O+
Hydronium ions
H2O
Water
Dr. R.M. Moody

31. Acids and Bases
pH is a measure of the concentration of H3O+ ions in a solution.
When [H3O+] ions = [OH-] ions, a solution is said to be neutral and has a pH of 7.
Acidic: [H3O+] ions > [OH-] ions
Basic: [H3O+] ions < [OH-] ions
Dr. R.M. Moody

32. Acids and Bases
A one-unit increase or decrease on the pH scale represents a 10-fold increase or decrease in H3O+ ions.
Acids give up H3O+ ions when dissolved in water (add them) and lower pH.
Bases accept H3O+ ions when dissolved in water and raise pH.
Pure water has a pH of 7. Rain water has a pH <7 and seawater has a pH >7
Dr. R.M. Moody

33. Buffer Systems Buffer systems control pH in living systems.
Enzymes only work in a narrow range of pHs.
Buffers are chemicals that neutralize small amounts of acid or base in solutions to maintain a neutral pH in the body.
Dr. R.M. Moody

34. Acids and Bases: Buffers
Carbonic acid and bicarbonate constitute a buffer system (e.g., your blood and seawater)
ACID
BASE