1. Chemistry of Life
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Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

2. Nature’s building materials
Atoms
Nature’s building materials
All things (including cells) are made of atoms
We must understand chemistry in order to understand living things
Life processes include chemical reactions.
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

3. Any substance that has mass and occupies space is known as matter.
Atoms
Mass is the measurable amount of a substance. It is usually measured in grams or kilograms
Any substance that has mass and occupies space is known as matter.
Composed of atoms.
electrons (-) in orbitals surrounding a nucleus
nucleus formed of protons (+) and neutrons (no charge).
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

4. Raven - Johnson - Biology: 6th Ed
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

5. Mass - Amount of a substance.
Atoms
Mass - Amount of a substance.
Weight - Force gravity exerts on a object.
Atomic number – Number of protons
Atomic Mass - Equal to the sum of masses of protons and neutrons.
Measured in daltons (mass units).
Protons and neutrons both weigh approximately 1 dalton
Electrons weigh 1/1840 of a dalton (very light weight!).
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

6. Atoms
Atoms with the same atomic number have the same chemical properties.
Atoms of an element that possess a different number of neutrons are called isotopes.
Some are unstable, radioactive
As they give off radioactive energy, they decay
Half life – time for ½ of material to decay
Example: 14C has a half life of 5600 years.
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

7. Number of electrons determines the chemical properties of an atom
Atoms
Electrons –
Number of electrons determines the chemical properties of an atom
Atoms with the same number of protons and electrons are electrically neutral
Electrons are maintained in orbits by their attraction to the positively charged nucleus
Ions - Atoms in which the number of electrons does not equal the number of protons.
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

8. Chemical Behavior of Atoms
Orbital - Area around a nucleus where an electron is most likely to be found.
Because electrons are attracted to the nucleus, it takes energy to maintain them in orbitals.
Electrons have potential energy due to their relative position.
Example: grapefruit in hand vs. grapefruit on top of tall building
Example: During photosynthesis, sunlight excites electrons in chlorophyll molecules and pushes them away from the nucleus.
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

9. Raven - Johnson - Biology: 6th Ed
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

10. Give rise to discrete molecules.
Covalent Bonds
Covalent bonds form when two atoms share one or more pairs of valence electrons
Give rise to discrete molecules.
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies