Chemistry of Life Copyright © McGraw-Hill Companies Permission required for reproduction or display Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

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

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

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

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

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

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

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

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

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