Chemistry of Life Matter Occupies space and has mass Mass How much matter an object has Weight Force of gravity pulling on an object

Elements and Atoms Elements Cannot be broken down into simpler kinds of matter More than 100 exist Fewer than 30 are important to life

Atoms and Molecules Atom: The smallest unit of an element having all the characteristics of that element Electrons: negative, orbit around the nucleus, almost no mass Protons: positive, in nucleus, mass of 1 Neutrons: neutral, in nucleus, mass of 1

Atoms and Molecules Molecules The smallest particle of a substance that retains the properties of the substance; composed of two or more atoms

What do you remember from Junior High Science? Atomic Number: Number of protons Mass Number: Protons + Neutrons Ion: + or - charged atom Isotope: Atoms of the same element with different numbers of neutrons (and therefore different masses)

Bohr Model of the Atom (This model is out-of-date, but still useful for basic chemistry…) What to remember: Up to 2 e- in the first shell 8 e- in the next two shells This is what the “new” model looks like:

Ionic Bonds When one atom donates e- to another atom. Leads to + and - charged atoms Attracted to each other Overall, the molecule is neutral

Covalent Bonds When atoms SHARE e- to form a neutral molecule Methane

So how do scientists think the UNIVERSE began?

The formation of Earth… Molten gases and materials cooled Made of atoms with different weights Some sank; some floated to surface

Life Life formed on the surface from the less dense elements.

Most common biological bonds in nature… 96% of all living matter is composed of: H, O, N, and C

Stable or Unstable? For molecules composed of H, O, N, and/or C, just count the covalent bonds. Correct number? STABLE Wrong number? UNSTABLE O=O O=C=O-H STABLEUNSTABLE