Mr

UNIT I

CHEMISTRY/BIOCHEMISTRY

I. CHEMISTRY: THE BASIS FOR LIFE

A. ELEMENTS

Almost everything around us can be broken down into simpler substances. These substances can be

further broken down into other simpler substances. There is a point where substances can no longer be

broken down into other substances while keeping their characteristic properties. These substances are

called elements. There are currently 106 named elements (92 naturally occurring), but this number is

increasing because more man made elements are being created in laboratories.

From these 92 naturally occurring elements, only 20 are necessary for life. Of these 20 life elements, 6

make up 99% of all living matter: Sulfur, Phosphorous, Oxygen, Nitrogen, Carbon and Hydrogen

(SPONCH, pneumonic device). Living organisms still need the other 14 elements, but in smaller

amounts.

An atom is the smallest indivisible unit of an element that still has the characteristic of the element. Two

or more atoms can combine chemically and form a molecule. A compound is any pure substance that

contains two or more different atoms.

Atom = H Molecule = H

2

Compound = H

2

O

B. FORMS OF MATTER

Atoms, elements and compounds are forms of matter. Matter can come in one of three states on the earth:

1. Solid

Has definite shape and has a definite volume

2. Liquid

Has no definite shape but has a definite volume

3. Gas

Has no definite shape and has no definite volume

C. SUBATOMIC PARTICLES

Atoms can be broken down into smaller components called subatomic particles: protons, neutrons, and

electrons. Protons and neutrons make up the nucleus of an atom. They are roughly equal in mass, one

atomic mass unit (amu) or Dalton. Protons are positively charged and neutrons are not changed. Electrons