Transcript The Chemical Basis of Life

The Chemical Basis of Life
Chapter 4
Matter
Anything that occupies space.
 Composed of one or more chemical
elements.

Examples?
Element vs. Compound

Element: A pure substance that can not be
broken down into other substances by
chemical means.

Compound: Composed of two or more
elements that are chemically combined in
a fixed ratio.
4 elements make up 96% of living matter in
your body.
They are:
O – Oxygen
H – Hydrogen
C – Carbon
N – Nitrogen
Examples
Iron is an Element: Fe
Water is a compound:
H 2O
Salt is a compound: NaCl
+
=
Different elements have different
properties

These properties are based on the
structure of their atoms.
Atoms

Are made up of subatomic particles
Protons
 Neutrons
 Electrons

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Atomic Number
The number of protons in an atom
 All atoms of the same element have the
same atomic number.

Electrons and Reactivity

An atom’s electrons determine its
reactivity.

There are different energy levels
surrounding the nucleus into which
electrons are placed.
1st Energy Level
Closest to the nucleus
 Holds 2 electrons

2nd Energy Level

Holds 8 electrons
The energy levels closest to the nucleus
 Having partially filled energy levels is what
makes atoms reactive.
 Carbon:

Draw models for:
Neon (10 electrons)
Nitrogen (7 electrons)
Lithium (3 electrons)
Which atom(s) is/are reactive? Which is/are
not as reactive?
Ionic Bonds
When an
atom
transfers an
electron to
another atom.
Example:
 Lithium
 Lithium
Fluoride (LiF)
(3 electrons) +
Flourine (9 electrons)
Ionic Bonds (continued)
When the electron moves from one atom
to another, the atoms now become
charged (ions).
 What are the charges on each atom?

Li (+)
 F (-)


What happens now with these two ions?
Covalent Bonds
When two atoms share electrons
 Stronger than an ionic bond

Structure of Water

H & O covalently bonded together.

Water is polar

It has a slightly positive charge on one end
and a slightly negative charge on the other.