Why Atoms Combine?

Intro to Bonding

Elements

Made from only one type of atom.•example: Oxygen (O2)

Helium (He)

CompoundsMade from more than one type of atom, more than one element

Compounds always have exactly the same ratio of the elements of which it is made

The COMPOUND WATER, (H2O) always has 2 hydrogen and 1 oxygen

Compounds

Compounds–Compounds have properties different

than those of the elements of which they are made •ex: table salt, NaCl is made of a poisonous metal and a poisonous gas

Neutral Atom

• What does neutral mean?– Number of electrons surrounding the nucleus is

equal to the number of protons– Neutral, but not always happy

How many protons does Li have?

How many total electrons does Li have?

How many valence (outer) electrons does Li have?

3

3

1

Is Li happy by itself?

No. It doesn’t have a full outer shell

How many protons does O have?

How many total electrons does O have?

How many valence (outer) electrons does O have?

8

8

6

Is O happy by itself?

No. It doesn’t have a full outer shell

How many protons does He have?

How many total electrons does He have?

How many valence (outer) electrons does He have?

2

2

2Is He happy by itself?

Yes! It has a full outer shell

Chemically Stable Atoms

Chemically Stable Atoms–Have outer electron energy levels that are

full•The maximum numbers of electrons that can be in that shell are in that shell –For example, 2 electrons in the first, 8 in

the second, etc.

Chemically Stable Atoms

Chemically Stable Atoms•The number of electrons in outer (sub)energy level is found on the periodic table

Chemically Stable Atoms

1

23

4

5

6

7 8

Chemically Stable AtomsDot diagrams show the number of electrons in an outer energy

level: The chemical symbol for the atom is surrounded by the number of

dots corresponding to the number of electrons in outer energy level.

Valence Electrons

1 2 3 4 5 6.. 7 8

Group Alkali Alkaline Boron Carbon Nitrogen Oxygen Halogens Noble Gases

Example Hydrogen Calcium Aluminum Silicon Arsenic Sulfur Fluorine Neon

H. .Ca..

.Al. .

.Si.

.

...As.

.

...S.

..

..:F .

..

..:Ne:

..

Chemically Stable Atoms

–Elements with eight or zero dots are chemically stable •Noble gases are naturally chemically stable•Noble gases don’t form compounds naturally (called “inert”).

Chemically Stable Atoms

–All other elements have incomplete outer shells (1 to 7 electrons) and lose, gain, or share electrons to make their outer shells "full" and become chemically stable.

Chemical Bonds

• A chemical bond is the way elements combine to form compounds–A bond is a force of attraction between

elements– It is the result of the process in which they lose,

gain, or share electrons to make their outer shells "full".

Ions

• Ions are atoms or molecules that have a charge (+ or -) –They have gained or lost electrons

in order to fill their outer energy level–Therefore protons ≠ electrons