Atom Stability* In order for atoms to be stable, they need

to have their outer energy level completely filled.

* In most cases, atoms need to have 8 valence electrons in their outer energy level (8 is great).

* Atoms with 8 valence electrons are said to have octets.

• The Noble Gases (group 18) naturally have octets and are said to be chemically stable. All other atoms must either lose or gain electrons to become stable.

• There are 2 exceptions to the octet rule: Hydrogen which will lose one electron to be stable and Helium which has a full outer shell with 2 electrons (because it only has 1 energy level)

Electron Losers & Gainers• Atoms want to become stable by doing the

least amount of work possible.

• Consider the following analogy:

You are sitting at a table all by yourself. 7 of your friends are sitting at the table next to you. From a work standpoint (not popularity), will it be less work for you to join your 7 friends or all 7 of your friends to join you?

Of course, from a work standpoint, it takes less work for you to join your friends.

Who gains, who loses??• Is it easier for group one atoms to lose their 1

valence electron or to gain 7more?

Group 1 = Lose 1 electron

• Is it easier for group two atoms to lose their 2 valence electrons or to gain 6 more?

Group 2 = Lose 2 electrons

• Is it easier for group thirteen atoms to lose their 3 electrons or to gain 5 more?

Group 13 = Lose 3 electrons

• Is it easier for group fourteen atoms to lose 4 valence electrons or to gain 4 more?

Group 14 = Lose 4e- or Gain 4e-

• Is it easier for group fifteen atoms to lose 5 valence electrons or to gain 3 more?

Group 15 = Gain 3 electrons

• Is it easier for group 16 atoms to lose 6 valence electrons or to gain 2 more?

Group 16 = Gain 2 electrons

• Is it easier for group seventeen atoms to lose 7 valence electrons or to gain 1 more?

Group 17 = Gain 1e-

In general, metals are electron losers and non-metals are electron gainers

Ions vs. Atoms• After an atom has lost or gained

electrons, it becomes an ion. An ion will have a positive or a negative charge.

• In an atom, the number of protons is equal to the number of electrons.

a) The number of positive charges equals the number of negative charges.

b)The overall charge of any atom is ZERO.

• Example: Lithium• An atom of lithium has 3 protons and 3

electrons

An atom of lithium is electrically neutral because the (+) = (-), however, it is unstable

+

++

e

e

eValence electron

This energy level can hold 8 electrons, it needs 7 more to be stable

• Lithium will lose its 1 valence electron to become stable. Once Lithium loses its 1 valence electron, the number of (+) = (-)

• Now lithium has 1 more (+) than (-). Lithium has become an ion with a charge of 1+. Written as Li1+

++

+

e

e

Now, Lithium has a complete outer energy level. Lithium is now stable

• Example: Fluorine

• An atom of fluorine has 9 protons and 9 electrons.

• An atom of fluorine is electrically neutral; however, it is unstable

++

+

+

+

++

++

e

e

e

e

e

e

e

This energy level can hold 8 electrons, it needs one more to become stable

e

e

• Fluorine will gain 1 electron to become stable. Once fluorine gains an electron, the number of (+) = (-)

• Now, fluorine has 1 more (-) than positive. Fluorine has become an ion with a charge of 1- Written as F1-

++

+

+

+

++

++

e

e

e

e

e

e

e

e

e

e

Now, fluorine has a complete outer shell.

Metals

* All atoms that lose electrons and form positive ions are called cations.

* All metals form cations

* Metals are electron losers

+ +

Non - metals

* All atoms that gain electrons and form negative ions are called anions.

* All non-metals form anions.

* Non-metals are electron gainers

- -

• End day One Here!

Bonding • Atoms become stable by transferring or

sharing electrons with other atoms.

• Ionic Bonds are formed between oppositely charged ions

a) transfer electrons

b) occur between metals and non-metals

NaCl (salt)

c) Conduct electricity when dissolved in water

Covalent Bonds• Defined as the force of attraction between the

nuclei of atoms and the electrons shared by the atoms.

a) occur between non-metals

b) tend to

1) have low boiling points

2) have low melting points

3) brittle in the solid state

c) Two types of covalent bonds

1) non-polar atoms share electrons equally ex:F2

2) polar atoms do not share electrons equally

ex: H2O Oxygen has a stronger pull for the electrons. The Oxygen end will have a slight negative charge and the

Hydrogen end will have a slight positive charge.

O -

H + H +

• Covalently bonded atoms are called molecules.

• Molecules are defined as a neutral group of atoms held together by covalent bonds

• Diatomic Molecules – two atoms covalently bonded together.

1) Seven elements exist as diatomic molecules naturally: Hydrogen, Oxygen, Nitrogen, Fluorine, Chlorine, Bromine, Iodine

Lewis Dots

• Model that only shows the valence electrons.

• How to draw Lewis Dots:

1) Write the symbol of the atom

Mg

2) Image 4 boxes around the symbol

Mg Mg

Each box can only hold two electrons. Place dots in the boxes to represent the number of valence electrons.

Draw the Lewis Dot Representations for the following:

• Sodium Chlorine

• Calcium Bromine

• Oxygen Beryllium

• Carbon Potassium

• Hydrogen Lithium

• Nitrogen

• Aluminum

• Fluorine

Draw Lewis Dots showing how the following pairs will bond

1) Lithium and Bromine2) Potassium and Sulfur3) Calcium and Iodine4) Magnesium and Fluorine5) Sodium and Oxygen6) Beryllium and Chlorine7) Lithium and Oxygen8) Sodium and Sulfur9) Calcium and Oxygen10)Magnesium and Chlorine