Energy & Stability

• Rubberbands

• Springs

• Kleenex box

• Popper

High Energy means Low Stability.High Energy means Low Stability.

Low Energy means High Stability.Low Energy means High Stability.

Stability in Chemical Systems

• If it exists, it’s stable!

• Of course, some things are more stable than others.

Noble Gases – What they tell us

• Group 18 or Group VIIIA or Group O.

• Do notnot form compounds under ordinary conditions. They are extremely stablestable.

• All have 8 valence electrons: great All have 8 valence electrons: great stability. Must also be low energy!stability. Must also be low energy!

Why do atoms gain or lose electrons?

• They are trying to get the structure of the nearest noble gas!

• What’s the nearest noble gas to – F– Na– S– Mg– H

Ne – the F adds 1 electron It’s still Ne – the Na loses 1 electron

Ar – the S adds 2 electrons

Ne – the Mg loses 2 electrons

He – the H adds 1 electron

Octet Rule

• When we say that atoms are trying to get an octet, we mean …

They are trying to attain the electron structure of the nearest noble gas.

Strictly speaking, H wants only a duet.

Lewis Structures of Atoms

• Use dots around the symbol to represent the valence electrons.

• What’s the Lewis structure for Cl?

• For Ca?

.Cl:

:

:

Ca·

·

s-block p-block

Gain or Lose?

• Atoms form ions to get to the nearest noble gas configuration.

• Metals tend to have 1, 2, or 3 valence electrons. It’s easier to lose 1, 2, or 3 than gain 5, 6, or 7.

• Remember – it’s all or nothing!

Metals: Atoms to Ions

• Na: 2-8-1 2-8-0, Na+1

• K: 2-8-8-1 • Mg: 2-8-2

• Al: 2-8-3 • Ca: 2-8-8-2 • Cs: 2-8-18-18-8-1

2-8-8-0, K+1

2-8-0, Mg+2

2-8-0, Al+3

2-8-8-0, Ca+2

2-8-18-18-8-0, Cs+1

Lewis Structures for Positive Ions

Na atom, 2-8-1: Na·

Na+1, 2-8-0: [Na]+1

• The ions always have square brackets and a charge. • Lewis diagram of the ion has to reference the same shell as the Lewis diagram of the atom.

Lewis Structures for Positive Ions

• Mg atom, 2-8-2

Mg.

• Mg+2, 2-8-0

[Mg]+2

• Al atom, 2-8-3

Al·

• Al+3, 2-8-0

[Al]+3

··

.

What do they have in common? No Dots!

Gain or Lose?

• Nonmetals tend to have 5, 6, or 7 valence electrons. It’s easier to add 1, 2, or 3 than lose 5, 6, or 7.

Nonmetals: Atoms to Ions

• S: 2-8-6 2-8-8, S-2

• F: 2-7 • N: 2-5 • Br: 2-8-18-7 • Se: 2-8-18-6 • P: 2-8-5

2-8, F-1

2-8, N-3

2-8-18-8, Br-1

2-8-18-8, Se-2

2-8-8, P-3

Lewis Structures for Negative Ions

F atom, 2-7: .F:

F-1, 2-8: [:F:]-1

Try S-2 and N-3

What do they have in common?

::

::

8 DOTS!

Noble Gases

• They already have 8 valence electrons, except He which has 2.

• They don’t form ions very easily.

How many valence electrons

• Group 1 or IA• Group 2 or IIA• Group 13 or IIIA• Group 14 or IVA• Group 15 or VA• Group 16 or VIA• Group 17 or VIIA• Group 18 or VIIIA

Predict Likely Charges

• Ba

• Te

• I

• Rb

• Sr

• O

• Kr

• Cs

• Ra

• Br

• N

• B

+2-2

-1

+1+2

-2

0+1

+2

-1-3

+3

Ionic Size Relative to Parent AtomIonic Size Relative to Parent Atom

• Depends on if it’s a positive ion or a Depends on if it’s a positive ion or a negative ion.negative ion.

• How do you make a positive ion?How do you make a positive ion?

• How do you make a negative ion?How do you make a negative ion?

Remove electronsRemove electrons

Add electronsAdd electrons

Size of Ions

• Positive ion - smaller than the parent atom.

• Not only do you remove electrons, you wipe out a whole shell!

• Negative ion – larger than the parent atom.

• Trying to jam an extra electron into the cloud. Adds lots of repulsions.

Metals are losers!

• Metals lose electrons to form positive ions or cations.

• Cations are always smaller than the parent atom.

Nonmetals are winners!

• Nonmetals gain electrons to form negative ions or anions.

• Anions are always larger than the parent atom.