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DefinitionsIon

an atom that has gained or lost one or more electrons

Cationa positively charged ion

Aniona negatively charged ion

e-

e-e-

e-e-

1s

2s

2p

3s

3p

Ener

gyEnergy Level Diagram

Sodium

e- e- e- e- e-

e- e-

It could GAIN seven electrons to become more stable. Or…

Or it could LOSE one electron to become more stable.

Ion Na+

e- e- e- e- e- e-

All physical systems

tends towards a configurat

ion of lowest energy

Sodium will LOSE

an electro

n.

e-

e-e-

e-e-

1s

2s

2p

3s

3p

Ener

gyEnergy Level Diagram

e- e- e- e- e-

ChlorineIt could gain ONE electron to

become more stable. Or…

Or it could lose SEVEN electrons to become more stable.

e-e-

e-e- e-e- e- e-

e-

e-e-

e-e-

1s

2s

2p

3s

3p

Ener

gyEnergy Level Diagram

e- e- e- e- e-

Chlorine

Gaining an electron would require the least amount of

energy!

e-e-

e-e- e-e- e- e-

Ion Cl-

Valence electronsElectrons in the outermost

s and p orbitals

These are the most reactive

e-

e-e-

e-e-

1s

2s

2p

3s

3p

Ener

gyEnergy Level Diagram

Sodium

e- e- e- e- e-

e-

Has only ONE electron in its outermost s and p orbitals.

Therefore, it has one valence electron.

e-

e-e-

e-e-

1s

2s

2p

3s

3p

Ener

gyEnergy Level Diagram

e- e- e- e- e-

Chlorine

e-e-

e-e- e-e- e-

Has SEVEN electrons in its outermost s and p orbitals.

Therefore, it has seven valence electrons.

Lewis dot

structures

An easier way to draw the valence electrons is through…

Sometimes atoms get together and one or more electrons jumps

from one atom to another…

…this causes both atoms to have opposite charges (ions)…

…which then causes these ions to be attracted to each other.

Ionic Bond

For example…

Chlorine has a greater attraction for electrons than

Sodium

But why?Electronegativity / Chlorine = catcher

Ionic bondsOccur between metals and nonmetals

Like Sodium and Chlorineor

Potassium and Fluorine

In an ionic bond, electrons are first lost or gained, resulting in the formation of ions.

FK

FK

FK

FK

FK

FK

FK+_

Potassium (K+) ion[cation]

Fluoride (F-) ion[anion]

An ionic bond forms from the attractionbetween the positive K+ ion

and the negative F- ion

FK+_

An ionic bond forms from the attractionbetween the positive K+ ion

and the negative F- ion

The compound potassium fluoride (KF) consists of potassium (K+) ions

and fluoride (F-) ions

Ionic Bonds Properties of Ionic

Compounds

Electrons are exchanged

Ions are formed

Ions “stick together” magnetically to form

compound

Formed between metals and nonmetals

Electronegativity difference >1.7

Cation + Anion = “salt”

Forms crystals (ordered arrangements of ions)

Conduct electricity when dissolved or melted

High melting/boiling points

Hard and brittle

Rarely burn

Formation is always exothermic

Covalent BondsProperties of Covalent

Compounds

Electrons are shared

No ions are formed

Formed between two nonmetals

Electronegativity difference is

minimal

Low melting and boiling points

Typically soft and squishy

Usually do not dissolve in water as well as ionic

compounds

Don’t conduct electricity

Sometimes burn

Covalent bondsOccur between two nonmetals

Like Hydrogen and Chlorineor

Chlorine and Chlorine

In covalent bonding, atoms still want to achieve the lowest energy level possible (which means filling up all eight of their

valence seats.)

But rather than losing or gaining electrons, atoms now SHARE an

electron pair.

All physical systems

tends towards a configurat

ion of lowest energy

Covalent bonds

attempt to fill up all eight of

their valence seats…

Just like noble

gases!

Cl2

Chlorine forms

acovalent bond

withitself

ClClHowwilltwo

chlorine

atomsreact?

Each chlorine atom wants to gain one

electron to fill all of its seats.

ClCl

Cl Cl

Cl Cl

Cl Cl

Cl ClThe octet is achieved byeach atom sharing the

electron pair in the middle.

Cl ClFull 8 seats

(octet)Full 8 seats

(octet)

Cl ClThe octet is achieved byeach atom sharing the

electron pair in the middle.

Cl ClThis is the bonding pair

It is a single bonding pair

It is called a SINGLE BOND

Single bonds are abbreviated with a dash

Cl ClThis is the bonding pair

It is a single bonding pair

It is called a SINGLE BOND

Single bonds are abbreviated with a dash

Cl Cl

circle the electrons foreach atom that completestheir octets

Single bonds are abbreviated with a dash

Cl Cl

circle the electrons foreach atom that completestheir octets

This is the chlorine molecule

Cl2

Remember: Covalent bonds occur between two nonmetals!

Covalent bonds

You know this…

…and this.But you need to learn this!

O2Oxygen can also form a covalent

bond with itself.

But it needs to form two bonds since it is in Group 6A.

How can this be done?

OO

OOEach atom has two unpaired electrons

OO

OO

OO

OO

OOBoth electron pairs are shared.

6 valence electronsplus 2 shared electrons

= full octet

OO

OO6 valence electrons

plus 2 shared electrons= full octet

Two bonding pairs,

OO

making a double bond.

OO =For convenience, the double bond

can be shown as two dashes.

OO

OO =This is the oxygen molecule,

O2

Covalent bondsPolar Covalent Bond

• Shared electrons spend more time closer to one of the bonding atoms

• For example – H20

Non-Polar Covalent Bond• Shared electrons do not spend more

time closer to one of the bonding atoms• For example – 02

Two kinds…

Polar covalent bondsShared electrons spend more time closer to

one of the bonding atoms

Oxygen

HHThe

probability distribution for shared electrons.

The electrons

spend more time

near the oxygen atom.

How can you tell if you have a polar or non-polar

covalent bond?ELECTRONEGATIVI

TYElectronegativity is the power of an atom to attract electrons

The higher the value, the more electronegative the element

Remember probability distribution?

Non-polar covalent

bondsShared electrons do not spend more time closer to one of the bonding atoms

Oxygen

The probability distribution for shared electrons is shared by

both.

Oxygen

Polar covalent bond

Non-polar covalent bond

If the electronegativity difference between the two

nonmetals is 0.3-1.7

If the electronegativity difference between the two nonmetals is less than 0.3

ReviewIonic bond• Between a metal and nonmetal• Electrons are lost/gained and the

resulting change in charge attracts the ions together

Covalent bond• Between two nonmetals• Electrons are shared between the atoms• Polar/Non-polar• Ruled by electronegativity