Ionic Bonding

Students know atoms combine to form molecules by sharing electrons to form covalent or metallic bonds or by exchanging electrons to form ionic bonds.

Students know salt crystals, such as NaCl, are repeating patterns of positive and negative ions held together by electrostatic attraction.

Bonds Forces that hold groups of

atoms together and make them

function as a unit.

Ionic bonds – transfer of electrons

Covalent bonds – sharing of electrons

The Octet Rule – Ionic Compounds

Ionic compounds form so that each atom, by gaining or losing electrons, has an octet of electrons in its highest occupied energy level.

Metals lose electrons to form positively-charged cations

Nonmetals gains electrons to form negatively-charged anions

Ionic Bonding:The Formation of Sodium

Chloride

Sodium has 1 valence electron

Cl: 1s22s22p63s23p5

Na: 1s22s22p63s1

Chlorine has 7 valence electrons

An electron transferred gives each an octet

Ionic Bonding:The Formation of Sodium

Chloride

Cl- 1s22s22p63s23p6

Na+ 1s22s22p6

This transfer forms ions, each with an octet:

Ionic Bonding:The Formation of Sodium

Chloride

Cl- Na+

The resulting ions come together due to electrostatic attraction (opposites attract):

The net charge on the compound must equal zero

Ionic Bonds

Metal to NonmetalHigh END

Metal forms cationNonmetal forms anion

Sodium Chloride Crystal Lattice

Ionic compounds form solid crystals at ordinary temperatures.Ionic compounds organize in a characteristic crystal lattice of alternating positive and negative ions.All salts are ionic compounds and form

crystals.

Ionic solids are brittle

+ - + -+- +-

+ - + -+- +-

Force + - + -

Strong repulsion breaks crystal apart.

Visual Concept

Characteristics of Ion Bonding in a Crystal Lattice

Properties of Ionic Compounds

Structure: Crystalline solids

Melting point:

Generally high

Boiling Point:

Generally high

Electrical Conductivity:

Excellent conductors, molten and aqueous

Solubility in water:

Generally soluble

Lattice Energy- the ionic bond

---the energy released when the crystal lattice formation is formed

---Lattice energies are listed as negative values to indicate that energy is given off when ions come together to form the ionic crystal.

The greater the lattice energy… the stronger the ionic bonding!

Vocabulary

COMPOUND

ternarycompound

binarycompound

2 elementsmore than 2

elements

NaNO3NaCl

Vocabulary

ION

polyatomicIon

monatomicIon

1 atom 2 or more atoms

NO3-Na+

e-

3p+

lithium atomLi

e-

loss of one valence

electron

e-

e-

lithium ionLi+

3p+e-

e-

9p+

fluorine atomF

e-

e-

e-

e-

e-

e-

e- e-

e-

gain of one valence

electron

fluoride ionF1-

9p+e-

e-

e-

e-e-

e-

e-

e-

e-

e-

e-

Formation of Cation

3p+

lithium atomLi

e-

loss of one valence

electron

e-

e-

lithium ionLi+

3p+e-

e-

e-

Formation of Anion

9p+

fluorine atomF

e-

e-

e-

e-

e-

e-

e- e-

e-

e-

gain of one valence

electron

fluoride ionF1-

9p+e-

e-

e-

e-e-

e-

e-

e-

e-

e-

Formation of Ionic Bond

fluoride ionF1-

9p+e-

e-

e-

e-e-

e-

e-

e-

e-

e-

lithium ionLi+

3p+e-

e-

Ionic bonding: Li + Cl1e-

3p+

4n02e- 17p+

18n08e-8e-2e 3p+

4n02e-1e- 17p

+18n07e- 8e- 2e-

Li Cl [ Cl ]–

[Li]+

lithium atom chlorine atom lithium ion chloride ion

Ionic bonding: Li + C

Li + Cl [ Cl ]–[Li]+

Ionic compound formation equation

Ionic bonding: Mg + O

12p+

12n02e- 8e- 2e-

1e-

[ O ]2–

[Mg]2+

6e- 2e-

8n0 8p+

1e-

8e- 2e-

8n0 8p+ 12p+

12n02e- 8e-

OMg

Lewis Dot Diagrams and

BONDING (Ionic )

How do we show the valence electrons for different elements?

* dot diagrams were developed by American, G.N. Lewis, in the 1920's* they are called Lewis structure or Lewis dot diagrams

Electron-Dot Notation

To keep track of valence electrons, it is helpful to use electron-dot notation.

Electron-dot notation shows only the valence electrons of an atom of a particular element, indicated by dots placed around the element’s symbol. The inner-shell electrons are not shown.

Click below to watch the Visual Concept.

Visual Concept

Electron-Dot Notation

Hydrogen has one valence electron

Nitrogen has five valence electrons.

Mg

Write the electron dot diagram for

• Na• Mg• C• O• F• Ne• He

1s22s22p63s1

1s22s22p63s2

1s22s22p2

1s22s22p4

1s22s22p5

1s22s22p6

1s2

Na

C

O

F

He

Ne

Ionic Bonding

Na Cl

transfer of electron

+1 -1

NaCl

Ca +2

P -3Ca

+2

P

• All the electrons must be accounted for!

+2

Ionic Bonding

Ca -3

Ionic Bonding

Ca3P2Formula Unit

Ca2+

Ca2+

Ca2+

P3-

P 3-

Ca2+

P3- Ca2+

P3-

Ca2+

Ionic Formation Equation

Ca

P + 2[ P ]–33[Ca]

+2

* monatomic ions can be written with dot diagrams

* as before, dots are used to demonstrate e-

* symbol is in [brackets] to represent ions

* charge is placed on the upper right corner

Do the dot diagrams for Na, Mg, Al, P, S, Cl ions

+1

-1

PracticeDraw the Lewis Dot Diagrams

for the following compounds:1. Lithium iodide2. Calcium chloride3. Potassium oxideExample: Magnesium Chloride

[Mg]+22[ Cl ]-1

Polyatomic Ions

An example of a polyatomic ion is the ammonium ion: . It is sometimes written as to

show that the group of atoms as a whole has a charge of +1.

The charge of the ammonium ion is determined as follows:

seven protons in the nitrogen atom plus the four protons in the four hydrogen atoms give the ammonium ion a total positive charge of

+11.

When nitrogen and hydrogen atoms combine to form an ammonium ion, one of their electrons is lost, giving the polyatomic ion a total negative charge of -10.

The total charge is therefore (+11) + (-10) = +1.

Some examples of Lewis structures of polyatomic ions are shown below.