Ionic Bonding

Ionic Bonding

Occurs when electrons are transferred from one atom

to another, forming two ions

The ions stay together because of electrostatic

attractions (btw positive & negative atoms)

Ionic bonds form easily between alkali metals and

halogens

The Octet Rule

Atoms tend to gain, share, or lose electrons in order

to obtain a full set of valence electrons (in most cases

this equals 8)

An octet of electrons consists of full s and p sublevels on

an atom.

Exceptions: transition elements and rare earth elements

Example

Na + Cl Na + Cl+ -

Properties of Ionic Compounds

Ionic compounds do not

form molecules; they form a

crystal lattice

The green spheres are Na+

and the red spheres are Cl -

This is a crystal of

CaCl2. Each ion is

held rigidly in

place by strong

electrostatic

forces that bond it

to several

oppositely

charged ions

Other Properties

Normally form between metals and nonmetals

Ionic compounds have ions that form very strong bonds, which makes them hard and brittle

They have high melting points and high boiling points

When dissolved in water, the solution will conduct electricity

Types of Ions

There are two types of ions

Monatomic: cation or anion that consists of a single atom.

Examples: Na+ and Cl-

Polyatomic: two or more atoms that act as a single ion (or

particle). Examples: (CO3)2- and (OH)-

Types of Ionic Compounds

Ionic compounds will be a combination of

a metal and a nonmetal (if the cation is

monatomic)

There are two types of ionic compounds

Binary Ionic Compounds: contains the ions of

only two elements (NaCl, CaCl2)

Polyatomic Ionic Compounds: contain at least

one polyatomic ion (CaCO3, Mg(OH)2)

The names DO NOT indicate the ratio of

ions present, but the formulas do

Names of Charged Particles

When electrons are lost, the ion has an overall positive charge and is called a cation Examples: Na+, Ca2+

When electrons are gained, the ion has an overall negative charge and is called an anion Examples: F-, S2-

The negative ions will attract the positive ions and form a bond

All ionic compounds are electrically neutral

Ionic ChargesMonatomic ionsIons that consist of only one atom

Charges often can be determined by using the periodic table

Many of the transition metals have more than one chargeThe charge on the ion is indicated by using a Roman

numeral next to the name of the element

• Cu has a 1+ and a 2+ charge. Cu 1+ is called Copper I, and Cu2+ is called Copper II

A few transition metals have only one charge

The names of these do not have to include a Roman

numeral

• Zn, Cd

Monatomic Ions

Group Atoms that

commonly form

ions

Charge on

ions

1 H, Li, Na, K, Rb, Cs 1+

2 Be, Mg, Ca, Sr, Ba 2+

13 B, Al 3+

15 N, P, As 3-

16 O, S, Se, Te 2-

17 F, Cl, Br, I 1-

Ionic Compounds

Writing formulas for binary ionic

compounds

Compounds composed of two elements are

called binary compounds

When the formula is written, the charge of the

cation must be balanced by the charge of the

anion

The overall charge of the ion combination must be

zero

The cation is always written first in the formula

Writing Formulas for Ionic Compounds

To write the formula for an ionic compound:

Write the chemical symbol and overall charge of the cation or polyatomic cation: Na+, Ca2+, NH4

+

Write the chemical symbol and overall charge of the anion or polyatomic anion: Cl-, O2-, NO3

-

Add the charges

If equal, write the chemical symbols together, e.g. NaCl, CaO, NH4NO3

If not equal, crisscross values of the charges and make them subscripts, e.g. Ca(NO3)2, CaCl2

Crisscross Method (also called “Drop and Swap”

Na+ can combine with S2-

The value of the charge on Na, which is 1, becomes the subscript

for S: S

The value of the charge on S, which is 2, becomes the subscript

for Na: Na2

The resulting formula is Na2S

Naming Ionic Compounds

Naming binary ionic compoundsIt is important to know the Stock naming system

and the charges on cations before naming ionic compounds

The process is the reverse of writing formulas

Polyatomic ionic compounds

Compounds that contain atoms of three different elementsThey usually contain a polyatomic ion; must be recognized first to be able

to name the compound correctly

Tightly bound groups of atoms that behave as a unit and carry a charge

Have the suffix –ite and –ate

• These ions will be given to you on a sheet; you will not have to memorize them

• Hydroxide and cyanide are the only common polyatomic ions that end in –ide

Common Polyatomic Ions

Ion Name Ion Name

NH4+ Ammonium NO2

- Nitrite

NO3- Nitrate OH- Hydroxide

CO32- Carbonate SO4

2- Sulfate

O22- Peroxide C2H3O2

- Acetate

SO32- Sulfite ClO3

- Chlorate

You will get these on a chart for tests and quizzes!!

How Do I Write the Formulas for

Polyatomic Ions?

Put parentheses around any polyatomic

ion and add subscripts to the outside of

the parentheses.

Never change the subscript of a

polyatomic ion (it will change the

composition of the ion):

Ca(OH)2, Ca3(PO4)2

Include the subscript inside the parentheses

Practice

Sodium combines with fluorine

Chlorine combines with hydrogen

The nitrite ion combines with calcium

The ammonium ion combines with nitrogen