Chemical Bonding• Atoms will bond together to become stable

• Atoms may share electrons to become stable

-OR-• Atoms may gain or lose electrons to

become stable.

• By gaining or losing electrons these atoms can fill or empty their outer energy level

Ionic BondingIonic bond – bond between oppositely

charged ions, involving a total transfer of electrons between atoms

Ion – a charged particle

Types of Ions

Cations - lose electrons and become positively charged

Usually metals

Anions - gain electrons and become negatively charged

Usually non-metals

The Cation (+ ion) loses an electron(s) which is transferred to the Anion (- ion) so both become stable

The now oppositely charged ions are attracted to each other due to magnetism

• A neutral atom becomes an ion either by losing an electron (cation) or by gaining an electron (anion).

• A sodium atom transfers an electron to a chlorine atom to create table salt

The transfer of the electron caused the

neutral sodium atom to become a positively

charged ion (a cation), and the neutral

chlorine atom to become a negatively charged

ion (an anion). 

• Sodium transfers an electron to chlorine

• When the transfer occurs, sodium’s valence shell is empty, making the next ring in the valence shell, which is full.

What is happening?• The one valence electron from potassium is transferred

to the iodine. Both become stable with now full outer rings. Potassium becomes positively charged (+1: lacking one electron) and Iodine becomes negatively charged (-1: one extra electron).

Multiple ions• The two valence electrons from magnesium are

transferred, one to each chlorine. All three become stable with now full outer rings. Magnesium becomes positively charged (+2: lacking two electrons) and each chlorine becomes negatively charged (-1: one extra electron).

Steps for Writing Ionic Formulas

1. Write the symbols for the ions with the cation first, and anion second.

2. Balance the charges by inserting subscripts. There must be equal numbers of positive and negative charges to balance out to zero overall charge.

3. Write the chemical formula, indicating with subscripts how many of each ion are needed to make a neutral compound.

Polyatomic Ions• Polyatomic ion – multiple atoms covalently

bonded together which, as a group, have an overall charge to become stable

• The group will lose or gain electrons to become stable.

• Act as a unit

• You cannot change subscripts of the polyatomic ion, but can have multiple of the unit.

• Examples: Hydroxide OH-

Sulfate SO42-

Phosphate PO43-

• This ion cannot be changed, but you can have more than one of the ion. Use parentheses and a subscript outside the parentheses to balance charges.

Beryllium chlorate

Be2+ ClO3-

Be2+(ClO3-)2

Multiple Charge Cations

• Some “d-block” elements are capable of forming ions with different charges

In these cases Roman numerals are used to indicate which ion / charge is used

For example copper can form +1 and +2

ions by losing either 1 or 2 electrons

Copper (I) or Copper (II)

Cu+1 Cu+2