Ionic Bonding

What is an ion? How is it formed?

An ion is an electrically charged atom or group of atoms formed by the loss or gain of electrons

Why are ions formed?

This loss or gain of electrons takes place to obtain a fullouter shell of electrons

When are negative ions (anions) formed? How many electrons are there in relation to protons then?

• Negative ions are formed when atoms gain electrons, meaning they have more electrons than protons

When are positive ions (anions) formed? How many electrons are there in relation to protons then?

Positive ions are called cations and form when atoms lose electrons, meaning they have more protons than electrons

What type of charge do metal ions form?

All metals lose electrons to other atoms to become positively charged ions

What type of charge do non metal ions form?

• All non-metals gain electrons from other atoms to become negatively charged ions

How are positive and negative ions/charges held together?

The positive and negative charges/ions are held together by the strong electrostatic forces of attraction between oppositely charged ions

What do dot and cross diagrams display?

• These show the arrangement of the electrons in an ionic compound

• The electrons are shown as dots and crosses

• The charge of the ion is spread evenly which is shown by using brackets

• The charge on each ion is written at the top right-hand corner

How can you tell the charge of an ion in a dot and cross diagram?

The number of electrons that an atom gains or loses is the same as the charge.

Describe the ionic bonding in sodium chloride from this dot and cross diagram

• Sodium is a Group 1 metal so loses one outer electron to another atom to gain a full outer shell of electrons

• A positive sodium ion with the charge 1+ is formed, Na+ 

• Chlorine is a Group 7 non-metal so gains one electron to have a full outer shell of electrons

• A negative chloride ion with a charge of 1- is formed, Cl –

• The ions are then attracted to one another and held together by electrostatic forces

The formula of the ionic compound is thus NaCl

Describe the ionic bonding in magnesium oxide from this dot and cross diagram

• Magnesium is a Group 2 metal so will lose two outer electrons to another atom to have a full outer shell of electrons

• A positive ion with the charge 2+ is formed, Mg2+ 

• Oxygen is a Group 6 non-metal so will need to gain two electrons to have a full outer shell of electrons

• Two electrons will be transferred from the outer shell of the magnesium atom to the outer shell of the oxygen atom

• Oxygen atom will gain two electrons to form a negative ion with charge 2-

• The ions are then attracted to one another and held together by electrostatic forces

• The formula of the ionic compound is thus MgO

How would you find the formula of an ionic compound in a dot and cross diagram?

• If it is a dot-and-cross diagram, then just count the number of atoms of each element

• This is then equal to the empirical formula of the compound

How would you find the formula of an ionic compound in a 3D lattice structure?

• If it is a 3D lattice structure, then look for how many ionsare in the lattice

• Write them down and balance the charges to find the formula for the compound

What 5 things do you have to do when describing ionic bonding?

• State how many electrons the metal loses

• State the resulting charge of the metal ion

• State how many electrons the non-metal gains

• State the resulting charge of the non-metal ion

• State that the oppositely charged ions are held together by strong forces of attraction in ionic bonding