Ionic Bonding

Question 1

Why bonding occurs

Answer 1

• All forces of attraction leading to chemical bonding between atoms are electrical in nature.
• Bonding between atoms occurs as a result of the electron structure of an atom.
• All atoms are striving to gain a full outer shell of electrons, therefore few atoms are found free in nature, (only the Noble Gases can be found free in nature).
• Normally atoms are neutral – they have no charge.
  This doesn’t necessarily mean that they are stable!
• To be stable atoms must have a full outer shell.
  Atoms are willing to sacrifice their neutrality for some stability.

Question 2

What happens in ionic bonding

Answer 2

• In an ionic bond, electrons are gained or lost. Not shared.
• The donators (the metals) lose their electrons and become cations and the acceptors (non-metals) gain these electrons and become anions. An electrostatic force of attraction (between opposite charges; + and - ) is formed, bonding the atoms strongly together, creating a crystal lattice with regular, repeating structure to achieve the most stability.

Question 3

NaCl example

Answer 3

• The typical example of an ionic compound is sodium chloride, NaCl, or common salt. In reality all ionic compounds are examples of a large group of compounds called salts.
• For this example, the sodium atoms loose their outer most electrons and become postively charged and the chlorine atoms gain these electrons to become negatively charged. The atoms collectively then bond together to form a crystal lattice.

Question 4

Ions and electronegativity

Answer 4

• Electronegativity is the measure of an atom’s ability to attract electrons.
• Electonegativity is determined by factors such as; the size of the atom, the charge on the nucleus and the number of electrons in the atom.
• It is the electronegativity of an atom that determines whether it will gain or lose electrons to form a full outer shell.
• FONCL are the most electronegative elements, fluorine being the most.

Question 5

Characteristics of the substances formed

Answer 5

• When a chemical reaction occurs, the new substance has very different properties from the substances that made it.

Question 6

Properties of salts formed- Hard, and high melting temperature.

Answer 6

• Oppositely charged ions attract each other strongly forming a lattice which is difficult to break by either scratching or heating.

Question 7

Properties of salts formed- Conduct electricity

Answer 7

• Conduct electricity when molten or dissolved.
  In solid state the ions are held in place and can’t move.
  In the molten state and when dissolved in water (aqueous) the ions can move and carry a charge.

*In order for there to be conduction of electricity there must be charged particles free to move, thus most do not conduct electricity.

Question 8

Properties of salts formed- Brittle

Answer 8

• When a force is applied, the strongly bonded lattice resists. However, eventually the ions begin to slide past each other.
• Ions of the same charge move next to each other and repulsion replaces attraction – the solid breaks.

Question 9

Naming ionic compounds

Answer 9

• When naming binary ionic compounds always name the cation first and then the anion with an –ide ending. (e.g sodium chloride).
• Use the cross over method to determine the lowest whole number ratio of ions that will give a net zero charge. E.g. Al3+ and S2- become Al2S3
• Variable charge ions use roman numerals. (e.g iron(II) oxide and iron(III) oxide). Note: the roman numeral is the charge on the ion not the number of ions present.

Question 10

Rules for naming polyatomic ionic compounds

Answer 10

• For polyatomic ions use brackets e.g. (NH4)3PO4 (There are 3 sets of NH4).

Use the prefixes given below to indicate the number of water molecules in the hydrated compound.

mono- 1         hexa- 6
di- 2               hepta- 7
tri- 3               octa- 8
tetra- 4          nona- 9
pentra- 5       deca- 10