Ionic bonding and structure

Question 1

What is ionic bonding?

Answer 1

The transfer of one or more electrons from the outer shell of one atom to the outer shell of another atom. Ions form as a result.

Question 2

How do cations form?

Answer 2

When metallic atoms lose electrons, they have more protons than electrons and become positively charged. Valence electrons are lost, resulting in a positive ion.

Question 3

How do anions form?

Answer 3

When non-metallic atoms gain electrons, which means they have more electrons than protons and become negatively charged.

Question 4

What are ionic bonds and what difference in electronegativity is required?

Answer 4

• An electrostatic attraction between oppositely-charged ions (positive and negative ions).
• Ionic bonds are formed by elements with an electronegativity difference of 1.8 units and greater.

Question 5

What is electrostatic attraction?

Answer 5

The force of attraction between opposite charges. They also exist between positive nuclei and bonding electrons.

Question 6

What makes up ionic compounds, what is an exception and give an example of an ionic compound?

Answer 6

• They are composed of a metal and non-metal element
• There are exceptions e.e.g ammonium chloride
• Sodium is a metal and has low ionization energy (energy required to lose an electron) and therefore loses a valence electron to form a cation
• It then has a noble gas configuration (1s2 2s2 2p6)
• Chlorine forms an anion and also a noble gas configuration
• The octet rule states that atoms are more stable with a noble gas configuration

Question 7

Give 3 details about the structure of an ionic compound.

Answer 7

• Ions are arranged in a regular crystalline structure called lattice structure
• They are solids under normal conditions
• Ionic bonding is described as being non-directional, as the force of attraction occurs in all directions around the individual ions

Question 8

What are poly-atomic ions?

Answer 8

• Ions that consist of more than one atom
• The atoms that make up the poly-atomic ion are bonded by covalent bonds (intramolecular forces)
• The bonding between two ions is ionic (intermolecular forces)

Question 9

Name the 9 poly-atomic ions and their charges.

Answer 9

OH- (hydroxide)
NO3- (Nitrate)
NO2- (Nitrite)
HCO3- (Hydrogen carbonate)
CO3 2- (Carbonate)
SO4 2- (Sulfate)
SO3 2- (Sulfite)
PO4 3- (Phosphate)
NH4 + (Ammonia)

Question 10

What is the charge of an ionic compound?

Answer 10

• There is no overall charge (neutral) and the charges of the ions cancel out

Question 11

Explain the boiling/melting points and volatility of ionic compounds?

Answer 11

• High melting and boiling point as the electrostatic attraction is strong which means a large amount of energy is required to break these forces of attraction. Ionic compounds are solid under standard conditions.
• Have a very low volatility (how easily a substance evaporates), due to the strong forces of attraction in the lattice

Question 12

Explain the solubility in ionic compounds.

Answer 12

• Generally highly soluble in water (e.g. group 1 ions and group 7)
• The solubility depends on the forces of attraction between the water molecules and the ions in the lattice structure. Ions are separated by hydration, so that the solid dissolves
• Because water is polar, the partial charges are attracted to the oppositely-charged ions in the lattice structure, the ions break off
• If the attraction between water molecules and ions in the lattice are strong enough to overcome the attraction between the ions themselves, the compound is soluble
• Non-polar solvents cannot disrupt the lattice in the same way, the solubility of ionic substances in solvents such as hexane is limited

Question 13

Explain the electrical conductivity and brittleness of ionic compounds.

Answer 13

• Depends on the presence of mobile ions
• Ionic compounds do not conduct electricity when solid because the ions are held in a fixed position. When molten or dissolved, the ions are free to move and carry an electric current
• They fracture across a plane when the layers of ions become incorrectly aligned. When force is applied, ions of the same charge are placed next to each other
• The forces of repulsion between ions of the same charge cause the lattice structure to split and fracture

Question 14

How do you know how many electrons must be lost or gained based on the electron configuration?

Answer 14

When an element has a noble gas configuration, it has a full p6 sub-orbital. When it has more or less than p6, it can be deduced how many electrons it needs to lose or gain in order to become stable.