Make An Ionic Model! Formative Assessment

True or false?

Calcium fluoride has a greater ratio of anions to cations than sodium fluoride.

• True
• False

Answer explanation

The chemical formula of calcium fluoride is CaF₂ and the chemical formula of sodium fluoride is NaF. The ratio of anions to cations is 2:1 for CaF₂ and is 1:1 for NaF.

Ionic compounds form a three-dimensional ________ structure.

State which substance has the strongest ionic bonds.

• KF

• CaF₂

• KCl

• CaCl₂

Answer explanation

The substance with the smaller ionic radius and greater ionic charge will have the stronger ionic bonds. Looking first at the cations, since Ca²⁺ has a greater ionic charge than K⁺, the stronger ionic bond must be one of the compounds containing calcium. Looking at the anions, since F^– has one fewer occupied energy levels than Cl^–, it has a smaller ionic radius. Therefore, CaF₂ has the strongest ionic bond.

State which of the following have an impact on the strength of the ionic bond.

I.   Ionic radius
II.  Number of neutrons
III. Charge of the ion

• I, II, and III

• I and III

• I and II

• II and III

Answer explanation

The smaller the ionic radius and the greater the ionic charge, the stronger the ionic bond. While the number of neutrons will influence the mass of the ions, it will have no influence on the strength of the ionic bond. This is because neutrons are neutral and the strength of the ionic bond depends on factors that influence the strength of the electrostatic attraction between oppositely charged ions.

True or false?

In solid magnesium bromide, the ratio of magnesium ions to bromide ions is 2:1. 

• True

• False

Answer explanation

The ratio of Mg²⁺ ions to Br⁻ ions is 1:2, but there is more than one Mg²⁺ ion and two Br⁻ ions. Many ions bond together to form a three-dimensional, repeating lattice.

Which of the following explains why ionic compounds are solids under standard conditions?

I.   strong electrostatic attraction between oppositely charged ions
II.  ions arranged in a 3D lattice structure
III. delocalised electrons stabilising the structure 

• I and III

• I, II, and III

• II and III

• I and II

Answer explanation

The strong electrostatic attraction between oppositely charged ions arranged in a 3D lattice is responsible for the high melting points of ionic compounds.

Ionic compounds do not have delocalised electrons in the structure.