1.5 solid structures

Question 1

ionic solids

Answer 1

Ionic solids (crystals) are giant lattices of positive and negative ions made up of oppositely charged ions packed around each other.

Question 2

sodium chloride

Answer 2

each Na+ cation is surrounded by six Cl- anions and each Cl- anion is surrounded by six Na+cations.

Question 3

sodium chloride coordination number

Answer 3

6:6

Question 4

caesium chloride

Answer 4

Cs+ cations pack around a Cl- ion. Similarly 8, Cl- anions pack around a Cs+ cation.

Question 5

caesium chloride coordination number

Answer 5

8:8

Question 6

difference in the crystal coordination numbers

Answer 6

Cs+ cation is larger than the Na+, so has more room to accommodate a greater number of anions.

Question 7

properties of ionic compounds

Answer 7

determined by the strength of the electrostatic forces between the ions

Question 8

high melting and boiling temperatures

Answer 8

it takes a large amount of energy to overcome the strong electrostatic forces between the oppositely charged ions.

Question 9

often soluble in water

Answer 9

the oxygen end of the water molecules is attracted to the positive ions, and the hydrogen ends of the water molecules are attracted to the negative ions.

Question 10

hard but brittle

Answer 10

when force is applied, layers of ions slide over each other causing ions of the same charge to be next to each other; the ions repel each other and the crystal shatters.

Question 11

poor electrical conductivity when solid, but good when molten or dissolved

Answer 11

in the solid state, the ions are fixed in position by the strong ionic bonds; however, when molten or dissolved, the ions are free to move and will move to the electrode of opposite charge, so will carry the current.

Question 12

what is meant by the term allotropes?

Answer 12

the different forms are called allotropes; they possess different structural forms of the same element.