Physical Properties

Question 1

What is the reason for the high melting points in giant structures like diamond, graphite, and silicon dioxide?

Answer 1

The high melting points are due to the large amount of energy needed to break the many strong covalent bonds

These structures have extensive networks of covalent bonds that require significant energy to disrupt.

Question 2

In giant ionic solids such as sodium chloride, what determines the melting points?

Answer 2

The melting points are determined by the strength of the many electrostatic forces of attraction (ionic bonds) between the cations and anions in the ionic crystal lattice

Ionic bonds are strong due to the attraction between oppositely charged ions.

Question 3

How do the melting and boiling points of simple molecular substances get affected?

Answer 3

They are affected by the strength and the relative number per molecule of the intermolecular forces, particularly hydrogen bonds

Intermolecular forces include London dispersion forces, dipole-dipole interactions, and hydrogen bonds.

Question 4

When comparing the melting and boiling points of molecular substances in the same group on the Periodic Table, what is the main factor for differences?

Answer 4

The main factor is the London forces, with exceptions for those experiencing hydrogen bonds

London forces are weak forces that occur between all molecules, while hydrogen bonds are stronger.

Question 5

What causes the differences in melting and boiling points of molecular substances of similar mass in different groups?

Answer 5

The differences are due to the presence of other intermolecular forces (dipole-dipole and/or hydrogen bonds) besides the London forces

These additional forces can significantly impact physical properties.

Question 6

In molecular substances involving hydrogen bonding, what accounts for the differences in melting and/or boiling points?

Answer 6

The differences are due to the relative number of hydrogen bonds per molecule that occur between the molecules

More hydrogen bonds can lead to higher melting and boiling points.

Question 7

Why do metals and graphite conduct electricity?

Answer 7

They conduct electricity due to the presence of delocalised valence electrons

Delocalised electrons are free to move, allowing electrical conductivity.

Question 8

When do ionic compounds conduct electricity?

Answer 8

Ionic compounds conduct electricity only when molten or in aqueous solution, i.e. when the ions are free

In solid form, ions are fixed in place within the crystal lattice and cannot conduct electricity.