Simple molecular substances

Question 1

Atom

definition

Answer 1

The smallest part of an element that can exist.

Question 2

Charge

definition

Answer 2

Property of matter that causes a force when near another charge. Charge comes in two forms, positive and negative. For example, a negative charge causes a repulsive force on a neighbouring negative charge.

Question 3

Charged particles

Definition

Answer 3

Particles, usually ions or electrons, that carry electrical charges.

Question 4

Compound

definition

Answer 4

A substance formed by the chemical union of two or more elements.

Question 5

Covalent bond

Definition

Answer 5

A bond between atoms formed when atoms share electrons to achieve a full outer shell of electrons.

Question 6

Double bond

Definition

Answer 6

A covalent bond resulting from the sharing of four electrons (two pairs) between two atoms.

Question 7

intermolecular forces

Definition

Answer 7

Weak attractive forces between molecules. When a simple molecular substance melts or boils, it is the intermolecular forces that are broken (not the covalent bonds in each molecule).

Question 8

molecular

definition

Answer 8

Refers to a substance made up of molecules, so it contains small groups of atoms, of a set size, held together by covalent bonds.

Question 9

molecule

definition

Answer 9

A collection of two or more atoms held together by chemical bonds.

Question 10

What is a covalent bond formed between?

Answer 10

A covalent bond is formed when a pair of electrons is shared between two atoms, usually non-metals.

Question 11

What do molecules consist of?

Answer 11

A molecule consists of a group of two or more atoms joined together by covalent bonds.

Question 12

Molecule

Answer 12

A molecule consists of a group of two or more atoms joined together by covalent bonds. Molecules of the same element or compound will have a set size - in other words, they will always contain the same number of atoms of each element. For example, a molecule of methane, CH4, will always contain one carbon atom and four hydrogen atoms.

Question 13

A simple molecule can be modelled by drawing its structure.

In these structures what are atoms and covalent bonds show as?

Answer 13

show each atom by its element symbol

show each covalent bond as a straight line

Question 14

Melting and boiling points of simple molecular substances.

Answer 14

Simple molecular substances generally have low melting points and boiling points and are often liquids or gases at room temperature.

Question 15

What are melting and boiling points examples of?

Answer 15

State changes

Question 16

Describe how the forces of attraction are overcome in melting or boiling?

Answer 16

some forces of attraction are overcome during melting, allowing molecules to move over each other

more of the forces of attraction are overcome during boiling, allowing the molecules to move freely away from each other

Question 17

Comparison of strength of intermolecular forces

simple molecules and covalent bonds

reference boiling and melting points

Answer 17

There are intermolecular forces between simple molecules. These intermolecular forces are much weaker than the strong covalent bonds in molecules. When simple molecular substances melt or boil, it is these weak intermolecular forces that are overcome. The covalent bonds are not broken. Very little energy is needed to overcome the intermolecular forces, so simple molecular substances usually have low melting and boiling points.

Question 18

A substance can conduct electricity if:

Answer 18

it contains charged particles, and

these particles are free to move from place to place

Question 19

Can simple molecules conduct electricity?

Answer 19

Simple molecules have no overall charge, or charged particles that can separate, so simple molecular substances cannot conduct electricity, even when liquid or dissolved in water.

Question 20

D o simple molecules have a charge?

Answer 20

Simple molecules have no overall charge, or charged particles that can separate