Atomic Structure

Question 1

What is a molecule?

Answer 1

A (small) number of atoms covalently bonded together

Question 2

What is an ion?

Answer 2

An atom (or group of atoms) that has gained or lost electrons

Question 3

What is an element?

Answer 3

A substance that contains only one type of atom

Question 4

What is a compound?

Answer 4

A compound contains two or more different types of atoms chemically bonded together (ionic or covalent)

Question 5

What is a mixture?

Answer 5

A mixture contains two or more substances (elements or compounds) that are not chemically bonded together

Question 6

Define Relative Atomic Mass

Answer 6

The weighted average mass of an atom of an element (including all isotopes) relative to 1/12 of an atom of C-12

Question 7

Define Relative Molecular Mass

Answer 7

The mass of a molecule relative to 1/12 of an atom of C-12

Question 8

What is a mole?

Answer 8

Amount of substance containing Avogadro’s constant (6.022x10^23) number of particles

Question 9

Define Molecular Formulae

Answer 9

The actual number of atoms of each element in a substance/compound

Question 10

Define Empirical Formulae

Answer 10

The simplest whole number ratio of an atom within a substance

Question 11

Define First Ionisation Energy

Answer 11

The amount of energy required to remove one mole of electrons from one mole of gaseous atoms to form gaseous ions
X(g) —> X+(g) + e-

Question 12

Define Second Ionisation Energy

Answer 12

The amount of energy required to remove one mole of electrons from one mole of a 1+ gaseous ion to form one mole of 2+ gaseous ions
X+(g) —> X2+(g) + e-

Question 13

What are the 3 factors that affect ionisation energy?

Answer 13

Shielding (amount of shells)
Nuclear Charge
Atomic Radius

Question 14

What is the trend of ionisation energies across a period

Answer 14

Ionisation energy increases because:

• more protons in nucleus (nuclear charge increases)
• atomic radius decreases (outer e- closer to positive nucleus)
• no additional shielding

Question 15

What is the trend of ionisation energies down a group?

Answer 15

Ionisation energy decreases because:

• atomic radius increases (outer e- further away from positive nucleus)
• more shielding
• nuclear charge has no effect

Question 16

Explain the deviation from the trend between beryllium + boron (also applies to Mg and Al)

Answer 16

Boron has a lower IE than Beryllium because

• Boron atom has more shielding therefore outer e- is further from the positive nucleus
• Boron’s outer e- is in a higher energy sub shell (p) than Beryllium’s outer electron which is in the s sub shell

Question 17

Explain the deviation from the trend between nitrogen + oxygen (also applies to P and S)

Answer 17

Oxygen has a lower IE than Nitrogen because:

• e- paired in 2nd p orbital
• paired e- repel
• therefore outer e- more easily lost

Question 18

What is an isotope?

Answer 18

Isotopes are atoms of the same element with a different number of neutrons

Question 19

Define ‘mass number’ of an atom

Answer 19

The total number of protons and neutrons in the nucleus