Unit 1 Section 1: Atomic Structure

Question 1

What 3 particles are atoms made of?

Answer 1

• Protons
• Electrons
• Neutrons

Question 2

Where is most of an atom’s mass concentrated?

Answer 2

The nucleus

Question 3

What is found in the nucleus of an atom?

Answer 3

Protons and neutrons

Question 4

Fill in the blanks of the table.

Answer 4

Question 5

What is the atomic number of an atom?

Answer 5

The number of protons in the nucleus

Question 6

What is the mass number of an atom?

Answer 6

The total number of protons and neutrons in the nucleus of the atom.

Question 7

How do atoms form ions?

Answer 7

By gaining or losing electrons.

Question 8

What is an isotope?

Answer 8

Different forms of the same element with the same number of protons but different number of neutrons.

Question 9

a) How many protons does an atom of aluminium have?
b) How many electrons does an atom of aluminium have?
c) How many neutrons does an atom of aluminium have?

Answer 9

a) 13
b) 13 ( atoms have same amount of protons and electrons unless ionised)
c) 27 - 13 = 14

Question 10

Calcium has the nuclear symbol: (see photo)
It forms Ca^2+ ions.
a) How many electrons does a Ca^2+ ion have?
b) How many neutrons does a Ca^2+ ion have?

Answer 10

a) 20 - 2 = 18
b) 40 - 20 = 20

Question 11

(1) What was Dalton’s model of the atom?

(numbers in front indicate which theories were developed first, e.g Dalton’s theory first, Thomoson’s theory discovered next)

Answer 11

• Atoms were solid spheres
• Different spheres make up the different elements

Question 12

(2) What was Thomson’s model of the atom?

Answer 12

• Plum pudding model
• Atoms are spheres of positive charge* with embedded electrons

*hadn’t discovered protons at this point in time

Question 13

(3) What was Rutherford’s model of the atom?

Answer 13

• Alpha gold particle experiment
• Fired alpha particles at thin sheet of gold
• Most of the particles passed through the sheet
• A very small number were deflected backwards
• Concluded that there’s a tiny, positively charged nucleus at the centre,
• surrounded by a ‘cloud’ of negative electrons

Question 14

(4) What was Bohr’s model of the atom?

Answer 14

• Electrons exist in shells
• Each shell has a fixed energy
• When an electron moves between shells, electromagnetic radiation has been emitted or absorbed
• Because the shell energies are fixed, the radiation will have a fixed frequency

Question 15

Definition of relative atomic mass in terms of carbon-12.

Answer 15

• Average mass of an atom of an element
• on a scale where an atom of carbon-12 is exactly 12

Question 16

Definition of relative isotopic mass.

Answer 16

• Mass of an atom of an isotope of an element
• on a scale where an atom of carbon-12 is exactly 12

Question 17

Definition of relative molecular mass (Mr).

Answer 17

• Average mass of a molecule
• on a scale where an atom of carbon-12 is exactly 12

Question 18

Find the relative molecular mass of the following elements:
a) Rubidium
b) Mercury
c) Zinc

Answer 18

a) 85.5
b) 200.6
c) 65.4

Question 19

Magnesium has 3 isotopes. Find the RAM of magnesium.

Answer 19

1) (24 x 78.7) + (25 x 10.1) + (26 x 11.2) = 2432.5
2) 78.7 + 10.1 + 11.2 = 100
3) 2432.5/100 = 24.325
RAM of Mg = 24.3

Question 20

Label the four stages of TOF mass spectroscopy.

Answer 20

1) Ionisation
2) Acceleration
3) Ion drift
4) Detection

Question 21

Name the two types of ionisation when ionising in a TOF mass spectrometer.

Answer 21

Electron impact ionisation - for elements and low Mr compounds
Electrospray ionisation - for high Mr compounds (e.g. proteins)

Question 22

Describe how molecules are ionised using electron impact ionisation.

Answer 22

• Sample is vaporised
• ‘Electron gun’ fires high energy electrons at sample
• Knocks one electron off each particle, so they become +1 ions

Question 23

Describe how molecules are ionised using electrospray ionisation.

Answer 23

• Sample is dissolved in a solvent
• Injected through needle at high pressure
• High voltage is applied to needle, causing each particle to gain an H+ ion
• Solvent is then removed, leaving a gas made up of positive ions