3.1.1 Atomic structure

Question 1

Where is the mass concentrated in an atom, and what makes up most of the volume of an atom?

Answer 1

• Most of the mass is concentrated in the nucleus.

- The orbitals take up most of the volume of the atom.

Question 2

Explain the terms ‘atomic number’ and ‘mass number’.

Answer 2

Atomic number:

• The number of protons in the nucleus.
• it identifies the element.

Mass number:
- The total number of protons and neutrons in the nucleus.

Question 3

Define the term ‘isotopes’ and give examples.

Answer 3

• Isotopes of an element are atoms with the same number of protons but different numbers of neutrons.
• e.g. Chlorine-35 and Chlorine-37.

Question 4

What’s the function of the mass spectrometer?

Answer 4

A mass spectrometer can tell you the relative atomic/molecular mass and the relative isotopic abundance. It can be used to identify elements.

Question 5

Define ‘first ionisation energy’.

Answer 5

The energy needed to remove 1 electron from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions.

Question 6

Explain how ions are accelerated, detected and have their abundances determined in a time of flight (TOF) mass spectrometer.
[3 marks]

Answer 6

• Ions are accelerated by attraction to the negatively charged electric field.
• Ions get detected by gaining electrons
• Abundance determined by the number of electrons gained in the detector.

Question 7

State which of the elements, magnesium and aluminium, has the lower first ionisation energy. Explain your answer.
[3 marks]

Answer 7

• Aluminium has a lower first ionisation energy…
• …because of the outer electron in 3p orbital…
• …is higher in energy/further from the nucleus, so it’s easier to remove.