1.2.1 - Electron Structure

Question 1

Rearrange the sub-shells in terms of relative energies starting with the smallest first:

• 2s
• 1s
• 3d
• 3s
• 3p
• 4s
• 4p
• 2p

Answer 1

• 1s
• 2s
• 2p
• 3s
• 3p
• 4s
• 3d
• 4p

Question 2

State the number of electrons that occupy the:

• s sub-shell.
• p sub-shell.
• d sub-shell.
• t sub-shell.

Answer 2

• s sub-shell = 2 max.
• p sub-shell = 6 max.
• d sub-shell = 10 max.
• t sub-shell = 14 max.

Question 2

1. An iron atom has 26 electrons. Deduce its electron configuration.
2. The 4s-electrons are lost before the 3d-electrons. Write the electron configuration for Fe²⁺ ion.

Answer 2

1. 1s², 2s², 2p⁶, 3s², 3p⁶, 4s², 3d⁶
2. 1s², 2s², 2p⁶, 3s², 3p⁶, 3d⁶

Question 3

Describe the shape of an s-orbital and describe how this differs from a p-orbital.

Answer 3

• S orbitals have a spherical shape.
• P orbitals have a 3D dumb-bell shape with the nucleus in the centre.

Question 6

Give three factors that can influence ionisation energies.

Answer 6

• Nuclear charge.
• Electron shielding.
• Distance from the electrons to the nucleus.

Question 7

State the number of electrons that can fill the first four shells.

Answer 7

• 2
• 8
• 18
• 32

Question 7

The element Mg has 12 electrons. Deduce the electron configuration.

Answer 7

1s², 2s², 2p⁶, 3s²

Question 8

Describe what an orbital is.

Answer 8

Orbital - a region of space that can hold up to two electrons with opposite spins.

Question 9

State the number of orbitals making up these sub-shells:

• s
• p
• d
• t

Answer 9

• s - 1 orbit
• p - 3 orbits
• d - 5 orbits
• t - 7 orbits.

Question 10

Define the terms:

• First ionisation energy.
• Sucessive ionisation energy.

Answer 10

• First ionisation energy - The energy required to remove one electron from each atom in a mole of gaseous atoms.
• Sucessive ionisation energy - The energy required to remove one electron from each ion in a mole of gaseous 1+ ions.

Question 11

Explain how the atomic raduis can influence ionisation energies.

Answer 11

The greater the atomic radius, the lower the ionisation energy. This is because the nuclear attraction is smaller between the nucleus and the outer-shell electrons and therefore is easier to remove an electron.