3.1.1.3 Electron configuration

Question 1

What are energy levels?

Answer 1

Electrons have fixed energies, they move around the nucleus in regions called energy levels.

Question 2

Which electrons have the lowest energy?

Answer 2

The ones closest to the nucleus (energy level 1)

Question 3

What is an orbital?

Answer 3

A region of space where we are likely to find an electron.
Each orbital holds 2 electrons

Question 4

What is the Aufbau principle?

Answer 4

Electrons enter the lowest available energy level

Question 5

What is the Pauli exclusion principle?

Answer 5

Each orbital may contain no more than two electrons, provided the two electrons are spinning in opposite directions

Question 6

What is Hund’s rule?

Answer 6

Single electrons occupy all empty orbitals within a sub-shell before they start to form pairs in orbitals

Question 7

What are the special case electron configurations of copper and chromium?

Answer 7

For chromium, the d-sub shell is half filled ([Ar]3d5 4s1)
For copper its 3d sub shell is fully filled ([Ar]3d10 4s1)

Question 8

What is the shape of the s-orbital?

Answer 8

Sphere

Question 9

What is the shape of the p-orbital?

Answer 9

Dumb-bell
can be drawn in the x, y or z plane.
(all will have same energy)

Question 10

What is the first ionisation energy?

Answer 10

The enthalpy change to remove 1 mole of electron from 1 mole of gaseous atoms to form 1 mole of gaseous ions with a +1 charge

Question 11

What is the second ionisation energy?

Answer 11

The enthalpy change to remove 1 mole of electrons from 1 mole of gaseous ion with a +1 charge to form 1 mole of gaseous ion with +2 charge

Question 12

What is the sequence of ionisation energies?

Answer 12

The successive ionisation energies needed to remove electrons from an atom until only the nucleus is left.

Question 13

What are the factors that affect ionisation energies?

Answer 13

Nuclear charge (proton number)
Atomic number
Shielding effect

Question 14

How does nuclear charge affect ionisation energy?

Answer 14

More protons = greater charge
More positively charged nucleus so the outer electrons are strongly held by the nucleus.
So more energy to remove outer electron.

Question 15

How does atomic radius affect ionisation energy?

Answer 15

Bigger atom = outer electrons are further from the nucleus.
So weaker attraction between nucleus and outer electrons.
So less energy to remove outer electrons.

Question 16

How does atomic radius change across a period?

Answer 16

For atoms, across a period radius decreases.
For + ions, radius decrease.
For - ions, radius increase

Question 17

How does the shielding effect influence ionisation energy?

Answer 17

An electron in an outer shell is repelled by inner shells.
More shielding = weaker attraction between outer electrons and nucleus, so less energy to remove outer electrons.

Question 18

What is the general pattern for ionisation energy across a period?

Answer 18

General increase (small drops between group 2 and 3, and group 5 and 6)

Question 19

Describe the general increase in ionisation energy across the first period

Answer 19

Nuclear charge increasing
Atomic radius decreasing
Shielding effect similar
So nuclear attraction increases

Question 20

Describe the drops in ionisation energy between grp 2 and 3

Answer 20

Outer electrons for Grp 3 in 3p sub shell, but for Grp 2 in 3s sub shell. 3p electrons higher in energy so easier to remove. 3p are also slightly shielded by 3s electrons.

Question 21

Describe the drops in ionisation energy between grp 5 and 6

Answer 21

For grp 6 the presence of paired electrons in 3p sub-shell leads to electron repulsion, which makes it easier to remove electrons

Question 22

Describe the pattern for ionisation energy down a group

Answer 22

Decrease
- Shielding effect increases (extra inner shell)
- Atomic radius increase (outer electron further from nucleus)
- , so weaker nuclear attraction