Electrons in atoms

Question 1

Electronic configuration

Answer 1

a way of representing the arrangement of the electrons in atoms showing the principal quantum shells, the sub-shells and the number of electrons present

Question 2

Ionisation energy

Answer 2

the energy change that accompanies the process of firing high-speed electrons at atoms to work out how much energy has to be supplied to form an ion by knocking out one electron from each atom

Question 3

First ionisation energy

Answer 3

the energy needed to remove 1 mole of electrons from 1 mole of atoms of an element in the gaseous state to form 1 mole of gaseous ions

Question 4

Successive ionisation energies

Answer 4

the energy required in each step to remove the first electron, then the second, then the third, etc… from a gaseous atom

Question 5

Factors that influence ionisation energy

Answer 5

• atomic radius
• nuclear charge
• shielding/screening effect
• spin-pair repulsion

Question 6

Atomic radius

Answer 6

• atomic radius increase
• ionisation energy decreases
• less energy required to overcome the force of attraction

Question 7

Nuclear charge

Answer 7

charge an atom will possess because of its positively charged nucleus

• nuclear charge increases
• attractive forces between nucleus & outermost electrons increases
• ionisation energy increases
• more energy is required to overcome the attractive forces

Question 8

Shielding / Screening effect

Answer 8

outermost electron is shielded from the nuclear charge by the inner electrons or shells

• no of shells / inner electrons increases
• ionisation energy decreases

Question 9

Shielding

Answer 9

the ability of inner shell electrons to reduce the effect of the nuclear charge on outer shell electrons

Question 10

Sub-shells ( subsidiary quantum shells )

Answer 10

A sub-shell is a division of electron shells (energy levels) in an atom. Each sub-shell consists of orbitals, which are regions around the nucleus where electrons are likely to be found.

Question 11

Atomic orbitals

Answer 11

the region in space where there is the maximum probability of finding an electron

Question 12

s-block

Answer 12

elements in group 1&2 having outermost electrons in an s-sub-shell

Question 13

p-block

Answer 13

elements in group 13-18 having outermost electrons in a p-sub-shell

• exception : He

Question 14

d-block

Answer 14

elements that add electrons in the d-sub-shell

-> transition elements

Question 15

Spin-pair repulsion

Answer 15

electrons in the space repel each other because they have the same charge

• spins are opposite to minimise repulsion

Question 16

Free radicals

Answer 16

a species with one or more unpaired electrons

Question 17

Atomic radius down a group

Answer 17

• increases
• each successive element has one more shell of electrons further away from the nucleus

Question 18

Atomic radius across a period

Answer 18

• decreases
• number of protons increases
• nuclear charge increases by one in each successive element

Question 19

What is the order of filling energy sublevels (s, p, d, f) in electron configuration?

Answer 19

1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p < 6s < 4f < 5d < 6p < 7s < 5f < 6d < 7p.

Question 20

What are the common exceptions to the predicted electron configurations, and why do they occur?

Answer 20

Exceptions occur in elements like chromium ([Ar] 4s¹ 3d⁵) and copper ([Ar] 4s¹ 3d¹⁰) due to the stability gained by half-filled and fully-filled d-subshells.