7 Periodicity

Question 1

How are the elements in the periodic table arranged?

Answer 1

Elements are arranged in order of increasing atomic number, so each successive element has atoms with one extra proton

Question 2

How are the groups arranged?

Answer 2

Vertical columns
Each element in a group has atoms with the same number of outer-shell electrons, and hence similar chemical properties

Question 3

How are periods arranged?

Answer 3

Horizontal rows
Number of the period gives the number of the highest-energy electron shell of the element’s atoms

Question 4

Define periodicity

Answer 4

Repeating trends in properties of the elements

Question 5

Give the 2 descriptions of the periodic table

Answer 5

• The arrangement of elements in periods showing repeating trends in physical and chemical properties (periodicity)
• The arrangement of elements in groups having similar chemical properties

Question 6

Explain the periodic trend in electron configurations across Period 2

Answer 6

• Each period starts with an electron in a new highest-energy shell
• Across Period 2, the 2s sub-shell fills with 2 electrons, then the 2p sub-shell fills with 6

Question 7

Explain the periodic trend in electron configurations across Period 3

Answer 7

• Across Period 3, the 3s sub-shell fills with two electrons, then the 3p sub-shell fills with six i.e. the same pattern of filling is repeated (periodicity)

Question 8

Explain the periodic trend in electron configurations across Period 4

Answer 8

Although the 3d sub-shell is involved, the same pattern is repeated in the n = 4 shell, which is the highest energy energy shell

Question 9

Describe and explain the trends down a group

Answer 9

Each element has the same number of electrons in its outer shell, and hence the same number in each sub-shell within that shell
This similarity in electron configuration gives elements in the same group their similar chemistry

Question 10

What are the blocks and how are they divided?

Answer 10

Grouped in blocks corresponding to the highest energy sub-shell occupied by electrons
s, p, d and f

Question 11

Define first ionisation energy

Answer 11

The energy required to remove 1 electron from each atom in 1 mole of gaseous atoms of an element to form one mole of gaseous 1+ ions

Question 12

What is the general equation for first ionisation energy and give an example for sodium

Answer 12

X (g) –> X+ (g) + e-
Na (g) –> Na+ (g) + e-

Question 13

What are the 3 main factors that affect the ionisation energy?

Answer 13

Atomic radius
Nuclear charge
Electron shielding

Question 14

How does the atomic radius affect ionisation energy?

Answer 14

The greater the distance between the nucleus and the outer-shell electrons, the weaker the attraction to the nucleus

Question 15

How does the nuclear charge affect ionisation energy?

Answer 15

The greater the number of protons in the nucleus, the greater the attraction between the nucleus and outer electrons

Question 16

How does the electron shielding affect ionisation energy?

Answer 16

Inner shell electrons repel outer-shell electrons, creating a shielding effect that reduces the attraction between nucleus and outer electrons

Question 17

Would the helium first ionisation energy or second ionisation energy be greater?

Answer 17

Second
- 2 protons attracting 2 electrons in the 1s sub-shell
- Once one has been lost, 2 protons attract just 1 electron and the single electron feels a greater attraction to the nucleus
-Therefore more energy is required to remove the 2nd electron

Question 18

What happens if there is a big jump in ionisation number after a certain ionisation number?

Answer 18

The element is in that group e.g. jump after ionisation number 3 means in group 3 (3 electrons in its outer shell) so element in aluminium

Question 19

What is the trend in first ionisation energy down a group?

Answer 19

Ionisation energy decreases
- Atomic radius increases
- Nuclear charge increases
- Electron shielding increases
Weaker nuclear attraction

Question 20

What is the trend in first ionisation energy across a period?

Answer 20

Stronger nuclear attraction, so ionisation energy increases
- Atomic radius decreases
- Nuclear charge increases
- Electron shielding stays the same

Question 21

Compare the first ionisation of magnesium and aluminium

Answer 21

Aluminium less than magnesium
-Aluminium’s electron is in a 3p sub-level which is higher in energy than the 3s outer electrons in magnesium
- The 3p is slightly shielded by the complete 3s subshell so requires less energy

Question 22

Compare the first ionisation energy of phosphorus and sulfur

Answer 22

Sulfur less than phosphorus
- The highest energy electron in both phosphorus and sulfur is in the 3p sub level. However, while in phosphorus each 3p orbital is singly occupied, in sulfur this electron is paired
Greater electron repulsion between paired electrons means less energy is required to remove one of them