Periodicity and Group 1 Elements

Question 1

DEFINE ATOMIC RADIUS:

Answer 1

• the average distance from the nucleus to valence electron(s)
• usually expressed in pm (10^−12 m).

Question 2

WHAT IS THE TREND OF ATOMIC RADIUS DOWN A GROUP/ ACROSS A PERIOD?

Answer 2

• atom radius increases down a group
• atomic radius decreases across the period
  NOTE: the smaller the atomic radius, the stronger the attraction between the valence electrons and nucleus

Question 3

WHY DOES THE RADIUS INCREASE DOWN A GROUP AND WHAT ARE THE EFFECTS?

Answer 3

1. shielding increases since there are more electrons
2. an extra energy level is added -> electrons with higher principal number
   - therefore, nucleus attracts valence electrons less strongly.

Question 4

WHY DOES THE RADIUS DECREASE ACROSS THE PERIOD AND WHAT ARE THE EFFECTS?

Answer 4

1. an additional electron is added to the same energy level - shielding remains the same.
2. there is an extra proton inside the nucleus each time, therefore increasing the nuclear charge.
   - increase in effective nuclear charge -> tighter grip on valence electron.

Question 5

DEFINE FIRST IONISATION ENERGY:

Answer 5

• the energy required to remove one mole of valence electrons from one mole of gaseous atoms to produce 1 mole of gaseous ions each with a charge of +1.
  e. g., Na(g) –> Na+(g) + e-

Question 6

ABOUT FIRST IONISATION ENERGY:

Answer 6

• E1 is always endothermic
• the higher the energy value (more +ve), the more energy required for ionisation.
• this is because the valence electrons are more tightly held by the nucleus.

Question 7

WHAT IS THE TREND OF IONISATION ENERGY DOWN A GROUP?

Answer 7

• ionisation decreases (less endothermic).

- valence electrons are less tightly held by the nucleus.

Question 8

WHY DOES IONISATION ENERGY DECREASE DOWN A GROUP?

Answer 8

• each time, valence electron goes in higher energy level - shielding and atomic radius increases.
• these outweigh the effect of the increase in the nuclear charge.

Question 9

WHAT IS THE TREND OF IONISATION ENERGY ACROSS A PERIOD?

Answer 9

• overall, the ionisation energy increases.

- valence electrons are more tightly held by the nucleus.

Question 10

WHY DOES IONISATION ENERGY INCREASE ACROSS A PERIOD?

Answer 10

• each time, valence electron remains in the same energy level - shielding remains constant, nuclear charge increases while atomic radius decreases.

Question 11

DEFINE ELECTRON AFFINITY:

Answer 11

• change in energy when a gaseous neutral atom accepts an electron to form a negative ion (per mol).
• 1st electron affinity is nearly always exothermic.

Question 12

WHAT IS THE TREND OF ELECTRON AFFINITY ACROSS A PERIOD?

Answer 12

• shielding remains the same, atomic radius decreases, nuclear charge increases.
• therefore, atom has greater appetite to gain an electron.

Question 13

WHAT IS THE TREND OF ELECTRON AFFINITY DOWN A GROUP?

Answer 13

• shielding is increased, and so is atomic radius, both of theme overcome the increased nuclear charge.
• hence the atom has a lesser propensity to gain an electron.

Question 14

DEFINE ELECTRONEGATIVITY:

Answer 14

• a tendency for an atom to attract electrons to itself.

Question 15

WHAT IS THE TREND OF ELECTRONEGATIVITY ACROSS A PERIOD/ DOWN A GROUP?

Answer 15

• increases across a period, decreases down a group.

- reasoning is same as EA.