Unit 1: Chapter 3 - Trends in the Periodic Table

Question 1

What is a measure of atomic size?

Answer 1

A measure of atomic size is the atomic radius, which is a measure of HALF THE DISTANCE between the nuclei of two bonded atoms of the element.

Question 2

How can the inter-nuclear distances be measured?

Answer 2

The inter-nuclear distances can be measured using X-ray diffraction, where the nuclei are observable but the electron clouds are not.

Question 3

What is the unit of measurement in the picometre?

Answer 3

10-12 metres

Question 4

In a period of the table, what do all of the elements have?

Answer 4

The same number of electron shells.

Question 5

What do the number of increase by one going across a period?

Answer 5

The number of electrons and protons.

Question 6

As the positive charge of the nucleus increases (like it does across a period) what happens to the atom?

Answer 6

As the positive charge of the nucleus increases, it exerts an increasing attraction to the outer shell of electrons and PULLS them closer to the nucleus. This has the affect of decreasing the atomic radii of the elements as you move move from left to right across a period.

Question 7

What is the general trend across period 2 in atomic radii?

Answer 7

The general trend across period 2 is a decrease in atomic radii.

Question 8

What do we see as we go down a group in the periodic table?

Answer 8

As we go down a group in the periodic table we see that the outer shell contains the same amount of electrons but a NEW SHELL IS BEING ADDED EACH TIME.

Question 9

What affect does having an extra shell have on the atom?

Answer 9

This has the affect of reducing the attraction of the positive nucleus to the outer electrons as MORE ELECTRON SHELLS are added each time. Known as the “Shielding Effect”.

Question 10

As the attraction is reduced as each new shell is added, how does this effect atomic radii?

Answer 10

The atomic radii increases down groups.

Question 11

What is the 1st ionisation energy?

Answer 11

The 1st ionisation energy is the energy per mole required to remove one electron from the outer shell of an atom in the gaseous state.

Question 12

What is the 2nd ionisation energy?

Answer 12

The 2nd ionisation energy is the energy per mole required to remove the second electron from the same atom as the 1st ionisation energy in he gaseous state.

Question 13

What is the unit for ionisation energy?

Answer 13

Kj mole-1

Question 14

In the formation of an ionic bond, what is one important factor?

Answer 14

The energy change in creating positive ions from neutral isolated atoms, i.e. atoms considered to be in the GASEOUS STATE.

Question 15

In period 2 what is the general trend across the period?

Answer 15

In period 2 the general trend is an increase in ionisation energies.

Question 16

What is the general trend in ionisation in periods across a period?

Answer 16

The general trend is an increase in energy required.

Question 17

Why is the general trend in ionisation energies an increase in energy required?

Answer 17

This is due to the POSITIVE NUCLEAR CHARGE IN THE NUCLEUS INCREASING going across a period. As a proton is added to each nucleus an electron is being added to the SAME SHELL. This BINDS THE OUTER ELECTRONS TIGHTER TO THE NUCLEUS as the charge increases and making it more difficult to remove an electron.

Question 18

Why is the 2nd ionisation energy value for Lithium and Sodium really high?

Answer 18

The high 2nd ionisation energy value for Lithium and Sodium is due to having to break into a full shell of electrons to remove a second electron.

Question 19

What is the general trend in ionisation energies going down a group?

Answer 19

The general trend is a decrease in the energy required for 1st and 2nd ionisation.

Question 20

What is the general trend in ionisation energy going down group 2?

Answer 20

The general trend is a decrease in the energy required for 1st and 2nd ionisation.

Question 21

Why is the general trend going down a group a decrease in ionisation energies required?

Answer 21

This is due to the “Shielding Effect”, where the increase in the number of electron shells, as we move down a group, shields the outer electrons from the positive charge on the nucleus. As the NUMBER OF SHELLS INCREASE, the HOLD ON THE OUTER ELECTRONS DECREASE as they move further away from the nucleus. Thus making it easier to remove the outer electron.

Question 22

What elements have greater ion character?

Answer 22

Those with a greater ionisation energy difference.

Question 23

What is meant by the term electronegativity?

Answer 23

Electronegativity is the measure of attraction an atom/nucleus has for the electrons in a bond/shared electrons.

Question 24

What is the range of values for electronegativity?

Answer 24

Values range from 0 to 4 (Pauling scale).

Question 25

In a diatomic what will the more electronegative atom attract towards itself?

Answer 25

The more electronegative atom will attract the bonding electrons towards itself.

Question 26

What do you get if the electronegativities of the atom in a molecule differ greatly?

Answer 26

A polar covalent molecule.

Question 27

What is an example of a polar molecule?

Answer 27

HCL, hydrogen chloride.

Question 28

Why is HCL a polar molecule?

Answer 28

The electronegativity value for chlorine is considerably higher than hydrogen. Therefor the chlorine has a stronger attraction to the bonding electrons. The bonding electrons thus move closer to the chlorine atom leaving hydrogen slightly positive and making chlorine slightly negative. This movement results in HCL being a polar molecule.

Question 29

What happens to the electronegativity values across a period?

Answer 29

They increase.

Question 30

Why does electronegativity increase across a period.

Answer 30

This is due to the increase in the positive nuclear charge in the nucleus. Which increases the attraction for the binding electrons.

Question 31

What happens to the electronegativity values going down a group?

Answer 31

Electronegativity decreases going down a group.

Question 32

Why does electronegativity decrease going down a group?

Answer 32

This is due to the increase in the size of the atoms as a new shell of electrons is being added each time otherwise known as the “Shielding Effect”. This means the distance between the nucleus and outer electrons, which decreases the “pull” the nucleus has on the bonding electrons.