EL - Periodic trends

Question 1

What does the periodic table arrange elements by?

Answer 1

By atomic number.

Question 2

How does the periodic table group elements?

Answer 2

Groups elements with similar properties together.

Question 3

What are the rows of the periodic table called?

Answer 3

Periods.

Question 4

What are the columns of the periodic table called?

Answer 4

Groups.

Question 5

What do all elements within a period have the same number of?

Answer 5

Electron shells.

Question 6

What does the period number tell you about?

Answer 6

The number of electron shells an element has.

For example, elements in period 1 have one electron shell and elements in period 5 have 5 electron shells.

Question 7

What do all elements in the same group have the same number of?

Answer 7

Electrons in their outer shell.

Question 8

What does the group number tell you about an element?

Answer 8

The number of electrons in the outer shell.

For example, group 1 elements have 1 electron in their outer shell and group 6 elements have 6 electrons in their outer shell.

Question 9

What is the exception in the fact that the group number refers to the number of electrons in the outer shell?

Answer 9

Group 0 elements have a full outer shell - 8 electrons.

Question 10

What can you say about the properties within a group?

Answer 10

Elements in the same group have similar physical and chemical properties.

Question 11

How do properties differ within a group?

Answer 11

Change gradually as you go down the group.

For example, group 1 metals become more reactive as you go down the group, whereas group 7 elements become gradually less reactive.

Question 12

What 2 periods show similar trends in their melting points?

Answer 12

2 and 3

Question 13

For the metals (Li and Be, Na, Mg and Al), what happens to melting points across the period?

Answer 13

Increases

Question 14

Why does the melting point of the metals increase across the period?

Answer 14

Because the metal-metal bonds get stronger. This is because the metal ions have an increasing number of delocalised electrons and a decreasing ionic radius. This leads to a higher charge density which attracts the ions together more strongly.

Question 15

What does an increase in strength of metal-metal bonds and a decreasing ionic radius lead to?

Answer 15

A higher charge density which attracts the ions together more strongly.

Question 16

How does the size of the molecule/number of atoms in a molecule affect melting point?

Answer 16

More atoms = stronger intermolecular forces = higher mp.

Question 17

Which group of elements have the lowest melting point and why?

Answer 17

The noble gases (Ne and Ar) as they exist as individual atoms (they’re monatomic) resulting in a very weak intermolecular force.

Question 18

What is ionisation?

Answer 18

The removal or one or more electrons.

Question 19

What happens to an atom when electrons have been removed?

Answer 19

The atom’s been ionised.

Question 20

What is the energy you need to remove the first electron from an atom called?

Answer 20

First ionisation enthalpy.

Question 21

What is the first ionisation enthalpy?

Answer 21

The energy needed to remove 1 electron from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions.

Question 22

What must you include when writing equations for ionisations?

Answer 22

The gas state symbol (g).

Question 23

Why must you use the gas state symbol (g) when writing ionisation equations?

Answer 23

Because ionisation enthalpies are measured for gaseous atoms.

Question 24

How many atoms do you refer to when working out an ionisation enthalpy?

Answer 24

1 mole of atoms.

Question 25

The lower the ionisation enthalpy…

Answer 25

The easier it is to remove an outer electron and form an ion.

Question 26

What 3 things affect the size of ionisation enthalpies?

Answer 26

Atomic radius
Nuclear charge
Electron shielding

Question 27

How does the atomic radius affect the size of the ionisation enthalpy?

Answer 27

The further the outer shell electrons are from the positive nucleus, the less they’ll be attracted towards the nucleus. So, the ionisation enthalpy will be lower.

Question 28

How does the nuclear charge affect the size of the ionisation enthalpy?

Answer 28

This is the positive charge on the nucleus caused by the presence of protons. The more protons there are in the nucleus, the more it’ll attract the outer electrons - it’ll be harder to remove the electrons, so the ionisation enthalpy will be higher.

Question 29

How does the electron shielding affect the size of the ionisation enthalpy?

Answer 29

The inner electrons shield the outer electrons from the attractive force of the nucleus. Because more inner shells mean more shielding, the ionisation enthalpy will be lower.

Question 30

How do the first ionisation enthalpies change as you go down the group?

Answer 30

Decrease.

Question 31

Why do the first ionisation enthalpies decrease as you go down the group?

Answer 31

Because there’s less attraction between the nucleus and outer electrons.

Question 32

What does the fact that first ionisation enthalpies decrease as you go down the group because there’s less attraction between the nucleus and outer electrons tell us about how the electrons are arranged?

Answer 32

Shows that the electrons are arranged in energy levels.

Question 33

How does the attraction between the electrons and the nucleus change as you go down the group and why?

Answer 33

Electrons shells get further from the nucleus so they’re attracted to the nucleus less.

Question 34

How does the amount of electron shielding change as you go down the group and why?

Answer 34

Amount of shielding increases because there are more filled inner shells meaning there is less nuclear attraction for the outer shell electrons.

Question 35

Why doesn’t the fact that the number of protons increases down the group lead to an increase in ionisation enthalpy?

Answer 35

Because it is a less important factor than either shielding or the distance of the outer electrons from the nucleus.

Question 36

How do first ionisation enthalpies change across a period?

Answer 36

They increase.

However there are small drops between groups 2 and 3.

Question 37

Why do first ionisation enthalpies increase as you go across a period?

Answer 37

Because the number of protons is increasing, so the outer electrons are attracted more strongly to the nucleus. Also, since all the outer electrons are at roughly the same energy level, there’s generally little shielding effect or extra distance to lessen the attraction from the nucleus.

Question 38

What are the ionisation enthalpies like in s-block metals?

Answer 38

Low.

Question 39

Why do s-block metals have low first ionisation enthalpies?

Answer 39

They have relatively low nuclear charges meaning that they lose their outer electron easily, as there is less attraction between the nucleus and the outer electrons. This makes the s-block metals more reactive.

Question 40

Which have higher nuclear charges: s-block metals or p-block metals?

Answer 40

p-block metals.

Question 41

Why do p-block metals have higher nuclear charges than s-block metals?

Answer 41

Because there is an increase in the number of protons across each period meaning that they have higher first ionisation enthalpies, so it is more difficult to lose their outer electron and they are less likely to lose an electron.