The Periodic table trends

Question 1

What do elements in a period show?

Answer 1

A trend in physical and chemical properties

Question 2

Why do elements in a period show a trend in physical and chemical properties?

Answer 2

They have different electron configurations

Question 3

What is a group?

Answer 3

A vertical column in the periodic table

Question 4

What is a period?

Answer 4

A horizontal row in the periodic table

Question 5

Do elements in the same group have the same or different number of electrons in their outer shell?

Answer 5

Same

Question 6

Do elements in the same group have the same or different types of orbital in the outer shell

Answer 6

Same

Question 7

Do elements in the same group have outer electrons in the same or different quantum shell?

Answer 7

Different

Question 8

How is the periodic table arranged?

Answer 8

In order of increasing atomic number

Question 9

Do elements in the same period have the same or different numbers of electrons in their outershells?

Answer 9

Different

Question 10

Do elements in the same period have the same or different types of orbitals in their outer shells?

Answer 10

Different

Question 11

Define periodicity

Answer 11

A repeating trend in properties of the elements across each period of the periodic table

Question 12

What do elements in the same group show?

Answer 12

Similar physical and chemical properties

Question 13

Why do elements in the same group have similar chemical and physical properties?

Answer 13

They have a similar electronic configuration

Question 14

Define 1st ionisation energy

Answer 14

The amount of energy required to remove one electron from EACH ATOM in one mole of gaseous atoms to form one mole of gaseous 1+ ions

Question 15

What is the general trend in 1st ionisation energy across a period?

Answer 15

It increases

Question 16

What is the general trend in 1st ionisation energy down a group?

Answer 16

It decreases

Question 17

What is the trend observed between group 0 1st of one period and the group 1 element of the next period?

Answer 17

There is a sharp drop

Question 18

Why is there a sharp drop in 1st IE observed between group 0 of one period and group 1 element of the next?

Answer 18

• electrons are being removed from a new electron shell
• this shell is further from the nucleus and experiences more shielding despite the increase in nuclear charge
• the overall nuclear attraction is weaker
• therefore less energy is required to remove the outer electron

Question 19

What 4 factors affect the value of ionisation energy?

Answer 19

• number of electron shells
• atomic radius
• number of protons
• nuclear attraction

Question 20

Explain the general trend in 1st ionisation energy across a period

Answer 20

• 1st ionisation energy increases
• nuclear charge increases across a period
• shielding does not change across a period
• atomic radius gets smaller across a period
• therefore attraction between the nucleus and outer electron becomes greater

Question 21

Explain the general trend in 1st ionisation energy down a group

Answer 21

• 1st IE decreases down a group
• shielding increases down a group
• atomic radius increases down the group
• although nuclear charge increases, the other factors outweigh this
• there is a decrease in nuclear attraction

Question 22

Some points do not obey the general trend in 1st ionisation energy- where are these?

Answer 22

• between groups 2 and 3

- between groups 5 and 6

Question 23

Explain the difference in 1st ionisation energy between Be and B

Answer 23

• the fall in IE marks the start of filling the p subshell
• in Be the outer electron is in a 2s orbital
• in B the outer electrons is in a 2p orbital
• the 2p orbital in B is of higher energy and experiences more shielding from inner electrons as it is also shielded by the electrons in the 2s subshell
• despite the fact the nuclear charge increasing by +1 from Be to B the difference in shielding and energy means the nuclear attraction is weaker in B
• less energy required to remove the electron

Question 24

Explain difference in 1st ionisation energy between N and O

Answer 24

• the fall in IE between groups 5 and 6 marks the start of electron pairing in the p-orbitals in p-subshell
• In N the outer electron is unpaired in a 2p orbital
• In O the outer electron is paired in a 2p orbital
• The paired electrons in O repel slightly
• This makes it easier to remove an electron from O than N

Question 25

What is the trend in melting points across periods 2 and 3?

Answer 25

- Groups 5-8 have much lower melting points - Group 4 elements occupy the peaks of melting points - melting points increase from group 1 to group 2 to group 3

Question 26

Why do group 4 elements occupy the peaks of melting points?

Answer 26

- Carbon and Silicon have giant covalent structures - each atom makes 4 covalent bonds - all of these bonds must be broken which requires a lot of energy - whereas Boron only makes 3 covalent bonds

Question 27

Why do elements with diatomic molecules or single atoms have the lowest melting points?

Answer 27

- simple covalent structure - only intermolecular forces must be overcome, no bonds - the strength of London forces is related to the no. electrons that can take part in instantaneous induced dipole-induced dipole interactions - smaller the molecule the smaller the London forces the lower melting point

Question 28

Why do melting points increase from group 1 to group 2 to group 3?

Answer 28

- metallic bonding present - metallic bonding increases as the number of electrons present that can be delocalised increases and as nuclear charge increases - The charge on the metal ion increases from group 1 (1+) to group 2 (2+) to group 3 (3+) - therefore there are more delocalised electrons in the structure - therefore the strength of electrostatic attraction between positive ions and delocalised electrons increases along the group - More energy is needed to overcome these attractions

Question 29

What is the trend in electrical conductivity across period 3?

Answer 29

Electrical conductivity increases from sodium to magnesium to aluminium

Question 30

Why does electrical conductivity increase from sodium to magnesium to aluminium?

Answer 30

- the charge on ions increases - so the number of delocalised electrons within the metallic bond increases - delocalised electrons act as mobile charge carriers so conduct electricty - more delocalised electrons means greater electrical conductivity

Question 31

Why do elements with molecular structures have poor electrical conductivity?

Answer 31

-because they do not contain any mobile charge carriers

Question 32

What is the trend in atomic radius across periods?

Answer 32

-atomic radius decreases

Question 33

Why does atomic radius decrease across periods?

Answer 33

- across a period there is little change in shielding - there is a regular increase in nuclear charge - the nuclear attraction increases - electrons are pulled more strongly towards the nucleus

Question 34

What the trend in atomic radius down the group?

Answer 34

It increases

Question 35

Why does atomic radius increase down the group?

Answer 35

- there are increasing numbers of electron shells - therefore shielding increases - the attraction of electrons by the nucleus is less