Unit 2: Section 1- Periodicity

Question 1

Define periodicity

Answer 1

Periodicity is the study of patterns in the chemical or physical properties of elements going across the periods of the periodic table

Question 2

What are the four blocks that the periodic table is divided up into?

Answer 2

s, p, d and f

Question 3

What does the block that an element is in depend upon?

Answer 3

It depends on the orbital in which the outermost electron, the valence electron, of the element is found.

Question 4

What block are Group 1 and 2 elements found in?

Answer 4

s

Question 5

What block are Group 3 elements found in?

Answer 5

p

Question 6

What elements are found in block d?

Answer 6

the transition metals

Question 7

Where can the f block be found?

Answer 7

below the periodic table

Question 8

What is the trend between atomic radius and moving left to right across a period?

Answer 8

As you go from left to right across a period, the atomic radius decreases

Question 9

Explain why the atomic radius decreases going from left to right across a period

Answer 9

As we go across a period the number of protons found in the elements nucleus increases. This increases the nuclear charge of the elements, thereby creating a stronger electrostatic attraction between the nucleus and the electrons of the element
The same amount of shielding is present across the period, so the nucleus of an element is able to pull its valence electrons closer to itself

Question 10

What is shielding?

Answer 10

It is the electrostatic repulsion felt between negatively charged electrons and how much this cancels out the attraction of electrons to the nucleus

Question 11

What is the trend in shielding across a period and why?

Answer 11

It stays roughly the same, because the outer electron from each element in a period is found in the same shell

Question 12

Define first ionisation energy

Answer 12

enthalpy change when one mole of gaseous atoms forms one mole gaseous ions (1+ charge)

Question 13

What happens to first ionisation energy moving across a period?

Answer 13

It increases, so more energy is needed to remove the valence electron from the element to form an ion

Question 14

Explain why first ionisation energy increases along a period

Answer 14

Increasing nuclear charge and attraction leads to an increase in first ionisation energy
As shielding remains similar, there is no significant increase in repulsion of this outer electron and so ionisation energy increases

Question 15

Name four exceptions to the trend of increasing first ionisation energy

Answer 15

Magnesium and Aluminium
Phosphorus and Sulfur

Question 16

What happens to the trend in first ionisation energy between magnesium and aluminium?

Answer 16

Between magnesium and aluminium, there is a drop in the 1st ionisation energy.

Question 17

Why is there a drop in first ionisation energy between magnesium and aluminium?

Answer 17

• the outer electron of Mg is in the 3s subshell while the outer electron of Al is in the 3p subshell.
• so, when removing an electron from the Al outer shell, the electron is being removed from a 3p subshell which has a higher energy than the 3s subshell
• the higher energy level makes it easier for an electron to be removed, decreasing the energy required to remove the electron

Question 18

What happens to the trend in first ionisation energy between phosphorous and sulfur?

Answer 18

Between phosphorous and sulfur, there is a drop in the 1st ionisation energy.

Question 19

Why is there a drop in first ionisation energy between phosphorous and sulfur?

Answer 19

• the outer electron of sulfur is paired up, however the outer electron of phosphorous is not, even though they are both in the 3p orbital
• this causes a small repulsion between the two electrons (S) making it easier for an electron to be removed
• It is also more energetically favourable for the atom to have an exactly half full subshell. Sulfur can lose its outer electron to gain an exactly half filled subshell.

Question 20

What are the trends for first ionisation energy in period 3?

Answer 20

The trends for Period 3 are the exact same for Period 2. Except that the drops are between berylium and boron and nitrogen and oxygen. In an explanation, make sure to change 3p/3s orbitals to 2p/2s.

Question 21

What is the trend in MP and BP in elements across a period?

Answer 21

There is no general trend in the melting and boiling points of elements across a period. Instead a number of factors determine the individual temperatures at which each elements will melt and boil.

Question 22

What happens to the MP/BP betwen Na to Al?

Answer 22

MP/BP increases

Question 23

Why does MP/BP increase between Na and Al?

Answer 23

• There is an increase in the strength of metallic bonding.
• The metallic bonds become stronger because the number of delocalised electrons increases across the period while the ions become smaller with a greater positive charge.
• To break these bonds, a high energy is required.

Question 24

What type of MP/BP does Si have?

Answer 24

very high

Question 25

Why does Si have a very high MP/BP?

Answer 25

Silicon exists a macromolecule and therefore has lots of strong covalent bonds within it. A lot of energy is required to break these bonds so it has a very high melting and boiling point.

Question 26

Why do Cl, S and P all have low MP/BPs?

Answer 26

They are all simple molecules that contain weak Van der Waals forces. Therefore, not a lot of energy is needed to break the bonds so they have low boiling and melting points.

Question 27

What type of MP/BP do Cl, S, and P all have?

Answer 27

Low

Question 28

Why does the MP/BP slightly increase between phosphorous and sulfur?

Answer 28

Because the sulfur molecule (S8)
has more electrons than the phosphorus molecule (P4) , so it has stronger Van der Waals forces.

Question 29

What happens to the MP/BP between P and S?

Answer 29

it slightly increases

Question 30

What type of MP/BP does Ar have?

Answer 30

low

Question 31

Why does Ar have a low MP/BP?

Answer 31

It is a monoatomic element and therefor has weak Van der Waals forces and so a low MP/BP

Question 32

What is the trend in MP/BP in period 3?

Answer 32

The trends in Period 3 are similar in Period 2, except that while lithium and beryllium Be are both metals, boron is not a metal and is in fact a macromolecule so will have a very high melting point compared to the metals.

Question 33

How can you easily find the electronic structure of an element using the periodic table?

Answer 33

Label each block of the periodic table, with the groups and 1s, 2s, 2p, 3s, 3p… etc
Then read off electron configuration
Each period has a higher energy level