Periodicity

Question 1

Define periodicity?

Answer 1

Repeating pattern of physical or chemical properties going across periods

Question 2

Trend in atomic radii across a period

Answer 2

Decreases –> increased number of protons in nucleus creates a more positive attraction for electrons in the same shell with similar shielding

Question 3

General trend in first ionisation energy in period 3

Answer 3

Increases –> increased number of protons as electrons are added to the same shell

Question 4

Explain the trend between Mg and Al for first ionisation energy

Answer 4

Small drop

–> Mg has all outer electrons in the 3s sub shell but Al begins too fill the 3p sub shell

–> 3p electrons are higher in energy so they’re slightly easier to remove

Question 5

Explain the trend between P and S in first ionisation energy

Answer 5

Small drop

–> Sulfur’s outer electrons are being paired up with another electron from the same 3p orbital

–> Causes slight repulsion between 2 negatively charged electrons

–> Making the second one easier to remove

Question 6

General trend in 1st ionisation energy in period 2

Answer 6

General increase due to increased protons as electrons are added to the same shell

Question 7

Trend between Be and B for first ionisation energy

Answer 7

Small drop

–> All outer electrons in Be are in 2s sub shell but B begins to to fill the 2p subshell

–> 2p electrons are higher in energy so they’re slightly easier to remove

Question 8

Trend between N and O

Answer 8

Small drop

–> Electrons in 2p sub shell begin to pair up with another electron in the same orbital

–> Causing slight repulsion between 2 negatively charged electrons

–> So second one is easier to remove

Question 9

Trend in melting / boiling points of Na, Mg, Al

Answer 9

Metallic bonding

1) Bonds get stronger as more electrons in the outer shell are released

2) Smaller ion with greater positive charge makes bonding stronger too –> due to strong electrostatic forces of attraction between positive metal ions and delocalised electrons

3) High energy needed to break bonds

Question 10

Trend in melting / boiling point of Si

Answer 10

Macromolecular

1) many strong covalent bonds between atoms

2) Very high energy needed to break bonds

Question 11

Trend in melting / boiling point of Cl2, S8, P4

Answer 11

Simple molecular

1) Weak van der Waals between molecules

2) Little energy needed to break bonds

Question 12

Which has a higher melting point: S8 or P4?
Why?

Answer 12

S8

1) More electrons
2) So stronger van der Waals between molecules