3.2.1 - PERIODICITY

Question 1

Describe and explain the trend of melting points from Na to Al (period 3)

Answer 1

• increases
• charge of the metal cation increases
• attraction between cation and delocalised electrons increase, requiring more energy to break

Question 2

Describe and explain the change in melting point from Aluminium to Silicon (period 3)

Answer 2

• increases
• Si is a giant covalent macromolecule
• infinite lattices, where atoms are held together by strong covalent bonds
• these require large amounts of energy to break

Question 3

Describe and explain how melting points change from phosphorus to argon

Answer 3

• they are simple molecular structures
• change depending on how large the molecule is
• the larger the molecule, the more electrons
• the greater the magnitude of temporary and induced dipoles, increasing the strength of VdW’s

Question 4

State the molecular formula for Phosphorus

Answer 4

P4

Question 5

State the molecular formula for sulfur

Answer 5

S8

Question 6

State the molecular formula for chorine

Answer 6

Cl2

Question 7

State the molecular formula for argon

Answer 7

Ar

Question 8

Describe and explain what happens to atomic radius across a period

Answer 8

• decreases
• nuclear charge increases
• shielding stays the same
• attraction between nucleus and electrons increases, pulling the atom closer together

Question 10

Which element in period 3 has the highest melting point and why

Answer 10

• silicon, Si
• it is macromolecular
• atoms bonded together with strong covalent bonds
• require lots of energy to overcome

Question 11

Which period 3 oxide is insoluble in water and why

Answer 11

• Al2O3 (aluminium oxide)
• close packing structure

Question 12

• which period 3 hydroxide is used in medicines
• how/why

Answer 12

• Mg(OH)2
• used in milk of magnesia
• slightly soluble, so can raise pH of stomach acid slightly

Question 13

• describe and explain the general trend in ionisation energy for period 3
• state which elements deviate from this

Answer 13

• generally increases, more energy required to remove outer electron
• nuclear charge increases
• atomic radius decreases
• Al and S deviate from the trend

Question 14

Why does Aluminium deviate from the ionisation energy trend along period 3

Answer 14

• has 13 electrons
• outermost electron in 3p sub shell
• higher in energy, so is easier to remove the electron
• requires less energy

Question 15

Why does Sulfur deviate from the trend in ionisation energy along period 3?

Answer 15

• has 16 electrons
• electrons in the 3p sub shell are paired in an orbital
• experience more repulsion, easier to remove
• requires less energy to remove electron

Question 16

• What does it mean if ionisation energy for an element greatly increases after a specific number?
• E.g. jump in ionisation energy after the 5th electron is removed

Answer 16

• means that the next electron (e.g. the 6th) is being removed from the 2nd energy level, closer to the nucleus
• suggests that there is 5 electrons in its outer shell
• so is a group 5 element