trends in the periodic table

Question 1

what is the trend in atomic radius across period 3?

Answer 1

decreases

because there is more attraction between the neutrons and outer electrons

and theres no additional shielding

Question 2

define: first ionisation energy

Answer 2

the energy required to remove one mole of electrons from one mole of atoms

Question 3

explain the trend in ionisation energy across period 3

Answer 3

generally increases

because the nuclear charge increases

the electrostatic attraction between the the nucleus and outer electrons increases

and there is no additional shielding

Question 4

explain the first dip in ionisation energy across period 3

Answer 4

the first dip is between Mg and Al

Mg has a higher first ionisation energy than Al because

the outer electrons in Al are being removed from the 3p orbital

which is higher in energy

Question 5

explain the second dip in ionisation energy across period 3

Answer 5

the second dip is between P and S

P has a higher first ionisation energy than S because

S has a pair of electrons in the 3p orbital

this causes repulsion

Question 6

what period 3 elements are metals and what bonds do they form?

Answer 6

Na, Mg, Al

metallic bonds

Question 7

what period 3 oxide is a metalloid and what does it exist as?

Answer 7

Si

giant covalent lattice

Question 8

what period 3 elements are non metals and what bonds do they form?

Answer 8

P, S, Cl

covalent bonds

Question 9

why doesnt Ar react?

Answer 9

it doesnt form bonds

Question 10

describe the metallic bonding in Mg

Answer 10

made up of cations surrounded by a sea of delocalised electrons

Question 11

explain why melting point increases across period 3

Answer 11

across period 3, the metal cations have a higher charge

and therefore have more delocalised electrons

this means that there is more attraction between each cation and the delocalised electrons

Question 12

explain why Mg has a higher melting point than Na

Answer 12

Na forms Na+, Mg forms Mg2+

so Mg has more delocalised electrons

so theres more electrostatic attraction between the cations and the delocalised electrons

so the metallic bonding is stronger in magnesium than in sodium

so more energy is required to weaken Mgs bonds

so Mg has a higher melting point than Na

Question 13

what does P, S, and Cl exist as?

Answer 13

P4

S8

Cl2

Question 14

explain why silicon has a high melting point

Answer 14

silicon forms a giant covalent lattice

so it has strong covalent bonds

which need lots of energy to break

therefore it has a high melting point

Question 15

why does P have a lower melting point than S

Answer 15

P forms P4 and S forms S8

so P molecules are smaller than S molecules

so the van der waals forces between the P molecules are weaker than the van der waals forces between the S molecules

so less energy is required to break the intermolecular forces between the P molecules

so P has a lower melting point than S

Question 16

structure and melting point of:

Na2O, MgO, and Al2O3

Answer 16

ionic lattice

high melting point because

strong electrostatic force of attraction

which requires a lot of energy to break

Question 17

why does SiO2 have a high melting point?

Answer 17

exists as a giant covalent structure

so lots of energy needed to break the bonds

Question 18

why does P4O10 have a higher melting point than SO3 or SO2

Answer 18

because P4O10 has the strongest van der waals forces and therefore the highest melting point

Question 19

why does SO3 have a higher melting point than SO2

Answer 19

because it has one more oxygen atom

and therefore stronger van der waals forces

Question 20

why does the bonding in Al2O3 have some covalent character

Answer 20

aluminiums cations are smaller and

so get closer to the oxide ions

and are strongly charged enough to distort the electron cloud

Question 21

why are sodium oxide and magnesium oxide strong bases?

Answer 21

because they both dissociate into a 2- ion, which readily forms the OH- ion

Question 22

explain why SiO2 doesnt react with water

Answer 22

water cannot break apart the giant covalent lattice of SiO2

Question 23

define: amphoteric

Answer 23

reacts with both acids and bases

Al

Question 24

which oxides form ionic lattices

Answer 24

Na2O

MgO

K2O

Question 25

what holds the atoms together in a molecule of SO2

Answer 25

covalent bonds

Question 26

what bonds/forces exist between molecules of SO2

Answer 26

van der waals forces

dipole - dipole forces

Question 27

explain how the covalent character of aluminium oxide arises

Answer 27

the aluminium cation is very small

this means the aluminium cation is closer to the oxide ion

the cation is often highly charged enough to distort the electron cloud

therefore the electron cloud appears more covalent