Periodic Table

Question 1

What factors affect radius and first IE ? With explanation

Answer 1

Nuclear charge
- increases when number of protons increase

Shielding effect
- increases when number of inner electron shells increase

Effective nuclear charge
- accounts both NC and SE, if both increase ENC cancels out
- only NC increase, ENC increase

Question 2

How does atomic radius change across a period ?

Answer 2

Across a period
- NC increases as number of protons increases
- SE relatively constant as electrons are added to valence shell and there is no change in number of inner electron shells
- ENC increases leading to stronger attraction between the nucleus and valence electrons, valence electrons are pulled closer to nucleus causing atomic radius to DECREASE

Question 3

How does atomic radius change down a group ?

Answer 3

Down a group
- NC increase as number of protons increase
- SE increases as number of inner shell electrons increase
- ENC remains relatively constant
- the distance between the nucleus and valence electrons increase due to increase in number of electron shells, resulting in weaker attraction between nucleus and valence electrons, thus atomic radius INCREASES

Question 4

How does cation radius change across third period ?

Answer 4

From Na+ to Si4+
- NC increases as number of protons increase
- SE constant as cations have same number of electrons
- ENC increases leading to stronger attraction between the nucleus and valance electrons so the valence electrons are pulled closer to the nucleus causing ionic radius to DECREASE

Question 5

How does anion radius change across the third period ?

Answer 5

From P3- to Cl-
- NC increases as number of protons increase
- SE same as anions have same number of electrons
- ENC increases leading to stronger attraction between valence electrons and nucleus so valence electrons are pulled closer to nucleus casing ionic radius to DECREASE

Question 6

How is the ionic radius different for cation and anions across the third period ?

Answer 6

Anions have larger radii as there is an extra shell of electrons present

Question 7

How does ionic radius change down a group ?

Answer 7

Down a group
- NC increases as number of protons increase
- SE increases as number of inner shell electrons increase
- ENC remains constant
- the distance between the nucleus and valence electrons increases due to increase in number of electron shells resulting in weaker attraction between the nucleus and valence electrons, causing ionic radius to INCREASE

Question 8

How does first IE change across a period ?

Answer 8

Across a period
- NC increases as number of protons increase
- SE remains constant as number of inner shell electrons are the same
- ENC increases leading to stronger attraction between the nucleus and valence electrons so more energy is required to remove the valence electron, hence first IE INCREASES

Question 9

What are the deviations in first IE across third period ? With explanation

Answer 9

First IE for Aluminium is lower than Mg
- first electron to be removed from AL is from 3p subshell while first electron to be removed from Mg is 3s subshell
- electron in 3p subshell is further away from nucleus compared to 3s subshell, the 3p subshell is of higher energy level than 3s subshell and its electron is less strongly attracted to nucleus
- less energy is required to remove an electron from 3p subshell than a 3s subshell

First IE for S is lower than P
- first electron to be removed in S is a paired 3p electron compared to unpaired 3p electron for P
- easier to remove paired 3p electron in S than unpaired 3p in P due to presence of inter-electronic repulsion between electrons in the same orbital
- less energy required to remove paired 3p electron in S

Question 10

How does first IE change between periods ?

Answer 10

Huge dip in first IE after each period due to extra shell of inner electrons in atom of next period

Question 11

How does first IE change down a group ?

Answer 11

Down a group
- NC increases as number of protons increase
- SE increases as number of inner shell electrons increase
- ENC remains constant
- distance between nucleus and valence electrons increase due to increase in number of electron shells, weaker attraction between nucleus and valance electrons thus less energy required to remove valence electrons, thus first IE DECREASES

Question 12

How does reactivity of group 1 metals change down the group ?

Answer 12

(Same as first IE)
Down group
- NC increases as number of protons increase
- SE increases as number of inner shell electrons increase
- ENC remains unchanged
- distance between valence electrons and nucleus increases due to an increase in number of electron shells, resulting in weaker attraction between valence electrons and nucleus thus less energy is required to remove the valence electrons
- ease of losing electrons increases, thus reducing strength/reactivity INCREASES

Question 13

How does electronegativity change across a period ?

Answer 13

Across period
- NC increases as number of protons increase
- SE constant as number of inner shell electrons same
- ENC increases leading to stronger attraction between nucleus and electrons so the ability of the atom to attract electrons to itself increases, hence electronegativity INCREASES

Question 14

How does electronegativity change down a group ?

Answer 14

Down group
- NC increases as number of protons increase
- SE increases as number of inner shell electrons increase
- ENC constant as increase in NC and increase in SE cancel out
- increase in number of electron shells increases the distance between nucleus and valence electrons, resulting in weaker attraction between the nucleus and valence electrons, so ability of atom to attract electron to itself decreases and electronegativity DECREASES

Question 15

How does MP change across third period ?

Answer 15

Na, Mg, Al
- giant metallic structures and HIGH mp
- melting involves breaking of strong metallic bonds between the metal cation and sea of delocalised electrons which requires a large amount of energy
- metallic bonds become stronger across the period due to increasing charge density of cations and increase in number of delocalised electrons, mp INCREASES

Si
- giant molecular structure made up of Si atoms held by an extensive network of strong covalent bonds
- large amounts of energy required to break the numerous strong covalent bonds, thus Si has VERY HIGH mp

P, S, Cl, Ar
- non-metals with simple molecular structure
- molecules are held by weak id-id interaction, only a small amount of energy required to overcome the weak id-id interactions thus LOW mp
- S has greatest number of electrons, electron cloud is the most polarisable thus id-id between S8 molecules are the strongest thus require greatest amount of energy to overcome
- mp DECREASES across period as number of electrons decreases and electron cloud becomes less polarisable

Question 16

How does electrical conductivity change across third period ?

Answer 16

Na, Mg, Al
- metals with delocalised sea of electrons which can act as mobile charge carriers hence have HIGH electrical conductivity
- number of delocalised electrons increase across the period hence electrical conductivity INCREASES

Si
- semi-metal which behaves as a semiconductor hence has LOW conductivity between conductor and insulator

P, S, Cl, Ar
- non-metals with simple molecular structure
- do not have mobile charge carriers and are hence electrical insulators

Question 17

How does bonding of third period oxides change across the period ?

Answer 17

Changes from ionic to covalent
- from Na to Al, charge density increases leading to increase in polarising power, the electron cloud of oxide experience increased distortion thus covalent character increases

Question 18

How does MP change across oxides of third period ?

Answer 18

Na2O, MgO, Al2O3,
- giant ionic structures, HIGH mp
- a lot of energy is needed to overcome the strong ionic bonds during melting
- Mg2+ has higher charge and smaller radius than Na+, more exo LE thus stronger ionic bonds
- Al2O3 has lower mp due to mix of covalent and ionic character

SiO2
- giant molecular structure, HIGH mp (lower than Al)
- extensive network of strong covalent bonds between Si and O, a lot of energy is required to break the strong covalent bonds

P4O10, SO3, Cl2O
- simple molecular structures, LOW mp
- both P4O10 and SO3 are non-polar, small amount of energy needed to overcome id-id interaction between the molecules, mp DECREASES as number of electrons decrease which leads to weaker id-id

Question 19

Structure and nature of Na2O
Reaction with water
pH

Answer 19

Giant ionic structure, basic oxide

Dissolves in water : Na2O (s) + H2O (l) —> 2 NaOH (aq)

pH = 13

Question 20

Structure and nature of MgO
Reaction with water
pH

Answer 20

Giant ionic, basic oxide

Highly exo lattice energy, hard to dissolve in water, reaction is reversible :
MgO (s) + H2O (l) <==> Mg(OH)2 (aq)

pH = 9

Question 21

Structure and nature of Al2O3
Reaction with water
pH

Answer 21

Giant ionic, amphoteric oxide

Highly exo lattice energy, strong ionic bonds with covalent characters thus insoluble in water

pH = 7

Question 22

Structure and nature of SiO2
Reaction with water
pH

Answer 22

Giant molecular, acidic oxide

Held by numerous stronger covalent bonds making it insoluble in water

pH =7

Question 23

Structure and nature of P4O10
Reaction with water
pH

Answer 23

Simple molecular, acidic oxide

Readily dissolves in water : P4O10 (s) + 6 H2O (l) —> 4 H3PO4 (aq)

pH = 2

Question 24

Structure and nature of SO3
Reaction with water
pH

Answer 24

Simple molecular, acidic oxide

Reacts violently with water : SO3(g) + H2O (l) —> H2SO4 (aq)

pH = 2

Question 25

Reaction with acid / base of Na2O

Answer 25

Acid :
Na2O(s) + 2HCl(aq) → 2NaCl(aq) + H2O(l)

Base :
No reaction

Question 26

Reaction with acid / base of MgO

Answer 26

Acid :
MgO(s) + 2HCl(aq) → MgCl2(aq) + H2O(l)

Base :
No reaction

Question 27

Reaction with acid / base of Al2O3

Answer 27

Acid :
Al2O3(s) + 6HCl(aq) → 2AlCl3(aq) + 3H2O(l)

Base :
Al2O3(s) + 2NaOH(aq) + 3H2O(l) → 2NaAl(OH)4(aq)

Question 28

Reaction with acid / base of SiO2

Answer 28

Acid :
No reaction

Base :
SiO2(s) + 2NaOH(conc.) → Na2SiO3(aq) + H2O(l)

Question 29

Reaction with acid / base of P4O10

Answer 29

Acid :
No reaction

Base :
P4O10(s) + 12NaOH(aq) → 4Na3PO4(aq) + 6H2O(l)

Question 30

Reaction of acid / base with SO3

Answer 30

Acid :
No reaction

Base :
SO3(g) + 2NaOH(aq) → Na2SO4(aq) + H2O(l)

Question 31

Trend of reactivity of chlorides across third period

Answer 31

Forms increasingly acidic solutions and undergo hydrolysis more readily
- change from ionic to covalent

Question 32

Bond of NaCl
Reaction with water
pH

Answer 32

Ionic

Dissolves without hydrolysis : NaCl (s) —> Na+ (aq) + Cl- (aq)

pH = 7

Question 33

Bond of MgCl2
Reaction with water
pH

Answer 33

Ionic with some covalent character

Dissolve with slight hydrolysis
- dissolve : MgCl2 (s) + 6 H20 (l) —> [Mg(H2O)6]2+ (aq) + 2Cl- (aq)
- hydrolysis : [Mg(H2O)6]2+ (aq) + H2O (l) <==> [Mg(H2O)5(OH)]+ (aq) + H3O+ (aq)

pH = 6.5

Question 34

Bond of AlCl3
Reaction with water
pH

Answer 34

Ionic with covalent character

Dissolves with appreciable hydrolysis
- dissolve : AlCl3(s) + 6H2O (l) —> [Al(H2O)6]3+ (aq) + 3Cl- (aq)
- hydrolysis : [Al(H2O)6]3+ (aq) + H2O (l) <==>