chem bonding

Question 1

what is electronegativity?

Answer 1

the measure of an atom’s ability to attract electrons in a covalent bonds to itself

Question 2

what is the trend of electronegativity down a group? explain.

Answer 2

down a group, electronegativity decreases - effective charge increase, shielding effect increase, no. of quantum shells increase, hence outermost electrons are further away from nucleus so nucleus of the atom has a weaker attraction for electrons of another nucleus

Question 3

what is the trend of electronegativity across the period?explain.

Answer 3

across a period, electronegativity increases - effective nuclear charge increase, shielding effect remains unchanged, hence nucleus of atom has higher attraction for electrons of another nucleus

Question 4

what is a covalent bond?

Answer 4

the electrostatic force of attraction between the positively charged nucleus of both atoms and their shared electrons

Question 5

what are the factors affecting the strength of a covalent bond?

Answer 5

1. bond length - bond length increase, covalent bond strength decrease
2. bond order - no. of covalent bonds between a pair of atoms - bond order increase, bond strength increase

Question 6

what is a sigma bond and a pi bond?

Answer 6

head on overlap and side on overlap. a sigma bond must exist first for a pi bond to exist

Question 7

what is a metallic bond?

Answer 7

the electrostatic force of attraction between a lattice of metal cations and sea of delocalised valence electrons

Question 8

what are the factors affecting the strength of a metallic bond?

Answer 8

1. charge and radius of cation - charge increase, radius decrease, charge density increase, hence strength increase
2. no. of valence electrons contributed per atom - ~ increase, no. of delocalised electrons increase, hence strength increase

Question 9

what are alloys? what are the properties of alloys?

Answer 9

they are mixtures of metals (with small quantities of other elements). they make metals harder as the atoms of different sizes disrupt the orderly arrangement of the main metal atoms so they cannot slide over each other easily when force is applied.

Question 10

what is an ionic bond?

Answer 10

it is the electrostatic force of attraction between oppositely charged ions in a giant ionic lattice

Question 11

what are the factors affecting the strength of ionic bonding?

Answer 11

1. ionic charge (greater impact)

2. ionic radius

Question 12

what is lattice energy?

Answer 12

the heat evolved when 1 mole of pure ionic solid is formed from its constituent gaseous ions

Question 13

what are the types of intermolecular forces of attraction?

Answer 13

1. dispersion forces/ instantaneous dipole-induced dipole attraction
2. permanent dipole-permanent dipole attraction
3. hydrogen bonding

Question 14

when do dispersion forces occur?

Answer 14

non polar molecules/atoms

Question 15

what are the factors affecting the strength of dispersion forces?

Answer 15

1. no. of electrons - ~increase, size of electron cloud increase, polarisability increase, dispersion forces form more easily, hence strength increase
2. surface area of of contact - ~increase, s.a for electron cloud to be distorted increase (for molecules with a similar no. of electrons)

Question 16

what are the factors affecting the strength of pd-pd attractions?

Answer 16

net dipole moment - ~increase, strength increase

Question 17

when do pd-pd attractions occur?

Answer 17

polar molecules

Question 18

what are the conditions for hydrogen bonding to occur?

Answer 18

1. one molecule must contain a hydrogen atom bonded to F, O or N
2. the other molecule must have F, O or N with lone pair of electrons

Question 19

what is a giant molecular compound

Answer 19

a network of covalent solids which do not consist of discrete molecules. the atoms are held together by covalent bonds in a giant covalent lattice structure

Question 20

what is the structure of diamond?

Answer 20

each c atom is covalently bonded to 4 other c atoms and form a tetrahedral structure

Question 21

what are the properties of diamond?

Answer 21

hard, high mp/bp/insoluble in any solvent

Question 22

what is the structure of graphite?

Answer 22

each c atom is covalently bonded to 3 other c atoms

Question 23

what is the structure of quartz/sand?

Answer 23

each si atom is covalently bonded to 4 other o atoms and each o atom is covalently bonded to 2 other si atoms

Question 24

what makes an ionic compound soluble in water?

Answer 24

ion-dipole interactions - occurs between an ion and the oppositely charged end of a dipole, is weaker than ionic bonding but stronger than hydrogen bonding, pd-pd and dispersion forces

Question 25

how do you explain the solubility/ miscibility of a substance in a given solvent?

Answer 25

1. identify type of interaction holding solute particles together and solvent particles together
2. identify type of interaction that can occur between solute and solvent particles
3. compare relative strength
4. since the energy released from solute-solvent interactions is greater than or comparable to the energy required to overcome solute-solute interactions and solvent-solvent interactions, X is soluble/ miscible in Y

Question 26

what is dative bonding?

Answer 26

when one of the atoms provides both bonding electrons

Question 27

what are the conditions for a dative bond to form?

Answer 27

1. donor atom must have a lone pair of electrons

2. acceptor atom must contain an empty orbital in its valence shell

Question 28

what is an electron deficient species?

Answer 28

an atom/molecule that requires fewer than the number of electrons required for maximum stability

Question 29

why does expansion of octet occur?

Answer 29

elements from period 3 onwards can utilise their d orbitals in covalent bonding as d orbitals are energetically accessible

Question 30

why are some elements unable to undergo expansion of octet?

Answer 30

their 3d orbitals are not energetically accessible as 3d orbitals are in a different outer quantum shell, which is at a much higher energy level than its valence shell