2.2 covalent model part 2

Question 1

what does bond polarity arise from

Answer 1

difference in electronegativity of the bonded atoms

Question 2

what does molecular polarity depend on

Answer 2

bond polarity and molecular geometry

Question 3

electronegativity

Answer 3

relative measure of how an atom attracts a pair of electrons in a covalent bond

Question 4

what happens to pair of electron if electronegativity of both atoms is the same

Answer 4

the electron pair is equally attracted to their positive nucleii, bond will be symetrical, even distribution of negative charge

Question 5

what happens to pair of electrons if electronegativity of atoms is not equal

Answer 5

pair of electrons is more strongly attracted to more electronegative atom, bond is polar, meaning there is an unequal distribution of charge between two atoms, there is a partial negative charge on more elctronegative atom, and partial positive to the less electronegative atom

Question 6

the degree of polarisation depends on

Answer 6

the difference in electronegativity between the two atoms in the covalent bond

Question 7

describe trend in electronegativity

Answer 7

increases up periodic table and increases from left to right

Question 8

explain trend in distance of elements and polarity

Answer 8

next to each other probably not polar, seperation of 1 element then bond is polar, seperation of 2 or 3 elements then bond will be strong polar, seperation of 4 likely not covalent bond

Question 9

differnece in electronegativity greater than 0 but less than 1.8

Answer 9

polar bond

Question 10

difference in electronegativity bigger than 1.8

Answer 10

ionic bond

Question 11

why is it that even if molecule has polar bonds the molecule as a whole might not be polar

Answer 11

for molecule to be polar its shape must be such that the centres of positive and negative cannot by symmetrical arranged, if charges are symmetrical over whole molecule they can cancel each other out, resulting in the molecule itself being non-polar.

Question 12

a molecule with distinct aysemetrical regions of positive and negative charge are said to have

Answer 12

a dipole

Question 13

how is a molecular dipole shown

Answer 13

using an arrow poiting towards the region of negative charge

Question 14

intramolecular force

Answer 14

forces resulting from strong bonds within the molecule or structure, both giant and simple covalent molecular have these
to break these bonds often recquire high energy input

Question 15

intermolecular forces

Answer 15

the force of attraction between neighbouring molecules or atoms are weak

Question 16

what are the 3 main typs of intermolecular forces of attraction

Answer 16

london dispersion forces
dipole dipole forces
hydrogen bonding

from wekest->strongest

Question 17

london dispersion forces

Answer 17

present in all atoms or molecules that have electrons
the movement of electrons in the orbitals of atoms or molecules gives rise to temporary dipole, when this is formed it can induce the formation of a dipole in neighbouring atoms or molecules electrostatic attraction between the temporary and induced dipoles results in a weak attractive force to arise= london force

Question 18

van derwaals forc

Answer 18

combnation of both london and dipole dipole forces

Question 19

steps for formation of london forces

Answer 19

1. in an atom or molecule movement of electrons results in the formation of a spontaneous temporary dipole
   2.close proximity to another moelcule induces a dipole to form in the other molecule the elctron cloud becomes distorted and the molecule is polarized
   3.temporary and induced dipoles attract each other forming a weak temporaray london force

Question 20

what are the factors which influence formation of london forces

Answer 20

happens more frequently in lower temperatures as atoms or molecules move more slowly increasing frequency of force formation

Question 21

what happens in non polar molecules in terms of intermolecular forces

Answer 21

in non polar molecules london forces may be the only attractive force between molecules. Since the force is the weakest of the intermoleculcular forces, non polar molecules are often gases or liquids and slids with relitevly low melting points

Question 22

what 3 factors affect the strength of london forces

Answer 22

1.increasing number of electrons
2.increasing the volume of the electron cloud
3.increasing the contact area between molecules

Question 23

explain why increasing number of electrons icnreases strnegth of london forces

Answer 23

the greater the molar mass the bigger the number of electrons and the weaker will be the attraction for the electrons for the nucleus and the ease with which the electron cloud can be polarized (induced dipole)

Question 24

explain why increasing volume of the electron cloud increases strength of london forces

Answer 24

the greater the volume of the electron cloud the weaker will be the attraction of an electron for the nucleus and the ease with which the electron cloud can be polarised (induced dipole)

Question 25

explain why increasing contact area between molecules icnreases the strength of london forces

Answer 25

london forces is only effective over short range since the molecules or atoms need to be in close enough proximity for the temporary dipole to induce a dipole in neighbouring molecules or atoms. The means that the greater the contact area of the molecules that can come close together the greater the london force

Question 26

why do noble gases have really low melting points

Answer 26

weak london dispersion forces the only have london forces only need weak eneergy to break bon, no intramolecular polar bond

Question 27

explain the trend in melting point down the group of nobel gases

Answer 27

bigger the number of electrons bigger molar mass down the group, easier distortion to produce induced dipoles hence strength of london forces increases, increasing melting point

Question 28

explain why the melting points of halogens is higher than the noble gas in same period

Answer 28

they are diatomic, meaning double the molar mass, increased strength london force, increased surface area between separate molecules more electrons easier to distort

Question 29

explain trend in melting point down the halogen group

Answer 29

increases in m.p down the group due to increase in mass and number of electron and volume of electron cloud, hence strength of london forces increases

Question 30

explain the dipole dipole force

Answer 30

must be polar molecule this occurs because of the electrostatic attraction between moecules with a permanent dipole because this is an attraction between permenant dipoles the force is much stronger than london forces so the m.p of such susbtances with a mass similar to molecules with only london forces is higher all molecules which have dipole- dpiole forces also have london forces

Question 31

explain hydrogen Bonding

Answer 31

this occurs in molecules than contai hydrogen covalently bonded to nitrogen, oxygen or fluorine. All these three elements have non-bonding lone pairs of electrons that can interact with a hydrogen that has a permenant dipole, partial positive chagre. In addition all 3 elements are small and so are able to interact closely with the hydrogen atom.

Question 32

what is meant by sigma bond

Answer 32

overlap of atomic orbitals along the internuclear axis atomic orbitals overlap head to head

Question 33

what is a pi orbital

Answer 33

when atomic orbitals overlap sideways p-p