Physical: Shapes of molecules + Forces Arised

Question 1

explain e- pair repulsion theory

Answer 1

electrons are -vely charged so e- will repel each other, in a molecule a bonding pair of e- will repel other e- around the central atom causing a shape and bond angle and pairs will take up as much space and be as far away as possible

Question 2

give the angle for linear

Answer 2

180

Question 3

give the angle for triganol planar

Answer 3

120

Question 4

give the angle for v shaped

Answer 4

104.5
contains two lone pairs

Question 5

give the angle for pyramidal

Answer 5

107
contains a lone pair

Question 6

give the angle for tetrahedral

Answer 6

109.5

Question 7

give the trigonal bi pyramid

Answer 7

120 + 90

Question 8

give the angle for octahedral

Answer 8

90

Question 9

explain the process in calculating the bond angle of a molecule
-use trimethylamine

Answer 9

amine= nitrogen = group 5 so 5 valence e-
tri= 3 carbons= 3 bond pairs
5+3= 8
8/2= 4
4-3= 1 lone pair = pyramidal 107.

Question 10

what is the most electronegative element in the periodic table

Answer 10

Fluorine= 4.0

Question 11

explain trend in e-vity down a group

Answer 11

it decreases due to increase in atomic radii and and shielding so further away the outer most e- so less attractions between nucleus and e- so less able to attract pairs of electrons

Question 12

explain trend in e-vity across a period

Answer 12

it increases as shielding stats about the same but atomic radii decreases due to increase in nuclear charge/ proton number so a stronger attraction between nucleus and outer most electron

Question 13

what is difference between Intramolecular force and intermolecular forces

Answer 13

Intramolecular forces are forces within a molecule, whereas intermolecular forces are forces between a molecule.
Molecules contain weaker intermolecular force between the molecules:

Induced dipole – dipole forces also called van der Waals or London dispersion forces
Permanent dipole – dipole forces are the attractive forces between two neighbouring molecules with a permanent dipole
Hydrogen Bonding are a special type of permanent dipole - permanent dipole forces
Intramolecular forces are stronger than intermolecular forces
For example, a hydrogen bond is about one tenth the strength of a covalent bond

Question 14

give the order of strength between forces that arise within molecules

Answer 14

covalent
hydrogen
permanent dipole-dipole
induces dipole- dipole (VdW)

Question 15

what is non polar

Answer 15

When two atoms in a covalent bond have the same electronegativity the covalent bond is nonpolar

Question 16

explain how polarity occurs

Answer 16

two atoms in a covalent bond have different electronegativities the covalent bond is polar and the electrons will be drawn towards the more electronegative atom
As a result of this:
The negative charge centre and positive charge centre do not coincide with each other
This means that the electron distribution is asymmetric
The less electronegative atom gets a partial charge of δ+ (delta positive)
The more electronegative atom gets a partial charge of δ- (delta negative)

Question 17

explain how permanent dipole- dipole come about

Answer 17

polar molecules have permanent dipoles and the molecule will always have +ve and -ve ends, so with its neighbouring molecule will be attracted that already are polar

Question 18

explain how induced dipole dipole occur

Answer 18

induced dipole - dipole forces exist between all atoms or molecules
They are also known as van der Waals forces
electron charge randomly shifts (since constantly moving) causing one end to be more -ve, forming temporary dipole, this induces neighbouring molecules

Question 19

explain hydrogen bonding

Answer 19

it is the strongest type of bond between molecules only contains N,O,F since very electronegativity ,hydrogen is covalently bonded to an O, N or F, the bond becomes highly polarised
(bonds only to lone pairs) dotted lines must be shown

Question 20

explain the trend in bp between hydrogen bonding and group 6 elements

Answer 20

H2O highest enthalpy due to h bonding which requires most energy to overcome but this is not present in other hydrides
H2S is immediately lower and increases H2Se and H2Te due to the number of electron number increases
this increases the number of van der walls forces/ induces d-d forces as the molecule becomes larger