Shapes of Molecules

Question 1

molecules with bonded pair shapes

Answer 1

2 bonded - linear 180
3 bonded - trigonal planar - 120
4 bonded - tetrahedral 109.5 
5 bonded - trigonal bipyramidal -90,120
6 bonded - octahedral - 90

Question 2

molecules with bonded and lone pairs shapes

Answer 2

4 bonded no lone - tetrahedral - 109.5
3 bonded 1 lone - pyramidal - 107
2 bonded 2 lone - non linear - 104.5

Question 3

how many bonds counted for a bond with more thsn two electrons (forming a double bond)

Answer 3

each double bond counts as one bonded pair of electrons even if more so CO2 would be linear even though 4 electrons in each overlap

Question 4

what causes decrease in bond angle

Answer 4

lone pair of electrons repel more than bonded pairs of electrons
electron pairs repel to maximum repulsion

Question 5

electronegativity

Answer 5

measure of attraction of an atom in a molecule for the pair of electrons in a covalent bond

Question 6

effect of electronegativity on covalent compounds

Answer 6

if electronegativity difference is large, one bonded atom will have a much greater attraction for shared pair of electrons and will gain control so bond is now ionic.

Question 7

non-polar bonds

Answer 7

bonded pair of electrons shared equally between bonded atoms so purely covalent.
happens when bonded atoms are same e.g H2 or when similar electronegativities

Question 8

polar bonds

Answer 8

when electronegativity of two atoms are different causes polarisation , causing electronegative and electronegative atoms (permenant dipoles)

Question 9

Polar molecules

Answer 9

if a molecule has several polar bonds and they all act in different direactions (e.g outwards) the cancel and the molecule is non polar with polar bonds - symmetrical

if the dipoles act in the same direction (towards one point) the molecule is polar - non-symmetrical

Question 10

what is intermolecular bonding

Answer 10

covalent bonding holds atoms in a molecule together whereas intermolecular forces are interactions between dipoles of different molecules

-London forces (induced-induced)
-permenant-permenant
hydrogen bonding

Question 11

London forces

Answer 11

weak intermolecular forces that exist between all molecules
- constant movement of electrons produces a n
oscillating dipole
- at any moment, an instantaneous dipole will exist
- the instantaneous dipole induces a dipole on a
neighbouring molecule

Question 12

what affects london forces

Answer 12

the more electrons in each molecule

• the larger the instantaneous and induced dipole
• the stronger the induced-induced dipole interaction
• the stronger the London forces
• more energy needed to overcome forces increasing the boiling point

Question 13

permenant dipole-permenant dipole

Answer 13

between permenant dipoles of molecules

having both London and permenant dipole interactions increase bp compared to just London forces

Question 14

simple molecular substance (covalent)

Answer 14

atoms within each molecule bonded by strong covalent bonds

molecules are held in place with weak IMF

Question 15

bp of simple molecular

Answer 15

low melting and boiling points because weak IMF forces can be broken

Question 16

simple molecular solubility

Answer 16

non polar and polar simple molecular substances
non polar in non polar: IMF form between solvent and molecules so IMF in substance breaks and compound dissolves
non polar in polar: little interaction between molecules in lattice and solvent so IMF in polar substance too strong to be broken
polar in polar: may dissolve

Question 17

hydrogen bond

Answer 17

between lone pair of electrons on an electronegative atom and a hydrogen atom - strongest IMF

Question 18

properties of water due to hydrogen bonding

Answer 18

solid ice is less dense than water because hydrogen bonds hold water molecules apart in an open tetrahedral lattice structure so water molecules further apart so less dense -forms insulating layer

water has high melting and bp - strong H bonds as well as London forces so more energy needed to break them

high surface tension

Question 19

giant covalent properties

Answer 19

• high melting and boiling point as high temp needed to
  break the strong covalent bonds in the lattice
• non conductors of electricity except graphite
• not soluble as too strong to be broken by polar or non
  polar solvents

Question 20

diamond vs graphite

Answer 20

diamond:
symmetrical structure held by strong covalent bonds
poor electrical conductivity as no delocalised electrons
hard as tetrahedral shape makes it strong

graphite:
strong layer structure but with weak bonds between layers
good conductivity as delocalised electrons can move between layers
soft as bonding within each layer is strong but weak forces between layers means they can slide