chapter 6

Question 1

electron pair repulsion theory

Answer 1

• electron pairs surrounding the central atom determine the shape
• electron pairs repel each other so that they are as far apart as possible
• the arrangement minimises repulsion, holding the bonded atoms into a definite shape

Question 2

lone pair repulsions

Answer 2

lone pairs repel more strongly than bonding pairs. the angle is reduced by 2.5 for each lone pair.

Question 3

4 bonding pairs, 0 lone pairs

Answer 3

tetrahedral

109.5

Question 4

3 bonding pairs, 1 lone pair

Answer 4

pyramidal

107

Question 5

2 bonding pairs, 2 lone pairs

Answer 5

non- linear

104.5

Question 6

shapes from multiple bonds

Answer 6

each multiple bond is treated as one bonding region

Question 7

2 bonding regions

Answer 7

linear

180

Question 8

3 bonding pairs

Answer 8

trigonal planar

120

Question 9

6 bonding pairs

Answer 9

octahedral

90

Question 10

electronegativity

Answer 10

the attraction of a bonded atom for the pair of electrons in a covalent bond

Question 11

3 most electronegative elements

Answer 11

NOF (Cl)

fluorine is the most

Question 12

electronegativity and bonding

Answer 12

can be used to estimate the type of bonding
covalent- 0
polar covalent- 0-1.8
ionic- greater than 1.8

Question 13

non-polar bonds

Answer 13

the bonded electron pair is shared equally between the bonded atoms, when:
the bonded atoms are the same or have the same/similar electronegativity

Question 14

polar bonds

Answer 14

the bonded electron pair is shared unequally between bonded atoms. A bond will be polar when the bonded atoms are different and have different electronegativity values resulting in a polar covalent bond.

Question 15

polar bonds- hydrogen chloride

Answer 15

• the chlorine atom is more electronegative than the hydrogen
• the chlorine atom has a greater attraction for the bonded pair of electrons– polar covalent bond
• this separation of charges= a dipole
• in a covalent bond it is a permanent dipole

Question 16

polarity

Answer 16

if the molecule is symmetrical then the dipoles cancel and it is not polar

Question 17

intermolecular forces

Answer 17

weak interactions between dipoles of different molecules

responsible for physical properties

Question 18

type of bond in order of strength (H, covalent, London & permanent dipoles)

Answer 18

strongest- covalent

• hydrogen bonds
• permanent dipole-dipole interactions
• London forces

Question 19

London forces

Answer 19

weak intermolecular forces that exist between all molecules, they act between induced dipoles in diff molecules.

Question 20

origin of London forces

Answer 20

• movement of electrons produces a changing dipole in a molecule
• an instantaneous dipole but its position is constantly shifting
• the instantaneous dipole induces a dipole on a neighbouring molecule
• the induced dipole induces further dipoles on neighbouring molecules, which attract one another

Question 21

strength of London forces

Answer 21

the more electrons in each molecule:

• the larger the instantaneous & induced dipoles
• the greater the induced dipole-dipole interactions
• the stronger the attractive forces between molecules
• more energy needed to overcome the intermolecular f forces, increasing the boiling point

Question 22

HCl Vs F2 (Bp)

Answer 22

• fluorine molecules are non-polar and only have London forces
• HCl molecules are polar and have London forces & permanent dipole-dipole interactions
• extra energy needed to break the additional permanent dipole interactions
• Bp of HCl is larger than Fluorine

Question 23

simple molecular substances

Answer 23

made up of simple molecules- small units containing a definite number of atoms w/ a definite molecular formula eg Ne, H2, H20 & CO2

Question 24

simple molecular lattice

Answer 24

• molecules held together by weak intermolecular forces

- atoms within each molecule are bonded together strongly by covalent bonds

Question 25

properties of simple molecular substances (mp & bp)

Answer 25

-- low melting & boiling point (weak intermolecular forces easily broken)

Question 26

solubility of non-polar simple molecular substances

Answer 26

soluble in non-polar solvents -intermolecular forced form between the molecules and the solvent, the interactions weaken the intermolecular forces in the simple molecular lattice. intermolecular forces break and the compound dissolves if added to a polar solvent there is little interaction, intermolecular bonding in the polar solvent is too strong to be broken- insoluble

Question 27

solubility of polar simple molecular substances

Answer 27

- may dissolve in polar solvents, can attract each other | - depends on strength of dipole

Question 28

electrical conductivity (simple molecular)

Answer 28

no mobile charge carriers = non-conductor

Question 29

hydrogen bond

Answer 29

special type of permanent dipole-dipole interaction found between molecules containing: - an electronegative atom w/ a lone pair of electrons eg NOF - a hydrogen Aton attached to an electronegative atom

Question 30

anomalous properties of water

Answer 30

- ice less dense than water; molecules in ice are held further apart in the lattice - four bonds- open tetrahedral lattice 180 bond angle - high mp & bp, large quantity of h bonds- strong - high surface tension & viscosity