CH2: Structure

Question 1

What is electronegativity?

Answer 1

Power of an atom to attract the pair of electrons in a covalent bond towards itself

Question 2

How does nuclear charge effect electronegativity?

Answer 2

• attraction between protons in nucleus and electrons on outer shell
• this attraction increases when no. Protons in nucleus increases
• increased NUCLEAR CHARGE , INCREASED ELECTRONEGATIVITY

Question 3

How does the atomic radius effect electronegativity?

Answer 3

Electrons closer to nucleus - more strongly attracted to positive nucleus

an increased atomic radius results in a decreased electronegativity

Question 4

How does shielding effect electronegativity?

Answer 4

• filled shells can Shield the effect of nuclear charge —> outer electrons are less attracted to nucleus
  an increased number of inner shells and subshells will result in a decreased electronegativity

Question 5

Trend of electronegativity down the group?

Answer 5

DECREASE in electronegativity
1) nuclear charge increases
2) HOWEVER , the elements have more SHELLS as you go down the group —> INCREASE SHIELDING/RADIUS

Question 6

Trend in electronegativity across a period ?

Answer 6

INCREASES
- nuclear charge increases
- shielding is constant (all have same no. Shells/sub shells))
- so as the attraction between nucleus and outer electrons is strong , ATOMIC RADII DECREASES

Question 7

When is the covalent bond NON POLAR?

Answer 7

When tow atoms have same electronegativity

Question 8

How does the difference in electronegativities determine the bond formed?

Answer 8

• when difference between electronegativities is more than 1.7 - IONIC BOND and ions formed
• when difference is 0.3 to 1.7 - COVALENT BOND and is POLAR

Question 9

Which part of the atom will be positive and which art will be negative if the atom is POLAR?

Answer 9

Less electronegative atom - delta positive
More electronegative atom- delta negative

Question 10

How to determine the polarity of a molecule?

Answer 10

• the polarity of each bond
• how the bonds are arranged in the molecule (if symmetrical - not polar)

Question 11

What is metallic bonding?

Answer 11

• lattice structure of positive charge in a ‘sea’ of delocalised electrons held by electrostatic forces between opposite charges

Question 12

Properties of GRAPHITE ?

Answer 12

CONDUCT ELECTRICITY : each atom bonded to 3 others, so 1 DELOCALISED

SOFT AND SLIPPERY : weak intermolecular forces between layers - can slide

Question 13

Structure of DIAMOND?

Answer 13

each carbon bonds with 4 others —> TETRAHEDRON

• NO INTERMOLECULAR FROCES

Question 14

Structure of GRAPHENE?

Answer 14

Single layer of graphite - one atom thick

Question 15

Solubility of all structures?

Answer 15

GIANT IONIC : soluble
GIANT METALLIC : insoluble
SIMPLE COVALENT : insoluble unless polar
GIANT COVALENT : insoluble

Question 16

What are van der waal forces?

Answer 16

• exist between all atoms/molecules
  Weak intermolecular forces arising due to fluctuations in electron density in a non polar molecule
• electron charge cloud in non polar molecules move constantly —> causes temporary dipole
• temporary dipole can induce a dipole on neighbouring molecules
• δ+ end of the dipole in one molecule and the δ- end of the dipole in a neighbouring molecule are attracted towards each other

Question 17

What are permanent dipole forces?

Answer 17

• between polar molecules (have both. Negative and positive charged end)
• oppositely charged ends attract

Question 18

What makes London forces stronger?

Answer 18

• more electrons so stronger London forces

Question 19

Trend in BP in group 6 hydrides ?

Answer 19

• enthalpy of vaporisation increase from H2S to H2Te due to increased no. Electrons = larger London forces
  Water doesn’t follow this pattern - enthalpy change of vaporisation larger than hydrides due to Hydrogen Bonds in water but not in other hydrides

Question 20

BP trend in group 7 hydrides?

Answer 20

HF molecules form hydrogen bonds with each other - highest BP
From HCl to HI, BP increases due to more electrons = strength of London forces increases

Question 21

When do hydirgen bonds occur?

Answer 21

When hydrogen is covakently bonded to FLUORINE, NITROGEN AND OXYGEN
- form bonds with lone pairs of electrons on fluorine, oxygen and nitrogen

Question 22

Why is ice less dense than water?

Answer 22

In ice , water molecules are arranged so there is max number of H bonds - lattice ‘wastes’ space
- arranged so more space between molecules - longer bond lengths - less dense

When melted , some hydrogen bonds are broken/lattice breaks down - molecules ‘fill’ spaces

Question 23

When will a substance dissolve?

Answer 23

Strength of new bonds formed is same as/greater than strength of bonds broken

Question 24

2 types of solvent?

Answer 24

Polar solvents - e.g water - molecules bond by H bonds / can only form London forces/permanent dipole forces

Non polar solvents - e.g hexane
- hexane molecules bond together by London forces

Question 25

How do ionic substances dissolve in polar solvents ?

Answer 25

Ions attracted to oppositely charged ends of water molecules
- ions pulled away from ionic lattice by water molecules , which surrounds ions - HYDRATION

They will dissolve if enthalpy change of hydration is greater than/closer to energy needed to break up lattice

Some ionic substances don’t dissolve bc bonding of ions too strong

Question 26

How do alcohols dissolve in polar solvents ?

Answer 26

Bc polar O-H bond attracted to O-H bonds in water - form hydrogen bonds to lone pairs on oxygen

Carbon chain isn’t attracted to water so more C atoms there are , the less soluble alcohol will be

Question 27

Why don’t all molecules with polar bonds dissolve in water?

Answer 27

Halogenoalkanes have polar bonds but DIPOLES aren’t strong enough to form H BONDS with water
- hydrogen bonding in water is stronger than bonds that would be formed with halogenoalkanes

However form permanent dipole forces so dissolve in polar solvents that form permanent dipole forces

Question 28

What substances tend to dissolve best in non polar solvents?

Answer 28

Non polar substance - form similar bonds (London forces)

Question 29

Size of O-H-O angle in water ?

Answer 29

180 degrees