3.1.3 Bonding

Question 1

Ionic Bonding:

Groups and charges formed required.

Answer 1

Ionic compounds are oppositely charged ions held together by electrostatic attraction

G1 = 1+ ions
G2 = 2+ ions
G3 = 3+ ions

G5 = 3- ions
G6 = 2- ions
G7 = 1- ions

Question 2

Molecular ions.

Answer 2

OH- = hydroxide
NO3- = nitrate
NH4+ = ammonium
So42- = sulfate
CO32- = carbonate

Question 3

Swap and drop method: Ca^2- and NO3^-

Answer 3

Ca^2- and NO3^-
Swap the charges: Ca^- and NO3^2-
Drop the charges: Ca and (NO3)2
Simplify to lowest whole number ratio (if needed): Ca(NO3)2

Question 4

Swap and drop method: Ca^2+ and O2^-

Answer 4

Ca^2+ and O^2-

Swap the charges: Ca^- and O^2+
Drop the charges: Ca2 and O2
Simplify to lowest whole number ratio (if needed): Ca2O2 = CaO

Question 5

Physical properties of compounds with ionic bonding.

Answer 5

1. Dissolve in water as water molecules are polar, can attract the positive and negative ions to break up the structure.
2. Conduct electricity when molten or dissolved in solution as ions are free to move around.
3. High mp = many strong electrostatic forces between oppositely charged ions. Lots of energy needed to break the bonds.

Question 6

Covalent bond.

Answer 6

Sharing of outer electrons in order to for atoms to obtain a full outer shell.

Electrostatic force of attraction between the shared electrons and the positive nucleus.

Can be single, double or triple covalent bonds. = more electrons being shared.

Can be represented by lines too.

Question 7

Dative covalent bonding or coordinate bonding.

Answer 7

When one atom donates 2 electrons to an atom or ion to form a bond. i.e NH3 forms a dative covalent bond with H+ as nitrogen donates to 2 electrons to the H+ and forms
H+
^
HNH
H

Question 8

Giant covalent structures.

Answer 8

Graphite:
C = bonded x3 with 4th electron delocalised.

Layers can slide easily = weak forces between layers.

Delocalised electrons between layers = conduct electricity = carry a charge.

Low density = layers far apart compared to covalent bond length.

High mp = lots of strong covalent bonds

Insoluble = covalent bonds are too strong to break.

Diamond:
C = bonded x4 in tetrahedral shape.

Conduct heat well = tightly packed and rigid structure.

Can be cut into gemstones unlike diamond.

Very high mp = mant strong covalent bonds = very hard.

Doesn’t conduct electricirty = no delocalised electrons.

Insoluble = Covalent bonds too strong to break.

Question 9

Why do molecules have a specific shape with specific angles?

Answer 9

Bonds repel each other equally
bonds contain electrons so they will want to be as far apart as possible.

Question 10

Does a lone pair or bond pair repel more?

Answer 10

Lone pair.
Lp push bp closer together
Generally each lp reduce remaining bonding angle by 2.5 *

Lone pair next to 2 bp repel more:
109 * (with no lp and 4x just bp)
107 * (with one lp and 3x bp)
104.5 * (with two lp and 2 bp)

Question 11

How many bp and lp NH4^+ has

shape with no lone pairs.

Answer 11

With IONS add electrons if negative ion and minus if positive ion.

NH4^+
Nitrogen has 5 electrons but now has 4 bp only.

BP = 4
LP = 0
Total = 4
Name: Tetrahedral.

Question 12

How many bp and lp H2O has

shape with lone pairs.

Answer 12

Based on tetrahedral but has 2 lp.
Angle reduced by 2.5 * = 5*

BP = 2
LP = 2
Total = 4

Question 13

Electronegativity

Answer 13

Ability for an atom to attract electrons towards itself in a covalent bond.

Further and up right you go (excluding noble gas) the more EN element is.

Fluroine = most EN

Question 14

Electronegativity = pauling scale.

Answer 14

Element = EN
H = 2.0
C = 2.6
N = 3.0
Cl = 3.0
O = 3.4
F = 4.0

Bigger the difference in EN the more polar the bond is.

Question 15

Polar bonds.

Answer 15

Covalent bonds become polar if the atoms attached to it have a difference in EN

The bigger the difference the more polar the bond will be.

symmetrical polar bonds i.e CO2 = C = delta + O2= delta - but have no overall polarity due to symmetrical arrangement.

Question 16

Van der waals

Answer 16

induced dipole dipole
forces that exist between atoms and molecules.
Can hold some molecules in a crystal structure i.e. iodine = I2

Question 17

Intermolecular forces strength.
strongest to weakest

Answer 17

Hydrogen bonding
permenant dipole dipole
Van der waals

Question 18

Why would you have more VDW forces in a bigger molecule or atom?

Answer 18

The larger the electron clouds are.

Question 19

When boiling a liquid for example bromine what forces do we break?

Answer 19

VDW forces not covalent bonds.
There must be enough energy to overcome these forces.

Question 20

Between long straight hydrocarbon chains and branched hydrocarbons which one requires more energy to break the bonds?

Answer 20

Long straight hydrocarbons = more VDW forces, more energy required to overcome the forces, bp increases

Branched can’t pack closely together, weakens VDW forces between chains, lower bp.

Question 21

Permenant dipole dipole

Answer 21

exist in molecules with polarity.
stronger than VDW.
molecules with permenant dipole dipole also have VDW forces.
Will be weak electrostatic forces between molecules with a polarity.

Question 23

How to test polar molecules like water

Answer 23

place a charged rod near steady stream of polar liquid.
Liquid will bend towards to charged rod as molecules align to face the oppositely charged rod.

Question 24

Hydrogen bonding

Answer 24

strongest intermolecular force and occurs when you have EN elements.
FON forms hydrogen bonding.
represented by dotted line between lp and hydrogen
also contain permenant dipole dipole and VDW

Question 25

Why is ice less dense than water?

Answer 25

regular structure held by hydrogen bonding. molecules are futher apart which is what makes it less dense than water.

Question 26

Boiling points of hydrogen halides.

Answer 26

**HF** has a higher boiling point than HCl = more hydrogen bonding. more energy required to overcome the electrostatic forces. **HCl to HI** increase in bp due to increase mass of molecule = bigger electron cloud = more VDW forces

Question 27

Metallic bonding.

Answer 27

giant metallic structures. + metal ion formed as metals **donate electrons** to form a sea of delocalised electrons. **Electrostatic attraction** between positive metal ion and negative delocalised electrons. More electrons an atom can donate to delocalised system = higher mp i.e. Mg has higher mp than Na as Mg can donate 2 electrons but sodium can donate 1 electron.

Question 28

Physical properties of metallic bonding.

Answer 28

Good thermal conductors = delocalised electrons can transfer KE High melting points = strong electrostatic forces of attraction. Solid metals are insoluble = metallic bond too strong to break. Good electrical conductors = delocalised electrons mobile and can carry a current.