Chemical Bonding

Question 1

Ionic bonding

Answer 1

The electrostatic attraction between oppositely charged ions

Question 2

Giant ionic lattice

Answer 2

A three dimensional structure of oppositely charged ions held together by ionic bonds

Question 3

Properties of ionic compounds

Answer 3

• High melting point and boiling point as ionic bonds are strong and have to all be broken to change states
• Conducts electricity when molten or aqueous as ions are free to move to carry charge
• Dissolves in polar substances. Six O- rip off a cation while 4 H+ rip off the anion
• Don’t dissolve in non-polar solvents
• Don’t conduct electricity as a solid
• Tend to be brittle as when the layers shift, the opposite ions will repel

Question 4

Isoelectronic

Answer 4

To have the same number of electrons e.g. Si4+ is isoelectronic with Ne

Question 5

Covalent bond

Answer 5

The electrostatic attraction between two nuclei and the same shared pair of electrons

Question 6

Lone pair

Answer 6

An outer shell pair of electrons that is not involved in chemical bonding

Question 7

The octet rule

Answer 7

The rule that only 8 electrons occupy one shell when bonding with other atoms

Question 8

Dative covalent bond

Answer 8

A covalent bond formed when a lone pair has been provided by one of the bonding atoms

Question 9

Properties of diamond

Answer 9

• Doesn’t conduct electricity as there are no free charge carriers available
• Giant covalent lattice
• Tetrahedral C arrangement
• Bare hard as covalent bonds are strong and a lot of energy is needed to break them all

Question 10

Properties of graphite

Answer 10

• Giant covalent structure
• Conducts electricity as there is a layer of delocalised electrons between the C layers that can carry charge
• C arranged in layers
• Layers can slide over each other so graphite can acts as a lubricant

Question 11

Allotrope

Answer 11

Refers to one or more forms of an elementary substance

Question 12

Metallic bonding

Answer 12

The electrostatic attraction between cations and a sea of delocalised electrons

Question 13

Properties of metals

Answer 13

• High melting and boiling points as there is a large electrostatic attraction between the cations and the delocalised electrons
• Good conductors as delocalised electrons can carry charge
• Even better conductors when molten as the cations can carry charge too
• Insoluble in water or non-polar substances as the metallic bonds are too strong relative to intermolecular forces
• Malleable
• Ductile

Question 14

Trend in mp/bp of metals (I,II,III)

Answer 14

• Increases along the group as the number of electrons are increasing and the charge on the cations are too
• Decreases down a group as the outer electron is far from the nucleus and can be removed easily

Question 15

Malleability

Answer 15

The ability to change shape without breaking

Question 16

Ductility

Answer 16

The ability to be pulled into a thin wire

Question 17

Alloys

Answer 17

A mixture of metals; not a compound
E.g. stainless steel = steel + chromium
Brass = copper + zinc

Question 18

Use of alloys

Answer 18

Alloys make metals harder as the ions sizes of the metals are different, so the layers cannot slide over each other

Question 19

Valence Shell Electron Pair Repulsion theory

Answer 19

Each bonded pair repel themselves so they are as far away from eachother
Lone pairs repel more than bonding pairs

Question 20

Linear

Answer 20

e.g. BeCl2
2 bonding pairs 0 lone pairs
bond angle 180 degrees

Question 21

Trigonal planar

Answer 21

e.g. BF3
3 bonding pairs 0 lone pairs
bond angle 120 degrees

Question 22

Tetrahedral

Answer 22

e.g. CH4
4 bonding pairs 0 lone pairs
bond angle 109.5 degrees

Question 23

Trigonal pyramid

Answer 23

e.g. NH3
3 bonding pairs 1 lone pair
bond angle 107 degrees

Question 24

Bent

Answer 24

e.g. H2O
2 bonding pairs and 2 lone pairs
bond angle 104.5 degrees

Question 25

Octahedral

Answer 25

e.g. SF6 6 bonding pairs 0 lone pairs bond angle 90 degrees

Question 26

The three types of intermolecular force

Answer 26

van der Waals' Permanent dipole-dipole Hydrogen bonding

Question 27

How do van der Waals' forces arise?

Answer 27

Electrons are constantly moving. At any instant, the distribution may not be symmetrical. This results in an instantaneous temporary dipole. This dipole induces dipoles in neighboring molecules and leads to an attraction between the opposite charges in the dipoles

Question 28

Factors that affect the van der Walls' force

Answer 28

- Number of electrons - the more the stronger - The weaker the contact area, the stronger the induced dipole - Unbranched molecules have stronger van der Waals' forces

Question 29

Trends in group VII

Answer 29

State progressively changes from gas to solid down the group Reactivity decreases down the group Mp/Bp increases down the group

Question 30

Electronegativity

Answer 30

The ability of an atom to attract electrons to itself in a bond

Question 31

Electronegativity's of some elements

Answer 31

``` F=4 O,N=3.5 Cl=3 Mg=1.2 Na=0.9 Al=1.5 ```

Question 32

Permanent dipole

Answer 32

A small charge difference across a bong resulting from a difference in electro-negativities of the bonded atoms Permanent dipole-dipole attractions occur in addition to van der Waals' forces

Question 33

Trend in electronegativity

Answer 33

Electronegativity increases across a period and decreases down a group

Question 34

Use of electronegativity

Answer 34

Electronegativity can be used to predict bonding type Electronegativity > 2.0 usually ionic Electronegativity 1.0~2.0 usually polar Electronegativity < 1.0 usually covalent

Question 35

Relative strengths of bonds and intermolecular forces

Answer 35

Ionic/covalent bonds 1000 Hydrogen bonds 50 Permanent dipole-dipole attraction 10 Van der Waals' 1

Question 36

Polar covalent bond

Answer 36

A covalent bond with a permanent dipole

Question 37

Polar molecule

Answer 37

A molecule with an overall dipole when you take into account any dipoles across the bond

Question 38

When drawing hydrogen bonded molecules

Answer 38

Draw the hydrogen bond with a striped line Draw the delta + and - Position atoms either side of the H+ as far away from each other Draw any lone pairs

Question 39

Hydrogen bonds

Answer 39

The attraction between a hydrogen atom on one molecule and a lone pair of another O, N or F molecule

Question 40

The reason water is not like the other Group VI hydrides

Answer 40

All group VI hydrides have a van der Waals' attraction. On top of this, water has hydrogen bonding so its mp/bp are different

Question 41

The reason ice floats on water

Answer 41

In a solid, water forms a rigid structure held apart by hydrogen bonds. When this structure melts, the rigid hydrogen bonds break and the molecules move closer together