3.Bonding

Question 1

What is ionic bonding

Answer 1

The electrostatic forces between oppositely charged ions in a giant lattice

Question 2

Name properties of ionically bonded compounds

Answer 2

• solid at room temperature
• high melting point as they are giant structures as electrostatic forces extends throughout the compound
• conduct when molten or dissolved
• brittle

Question 3

What is a covalent bond

Answer 3

A shared pair of electrons

Question 4

How does sharing electrons hold atoms together

Answer 4

Atoms within a covalent bond are held together by the electrostatic attraction between the nuclei and shared electrons

Question 5

What are properties of covalently bonded molecules

Answer 5

• low melting point due to weak intermolecular forces

- don’t conduct electricity

Question 6

What is dative covalent bonding

Answer 6

Covalent bonding in which both electrons come from one atom in the bond.

Question 7

Which are stronger covalent or dative

Answer 7

Neither, they are the same strength

Question 8

What is metallic bonding

Answer 8

The electrostatic attraction between lattice of positive ions and a sea of delocalised electrons

Question 9

What does metallic bonding’s strength depend on

Answer 9

• charge of the ion, greater the positive charge, greater the number of delocalised electrons, stronger the electrostatic attraction
• size if the ion, the smaller the ion the closer the delocalised electrons are to the positive nucleus

Question 10

What kind of structure is metal

Answer 10

Giant lattice structure

Question 11

Describe properties of metals

Answer 11

• can conduct electricity due to delocalised electrons
• good conductors of heat due to sea of electrons
• malleable and ductile
• high melting points as they are giant structures

Question 12

Define electronegativity

Answer 12

The power of an atom to attract the electron density in a covalent bond towards itself

Question 13

What does electronegativity rely on

Answer 13

• nuclear charge
• the distance between the nucleus and the outer shell electrons
• the shielding

Question 14

Describe the trend in electronegativity up a group

Answer 14

• electronegativity increases

- there is less shielding by electrons in inner shells

Question 15

Describe the trend in electronegativity across a period

Answer 15

• electronegativity increases

- nuclear attraction increases for the same amount of shielding

Question 16

What is polarity

Answer 16

Unequal sharing of electrons between atoms that are bonded covalently

Question 17

When atoms in a covalent bond have a large difference in electronegativity the bond is said to be

Answer 17

Polar

Question 18

Name the 3 intermolecular forces in order of strength

Answer 18

• van der Waals
• Dipole-dipole
• Hydrogen bonding

Question 19

What is a dipole-dipole force

Answer 19

An intermolecular force that results from the attraction between molecules with permanent dipoles

Question 20

What is a dipole moment

Answer 20

Sums up the effect of the polarity of all the bonds in the molecule

Question 21

What are van der Waals forces

Answer 21

An intermolecular force of attraction between instantaneous dipole and induced dipole and acts between all molecules

Question 22

How are instantaneous dipoles caused

Answer 22

The dipole is caused by the changing position of an electron cloud

Question 23

Why are van der Waals sometimes called instantaneous dipole-induced dipole forces

Answer 23

As the electron distribution of the original atom changes it will induce new dipoles in the atoms around it

Question 24

What causes a larger van der Waal force

Answer 24

The number of electrons present so atoms or molecules with large atomic or molecular masses produce stronger van der Waals

Question 25

Using the idea of van der Waal forces explain why the boiling point of noble gases increase down the group

Answer 25

- as you go down the group the atomic numbers of the noble gases increase - this is because there are more electrons present - this causes larger instantaneous dipoles - larger van der Waal forces

Question 26

Using the idea of van der Waal forces explain why the boiling points of hydrocarbons increase with chain length

Answer 26

- as hydrocarbons increase in chain length - larger surface area so more points of contact with adjacent molecules - this means more van der Waals forces are instantaneously formed

Question 27

What is hydrogen bonding

Answer 27

An intermolecular force in which a H d+ atom interacts with a more electronegative atom with a d- charge

Question 28

When do hydrogen bonds form

Answer 28

- a hydrogen atom that is bonded to a very electronegative atom. This produces a strong partial charge - a very electronegative atom with a lone pair of electrons. These will be attracted to the partially charged H atom.

Question 29

What are the only atoms that are electronegative enough to form hydrogen bonds

Answer 29

- O - N - F

Question 30

Why is water denser than ice

Answer 30

- in water molecules can move around - in ice molecules can no longer move around, the hydrogen bonds hold a fixed position - this results in a 3D structure - to fit into this structure molecules are slightly less packed - this means ice is less dense

Question 31

Using the idea of intermolecular forces describe how ironing works

Answer 31

- iron provides heat to break hydrogen bonds - pressure forces molecules to be flat - when you remove iron hydrogen bonds reform and hold the molecules in the new positions

Question 32

What is electron pair repulsion theory

Answer 32

- explains the shape of molecules - each pair of electron around an atom will repel all other electrons - the pairs of electrons will therefore take up positions as far apart as possible to minimise repulsion

Question 33

Shape of molecule: two pairs of electrons

Answer 33

Linear. 180°

Question 34

Shape of molecule: three pairs of electrons

Answer 34

Trigonal planar. 120°

Question 35

Shape of molecule: four pairs of electrons

Answer 35

Tetrahedron. 109.5°

Question 36

Shape of molecule: five pairs of electrons

Answer 36

Trigonal bipyramid. 90° (same plane) 120° on different.

Question 37

Shape of molecule: six pairs of electrons

Answer 37

Octahedral. 90°

Question 38

What is the effect of a lone pair of electrons.

Answer 38

Reduces the bond angle by 2.5°

Question 39

Why is the bond angle reduced by lone pairs

Answer 39

- lone pairs are only attracted by one nucleus - therefore are pulled closer to the nucleus and other electrons - electron repulsion theory, paired electrons are repelled further reducing angle by 2.5

Question 40

What is the order of electron pair repulsion strength.

Answer 40

bp-bp< bp lp< lp lp

Question 41

What is enthalpy change of melting/vaporisation

Answer 41

Energy required to weaken the forces holding a element in a solid (liquid) state resulting in a liquid (gas)

Question 42

What are crystals

Answer 42

Solids with a regular arrangement of particles held together by forces (covalent, ionic or metallic or weaker IMF)

Question 43

Name the 4 basic types of crystals

Answer 43

- ionic - metallic - molecular - macromolecular

Question 44

Which two types of compounds exist as crystals

Answer 44

Ionic and metallic (lattices)

Question 45

Molecular crystals

Answer 45

- held together by IMF | - low melting points as IMFs are weak

Question 46

Name 3 macromolecular crystals

Answer 46

- diamond - graphite - buckminsterfullerene

Question 47

Diamond

Answer 47

- each electron in carbon atoms outer shell is bonded with another carbon atom - bond angles of 109.5 - forms a giant 3D lattice of covalent bonds - very hard - very high melting - does not conduct electricity

Question 48

Graphite

Answer 48

- each carbon forms 3 covalent bonds - bond angle 120 - 1 delocalised electron for each carbon free to move within graphene layer - layers of graphene held by weak van der Waals - soft (weak IMF) - high melting (strong covalent bonds in giant structure) - conducts electricity along layers (delocalised electron)