Topic 2 Bonding and Structure

Question 1

What are the two different types of bonds?

Answer 1

Chemical (strong) and Physical (weak)

Question 2

What bonds are chemical?

Answer 2

Ionic, Metallic, Covalent and Dative Covalent

Question 3

What bonds are physical?

Answer 3

London Forces (weakest), Dipole-Dipole and Hydrogen bonds (strongest)

Question 4

What is the definition of ionic bonding?

Answer 4

The strong electrostatic attraction between oppositely charged ions.

Question 5

What happens in ionic bonding?

Answer 5

Electrons are transferred between atoms. These atoms are usually metal and non-metal.

In the case of sodium chloride, sodium would lose an electron which is transferred to the chlorine resulting in to ions with full outer shells.

Question 6

What are positive ions?

Answer 6

• Also known as Cations
• Smaller than original atom
• Formed when electrons are removed from atoms
• The energy associated with this is ionisation energy
• Successive ionisation energies get higher as the proton:electron ratio gets bigger

Question 7

What are negative ions?

Answer 7

• Also known as Anions
• Bigger than the original atom
• Formed when electrons are added to atoms
• Energy associated with this is electron affinity (the energy released when the nucleus pulls in an electron)

Question 8

What is a Giant Ionic Crystal Lattice?

Answer 8

When oppositely charged ions are held in a regular 3-dimensional lattice by electrostatic attraction.

Question 9

What are the properties of ionic compounds?

Answer 9

• Very High Melting Point: A large amount of energy must be put in to overcome the strong electrostatic attractions and separate the ions.
• Very brittle: Any dislocation leads to the layers moving and similarly charged ions being next to each other. The repulsion splits the crystal.
• Conductivity: do not conduct when solid - ions are held strongly in the lattice. Conduct when molten or in aqueous solution - the ions become mobile and conduction takes place.
• Solubility: Insoluble in non-polar solvents but soluble in water. Water as it is a polar solvent and stabilises the separated ions.

Question 10

What is the definition of Covalent Bonding?

Answer 10

When atoms share a pair of electrons with one electron being supplied by each atom either side of the bond.

Question 11

What is the Orbital Theory for Covalent Bonding?

Answer 11

Covalent bonds are formed when orbitals, each containing one electron, overlap. This forms a region in space where an electron pair can be found; new molecular orbitals are formed.

The larger the overlap the stronger the bond.

Question 12

What are Dative Covalent Bonds?

Answer 12

A covalent bond where both electrons of the shared pair are provided by one species (donor) and it shares the electrons with the acceptor.

• Donor species will have lone pairs in their outer shells
• Acceptor species will be short of their “octet” or maximum.
• Then donor atoms becomes positively charged and the acceptor becomes negatively charged.

Question 13

What are the properties of covalent molecules?

Answer 13

• Bonding: Atoms are joined together within the molecule by covalent bonds.
• Conductivity: Don’t conduct electricity as they have no mobile ions or electrons
• Solubility: Tend to be more soluble in organic solvents than in water; some are hydrolysed

Question 14

What is electronegativity?

Answer 14

The ability of an atom to attract the pair of electrons in a covalent bond to itself.

Question 15

What is the Pauling scale?

Answer 15

A scale for measuring electronegativity.

Question 16

What are non-polar bonds?

Answer 16

Bonds between atoms with similar electronegativity in which they will both pull on the electrons to the same extent the electrons will be equally shared.

Question 17

What are polar bonds?

Answer 17

Bonds between atoms with different electronegativities in which one will pull the electron pair closer to its end it will be slightly more negative than average, 𝛿- the other atom will be slightly less negative, or more positive, 𝛿+ a dipole is formed and the bond is said to be polar the greater the electronegativity difference, the greater the polarity.

Question 18

What are Instantaneous dipole-induced dipole forces?

Answer 18

Also known as London Dispersion Forces or van der Waals Forces are the intermolecular forces that exist between all molecules. They arise from the attractions between temporary instantaneous dipoles and the fleeting dipoles they induce in neighbouring molecules.

Question 19

What is dipole-dipole interaction?

Answer 19

This occurs between molecules containing polar bonds and acts in addition to the basic London forces. The extra attraction between dipoles means that more energy must be put in to separate molecules resulting in higher boiling points than expected for a given mass.

Question 20

What is hydrogen bonding?

Answer 20

This is an extension of dipole-dipole interactions of which hydrogen atoms bond with the three most electronegative elements - Fluorine, Oxygen and Nitrogen.

Question 21

What are the properties of Giant Covalent Lattices?

Answer 21

• Very high Melting Point: Structures are made up of a large number of covalent bonds, all of which need to be broken if the atoms are to be separated.
• Conductivity: Don’t conduct electricity - have no mobile ions or electrons but… Graphite conducts electricity.
• Strength: Hard - exists in a rigid tetrahedral structure. Diamond and silicon (IV) oxide (SiO2)… but Graphite is soft.

Question 22

What is Metallic Bonding?

Answer 22

The electrostatic attraction between positive metal ions and a ‘sea’ of delocalised electrons.

Question 23

What factors affect electronegativity?

Answer 23

• Nuclear charge: More protons, stronger attraction between nucleus and bonding pair of electrons.
• Atomic radius: Closer to the nucleus, stronger attraction between nucleus and bonding pair of electrons.
• Shielding: Less shells of electrons between the nucleus and the electrons, less shielding (less repulsion), stronger attraction between nucleus and bonding pair of electrons.

Question 24

What is the trend in electronegativity down a group?

Answer 24

It decreases as:

• Atomic radius increases.
• More shielding there less attraction between nucleus and bonding pair of electrons.

Question 25

What is the trend in electronegativity along a period?

Answer 25

Electronegativity increases because:

- More nuclear charge therefore stronger attraction between nucleus and bonding pair of electrons.

Question 26

What are the bond angles you need to know?

Answer 26

104.5, 107, 109.5, 120, 180

Question 27

What are the different shapes of molecules?

Answer 27

• Linear: 2 EP - 2 BP, 0 LP
• Trigonal Planar: 3 EP - 3 BP, 0 LP (5 EP - 3 BP, 2 EP)
• Bent: 3 EP - 2 BP, 1 LP (4 EP - 2 BP, 2 LP)
• Tetrahedral: 4 EP - 4 BP, 0 LP
• Trigonal Pyramidal: 4 EP - 3 BP, 1 LP
• Trigonal Bi-pyramidal: 5 EP - 5 BP, 0 LP
• Octahedral: 6 EP - 6 BP, 0 LP
• Square Pyramid: 6 EP - 5 BP, 1 LP
• Square Planar: 6 EP - 4 BP, 2 LP