Bonding and Structure

Question 1

Draw dot-and-cross diagram for the reaction between magnesium and oxygen

Answer 1

google it lol

Question 2

Describe the structure of ionic compounds.

Answer 2

They have giant lattice structures, consisting of an array of positive ions and negative ions. which have electrostatic attraction between them. Eg. Na+ and Cl- in sodium chloride.

Question 3

What determines the bond strength between two ions?

Answer 3

The smaller the ions and the larger the ionic charge, the more energy is required to overcome the electrostatic attraction between them and the stronger the ionic bonding.

Question 4

Trend in ionic radii for elements down a group and for isoelectronic atoms from N3- to Al3+?

Answer 4

Down a group the ionic radius increases because the number of quantum shells increases, so the distance between the nucleus and the outermost electrons increases.

For isoelectronic atoms, it depends on the proton number. This is because the higher the proton number, the stronger the nuclear charge. A strong nuclear charge pulls the outermost shell towards the nucleus and decreases the ionic radius.

Question 5

What is polarisation and what does it depend on?

What does polarisation do to an ionic compound?

Answer 5

In an ionic lattice, the positive ions will attract electrons from the anion. When it does that, the anion loses its even distribution of its electron density because it gets distorted. The anion becomes polarised.

Polarisation depends on the size of the cation and the size of its charge, as well as the size of the anion and its charge.

The higher the charge of the cation and the smaller it is, the higher its polarising power.

Anions with a large charge and a small radius are more easily polarised.

Polarisation can give an ionic compound covalent character.

Question 6

What are the properties of ionic compounds?

Answer 6

They have high melting and boiling temperatures because high amounts of energy are required to overcome the electrostatic attraction between the ions.

They are brittle because the layers slide over one another and since ions of the same charge are now layered over each other, they repel and the crystal breaks.

They conduct electricity when molten or aqueous. When molten, ions are free to move and they migrate to the electrodes of opposite charge in electrolysis. They do the same when aqueous as they dissolve in water and become free. Oxidation always happens at the anode.

They are soluble. This is because water molecules are polar and so both positive and negative ions are attracted to them. So the compound dissociates as negatives attract to hydrogen end of water molecules and positives attract to oxygen end.

Question 7

Draw a dot-and-cross diagram for Al2Cl6 and NH4+ ion.

Answer 7

google it

Question 8

Describe the structures of:

1. Graphite
2. Diamond
3. Graphene

and their properties and applications.

Answer 8

Graphite has a layered structure. Each carbon atom is bonded to 3 others, which forms interlocking hexagonal rings. Between layers there is a cloud of delocalised electrons due to the final electron in the p orbitals of each carbon. It has a high conductivity for electricity and a high melting temperature. Used in pencils bc of layers slide over each other and its soft.

Diamond has a rigid structure. Each carbon atom is bonded to 4 others, and this gives diamond its 3D tetrahedral arrangement. It has a high melting temperature because of the strong C-C bonds which require high amounts of heat energy to overcome. Doesn’t conduct electricity because it has no delocalised electrons. Used in cutting tools because sharp and high melting temp.

Graphene is a single layer or sheet of graphite. It is one atom thick, making it very thin and can conduct electricity. It is therefore useful in microelectronics and mobile phones.

Question 9

What is electronegativity?

Answer 9

It is the ability of an atom to attract a bonding pair of electrons.

Question 10

Define bond length and bond strength,

give the relationship between the two?

Answer 10

Bond length is the distance between the nuclei of two covalently bonded atoms.
Bond strength is the energy required to break the bond between two covalently bonded atoms.

The shorter the bond length, the greater the bond strength. This is because when the bond length is short, there is greater electrostatic attraction between the two nuclei and the bonded electrons.

Question 11

According to the EPR theory, what do the bond pairs around the central atom of a molecule do?

Answer 11

They arrange themselves around the central atom so that the repulsion between them is at a minimum.

Question 12

What are the shapes and angles for the no. of bonding pairs: 2, 3, 4, 5, 6 without lone pairs?

Answer 12

2- Linear 180
3- Trigonal planar 120
4- Tetrahedral 109.5
5-Trigonal bipyramidal 90 and 120
6-Octahedral 90

Question 13

What are the shapes and angles for the no. of bonding pairs 2 with 2 lone pairs, 3 with 1 lone pair?

Answer 13

2 with 2- v shaped 104.5

3 with 1- trigonal pyramidal 107

Question 14

Bond angle and shape of C2H4?

Answer 14

planar, 120

Question 15

Properties of metals?

Answer 15

High boiling and melting temperatures, good conductors of electricity, good thermal conductors, malleable, ductile

Question 16

Relate the charge to radius ratio of a metal to its melting temperature.

Answer 16

The higher the charge to radius ratio, the stronger the electrostatic attraction between the cations and the delocalised electrons in the metal. This increases the melting temperature of the metal.