Electrons and bonding

Question 1

What are electron shells?

Answer 1

Electrons have fixed energies, they move around the nucleus in shells or energy levels. Each shell is given the principal quantum number.
Shells are divided into sub-shells, s, p, d, or f.

Question 2

How many orbitals are in each sub-shell?

Answer 2

Each orbital can hold up to 2 electrons.
S - 1 orbital - 2 max electrons.
P - 3 orbitals - 6 max electrons.
D - 5 orbitals - 10 max electrons.

Question 3

How many electrons can each shell hold?

Answer 3

1st - 1s = 2 electrons.
2nd - 2s, 2p = 8 electrons.
3rd - 3s, 3p, 3d = 18 electrons.
4th - 4s, 4p, 4d, 4f = 32 electrons.
2(n^2) where n is the shell number.

Question 4

What are orbitals?

Answer 4

A bit of space that an electron moves in.
Orbitals within the same sub-shell have the same energy.
The two electrons must spin in opposite directions.

Question 5

What are the shapes of different orbitals?

Answer 5

S-orbitals - spherical.
P-orbitals - dumbbell shaped. The three orbitals are at right angles to one another.

Question 6

What is electron configuration?

Answer 6

The number of electrons an atom has, and how they are arranged.

Question 7

What are the rules for electron configurations?

Answer 7

Electrons fill up the lowest energy sub-shells first.
Electrons fill orbitals with the same energy singly before they start sharing.
For the configuration of ions from s and p blocks, add or remove electrons to or from the highest energy occupied sub-shell.

Question 8

How can electron configuration be shortened?

Answer 8

The noble gas before the element, in square brackets.
E.g. Ca 1s2, 2s2, 2p6, 3s2, 3p6, 4s2 can be written [Ar] 4s2.

Question 9

What is Heisenberg’s uncertainty principle?

Answer 9

1927, theorised that you cannot know the speed of an electron and its exact position at the same time.
Scientists now think of orbitals as an area where electrons are most likely to be found.

Question 10

What is ionic bonding?

Answer 10

The electrostatic attraction between positive and negative ions.
It is very strong.
This forms an ionic compound.
Between non-metal and metals.

Question 11

What are giant ionic lattices?

Answer 11

Ionic crystals are giant lattices of ions.
It is giant because it is made up of the same basic unit repeated over and over again.
Each ion is electrostatically attracted in all directions to ions of opposite charge.

Question 12

What is the electrical conductivity of ionic compounds?

Answer 12

Ionic compounds conduct electricity when they’re molten or dissolved, but not solid.
The ions in a liquid are mobile.
In a solid they’re fixed in position by the strong ionic bonds.

Question 13

What are the melting and boiling points of ionic compounds?

Answer 13

High melting and boiling points.
The giant ionic lattices are held together by strong electrostatic forces, so it takes a lot of energy to overcome these forces.

Question 14

What is the solubility of ionic compounds?

Answer 14

Ionic compounds dissolve in water.
Water molecules are polar, so they pull the ions away from the lattice and cause it to dissolve.

Question 15

What are molecules?

Answer 15

Formed when two or more atoms bond together, can be the same or different.
They are held together by strong covalent bonds.

Question 16

What is a covalent bond?

Answer 16

The strong electrostatic attraction between a shared pair of electrons and the nuclei of bonded atoms.
Usually each of the atoms ends up with 8 electrons in its outer shell - very stable.
It is between non-metals.

Question 17

What are examples of double covalent compounds?

Answer 17

Oxygen in O2 have double bonds, as each oxygen has 6 electrons in outer shell, and needs two more.

Question 18

What is an example of a triple bonded covalent compound?

Answer 18

Nitrogen has 5 electrons in its outer shell, so it needs 3 more to have a full shell.
The only way of doing this in N2, is if each nitrogen atom shares three electrons.

Question 19

What is dative covalent bonding?

Answer 19

Normally, atoms share pairs of electrons, with one electron from each atom.
In dative covalent, one of the atoms provides both of the shared electrons.

Question 20

What is an example of dative covalent bonding?

Answer 20

In the ammonium ion, (NH4+) the nitrogen atom donates a pair of electrons to a H.

Question 21

What are exceptions to the octet rule?

Answer 21

In boron trifluoride, boron only has 6 electrons in the outer shell.
In sulphur hexafluoride, sulphur has 12 electrons in its outer shell.
Phosphorus, and silicon can also expand.

Question 22

What is average bond enthalpy?

Answer 22

It measures the energy required to break a covalent bond.
The stronger a bond, the more energy is required to break it, so the greater the bond enthalpy value.

Question 23

What is the electrical conductivity of simple covalent compounds?

Answer 23

Overall covalent molecules are uncharged, so cannot conduct electricity.

Question 24

What are the melting and boiling points of covalent compounds?

Answer 24

The intermolecular forces holding the molecules together are weak so don’t need much energy to break.
So melting and boiling points are low, often liquid or gas at room temp.

Question 25

What is the solubility of covalent compounds?

Answer 25

Water is a polar molecule, so only tends to dissolve other polar substances well.
Compounds with hydrogen bonds can form hydrogen bonds with water, so will be soluble.
Non-polar molecules will be insoluble.