Unit 1- Structure and bonding

Question 1

How are covalent bonds are formed?

Answer 1

A covalent bonds occurs between non-metal elements.
It is a result of two positive nuclei being held together by their common attraction for the shared pair of electrons.

Question 2

What is the description of Polar covalent bonds?

Answer 2

Polar covalent bonds are formed when the attractions of the atoms for the pair of bonding electrons are different (they elements involved have different electronegativity values).

Question 3

What occurs when polar covalent bonds happen?

Answer 3

When this occurs, one atom will become delta positive (δ+ ) and the other delta negative (δ- ). The atom with the HIGHER electronegativity will be delta negative (δ- ) – this is because it is ‘pulling the electrons closer’

Question 4

Why are not all substances with polar covalent bonds, polar molecules?

Answer 4

Not all substances with polar covalent bonds will be polar molecules. This is because the spatial arrangement of the atoms has an effect - if the molecule has a symmetrical arrangement of polar and non-polar bonds, the overall polarity is cancelled out.

Question 5

How do you write an ionic formula?

Answer 5

The chemical formula for the compound:
Li2O

Lithium is a valency of 1 so has a charge of 1+, oxygen has a valency of 2 so has a charge of 2-. We know lithium is positive as it is a metal and oxygen is negative as it is a non-metal.

However, since there are 2 lithium atoms, we need to show this in the formula. It is done using brackets:
(Li+)2O2-

Question 6

Describe the bonding continuum?

Answer 6

The bonding continuum shows the ‘continuum’ of states from covalent to ionic bonds.

Question 7

what would happen to each of these processes at room temperature? Covalent network, covalent molecular, ionic substances

Answer 7

At room temperature:
Covalent networks - solid
Covalent molecular - gas or liquids
Ionic substances - solid
Melting point

Question 8

State the melting points of the following processes? Covalent molecular, covalent network, ionic bonds

Answer 8

Melting point
Covalent molecular - low melting points
Covalent network - high melting points
Ionic bonds - high melting points

Question 9

What is solubility?

Answer 9

Solubility – solubility decreases as molecules increase in size. Polar covalent compounds and ionic substances tend to be soluble in water. (Remember ‘like dissolves like’).

Question 10

What is electrical conductivity

Answer 10

Electrical conductivity – covalent bonds do not conduct (with the exception of carbon in the form of graphite), ionic bonds can conduct when molten or in solution (aq).

Question 11

What are intermolecular forces?

Answer 11

Intermolecular forces act between molecules. These are known as van der Waals (vdW) forces.
They are three different types of bonding within :London dispersion forces (LDFs), Permanent dipole-permanent dipole (Pd-Pd) forces and Hydrogen bonding

Question 12

Describe London dispersion forces (LDF)?

Answer 12

LDFs can operate between all atoms and molecules. They are formed by the electrostatic attraction between temporary dipoles and induced dipoles which are caused by the movement of electrons in atoms and molecules (electrons are continuously moving, why we get LDFs between all atoms and molecules, even monatomic atoms).

Question 13

Is LDF the weakest intermolecular force?

Answer 13

True

Question 14

What is a polar molecule?

Answer 14

Molecules are polar when they have a permanent dipole (one end of the molecule is permanently negative, other positive).

Question 15

What is permanent- dipole-permanent dipole interaction (Pd-Pd)?

Answer 15

Dipole-Dipole interaction is the attraction between oppositely charged ends of polar moelcules. They are stronger than LDFs

Question 16

Describe a hydrogen bond?

Answer 16

Hydrogen bonds are Pd-Pd interactions found between molecules which contain highly polar bonds and are also the strongest intermolecular force

They can form between:
Hydrogen – Nitrogen
Hydrogen – oxygen
Hydrogen – Fluorine
(NOF elements)

Question 17

What happens to the melting and boiling points, if hydrogen bonding is present?

Answer 17

When hydrogen bonds are present, melting and boiling points will be much higher than those other compounds of similar molecular size.

Question 18

How do intermolecular forces of attraction affect a molecules physical property?

Answer 18

The stronger the intermolecular force of attraction, the higher the melting and boiling point and increasing viscosity.

Question 19

Why does ammonia and water have high boiling points?

Answer 19

Ammonia and water have high boiling due to hydrogen bonding.

Question 20

How do you predict the solubility of a compound?

Answer 20

‘Like dissolves like’. This means that polar substances will be soluble in other polar solvents (so any polar substance tends to be soluble in water) and non-polar substances tend to be soluble in non-polar solvents.

Non-polar substances will not be miscible in water (the reason oil and water do not mix).