Week 5: Bonding

Question 1

Why do atoms react?

Answer 1

To gain a full outer shell.

Question 2

What do ionic compounds often exist (as in the solid state)?

Answer 2

Giant crystalline lattices with alternating cations and anions, held together by the attraction of their opposite charges.

Question 3

What are the properties of Ionic Compounds?

Answer 3

• High melting points
• Often water soluble
• Conduct electricity when liquid or in the aqueous solution.
• Crystals shatter easily

Question 4

Why do ionic compounds have high melting/boiling points?

Answer 4

Held together by strong electrostatic forces.

Question 5

What causes electrical conductivity?

Answer 5

The movement of charged particles, such as ions.

Question 6

Why can ionic compounds conduct electricity when melted?

Answer 6

The ions are fused are free to move about.

Question 7

How can ionic compounds conduct electricity in an aqueous solution?

Answer 7

The layers of water molecules reduce the attractions of positive and negative ions, meaning that the kinetic energy of the ions is enough for them to move freely.
- Ions will then move towards charged electrodes.

Question 8

What does it mean if ions are hydrated?

Answer 8

Soluble ionic lattices dissolve when placed into water.
The ions become surrounded by water molecules and are said to be hydrated.

Question 9

Why are ions and water attracted to eachother?

Answer 9

As water is a polar molecule

Question 10

Why is water a polar molecule?

Answer 10

H and O2 are share electrons but the oxygen has a greater attraction for the shared electrons.
This makes the oxygen slightly more negative.

Question 11

What is electronegativity?

Answer 11

A value which shows how much an element holds onto its electrons.

Question 12

Which factor influences electronegativity?

Answer 12

Nuclear charge
(Shown by electronegativity increasing along rows)

Question 13

What is a Covalent bond?

Answer 13

A bond involving shared electrons.
Involves non-metals.

Question 14

How does electronegativity influence covalent bonds?

Answer 14

Occurs with elements that have almost identical electronegativities.

Question 15

What is a dipole?

Answer 15

Bond/Molecule with ends that have opposite charges.

Question 16

Are polar covalent molecules soluble in water?

Answer 16

Yes

Question 17

Are non-polar molecules soluble in water?

Answer 17

No

Question 18

What are Van-der-Waals forces?

Answer 18

• As an atom moves its electrons are moving meaning there will be points when the nucleus of the atom is not directly at the centre.
• This means that the side furthest away from the nucleus will be more negative due to the electron cloud being more on one side than the other.
• This forms a temporary dipole.
• This may induce a dipole in another atom, making it an induced dipole.
• Induced-dipole-Induced-dipole interactions are called Van der Waals forces.

Question 19

What increases Van der Waals forces?

Answer 19

Molecular size due to larger electron clouds

Question 20

Is a a water-insoluble molecule hydrophilic or hydrophobic?

Answer 20

Hydrophobic

Question 21

How does as a water-insoluble molecule interact when places in water?

Answer 21

Hydrophobic - So they will clump together in order to minimise disruption to the H-bonding network in water.

Question 22

How does Hydrogen bonding occur?

Answer 22

Interaction between a hydrogen attached to an electronegative element and an atom with a lone pair of electrons.

Question 23

How do hydrogen bonds hold other elements together?

Answer 23

• When a hydrogen atom is covalently bonded to a very electronegative element (such as fluorine or oxygen), the polarity enables different molecules to attract each other.
• These forces are in addition to the van der Waals forces already present.
• The hydrogen atoms act as a bridge between atoms of the other element.
• The links between the hydrogen atoms and the electro negative atoms are called hydrogen bonds.

Question 24

Order the three bonds in terms of strength?

Answer 24

Covalent
Van der Waals
Hydrogen

Question 25

Which bonds continuously break and form in the liquid state?

Answer 25

Hydrogen bonds and van der Waals forces

Question 26

When sigma bonds form (such as carbon in methane), how do they move?

Answer 26

The sigma bonds move as far apart as possible.
This is because of the repulsion between these regions of high electron density.

Question 27

What does a thick-wedge bond represent?

Answer 27

Bond is coming out of the page

Question 28

What does a dashed bond represent?

Answer 28

Bond is going into the page