Alevel Chemistry - Topic 2

Question 1

What is an ion?

Answer 1

A charged particle formed when an atom or group or atoms has lost, or gained, one or more electrons

Question 2

What are Cations?

Answer 2

Positively charged ions

Question 3

What are anions?

Answer 3

Negatively charged ions

Question 4

What is true about isoelectronic species?

Answer 4

Same number of electrons hence they have the same electronic configuration

Question 5

Which experiment provides evidence for ions?

Answer 5

Electrolysis provides evidence for ions because it represents the migration of ions either to the cathode (-) or the anode (+)

Question 6

What is ionic bonding?

Answer 6

Electrostatic forces of attraction between oppositely charged particles to form an ionic bond

Question 7

What is the trend of ionic radius down a group?

Answer 7

Increases

Question 8

What is, and explain, the trend of ionic radius across isoelectronic ions?

Answer 8

• As the atomic number increases
• The effective nuclear charge increase since all species have same number of electrons
• The attraction between their nucleus and electrons increase
• The ionic radius decreases

Question 9

What is charge density and how does this affect the bond?

Answer 9

Charge density is a measure of the charge/size ratio. Ions with a high charge density form stronger bonds than those with a low charge density

Question 10

What factors affect the strength of an ionic bond?

Answer 10

Strength increases when:
- There is an increase in ionic charge
- Decrease in ionic radius

Charge density has to be high*

Question 11

Why might the ionic bond between F- and Mg2+ be stronger than that if it was Li+

Answer 11

The sizes of lithium and magnesium ions are similar but magnesium ions have a higher charge. This means that magnesium ions have a higher charge density and are more strongly attracted to the Fluoride ions.

Question 12

What is a covalent bond?

Answer 12

The strong electrostatic forces of attraction between two nuclei and the shared pair of electrons between them

Question 13

Draw the two structures of sigma bonds?

Answer 13

The end on overlap between p or s orbitals.

Question 14

What the structure of a Pie bond or otherwise known as the double bond?

Answer 14

Sideways overlap of P orbitals

Question 15

What is a dative covalent bond?

Answer 15

When an orbital with a lone pair of electron in one atom overlaps with a vacant orbital in another atom

Question 16

What must be shown when drawing a dative convent bond dot-cross?

Answer 16

• Represented by an arrow from the atom providing the electron pair towards the atom with the vacant orbital
• If present, charge brackets must be shown to show polytomic ions
• Dots and crosses must be correctly shown, where two dots or crosses must be present in the same dative bond to show its coming from a single atom

Question 17

What is bond length?

Answer 17

The distance between the nuclei of two atoms that are covalently bonded together.

Question 18

How is bond strength measured?

Answer 18

Given by the bond enthaply for a particular covalent bond but note this changes with the environment a molecule is in.

Question 19

What is bond enthalpy?

Answer 19

The enthaply change when pone maple of a bond in gaseous state is broken in Kj/mol

Question 20

Explain the trend in bond strength of halogens? And what’s the exception?

Answer 20

• Down the group, the bond strength decreases.
• This is because the bond length increases
• so the halogen-halogen bond becomes weaker

*The exception to this is Florine since it is weaker than chlorine but has a shorter bond length. This is because its lone pairs of electrons are lose enough to produce a lot of repulsion

Question 21

Explain the trend between strength of C triple bond, C double bond, and C single bond?

Answer 21

• As the number of bonds decreases, the bond length increases
• This causes the the bond strength to decrease since the electrostatic attraction between the two nuclei and the shared electrons is decreased

Question 22

What dictates the shape of a molecule?

Answer 22

• The arrangement of electron pairs around the central atom keeps repulsion to a minimum

Question 23

From a tetrahedral shape, how much is the angle reduced by when a lone pair is added?

Answer 23

109.5 - y2.5

Question 24

Draw the structures:
- Linear
- trigonal planar
- Tetrahedral
- trigonal pyramidal
- trigonal bipyramidal
- Octahedral
- V shaped

Answer 24

• 180
• 120
• 109.5
• 107
• 90/120
• 90
• 104.5

Question 25

How do we draw 3d molecules?

Answer 25

Dashed line represents away (Into the plane of the paper)
Solid wedge represents towards (Coming out of the plane of the paper)
Solid line (In the plane of the paper)

Question 26

What is electronegativity?

Answer 26

The ability of an atom to attract the bonding electrons in a colvalent bond

Question 27

What is the trend in electronegativity?

Answer 27

Increase up a group, and across a period

Question 28

What is the most electronegative element?

Answer 28

Fluorine, based on the Pauling electronegativity scale

Question 29

What forms a polar covalent bond?

Answer 29

The bond is polar when the two bonded atoms have different electronegativity. However if a molecule is symmetrical, there will be no overall polarity because two identical dipoles cancel each other out; There may be polar bonds but it is not a polar molecule

Question 30

What can polar bonds be described as?

Answer 30

Colvalent bonds with a degree of ionic character

Question 31

In what sort of species can London dispersion forces exist in?

Answer 31

Non polar molecules

Question 32

What affects the strength of London forces?

Answer 32

• The number of electrons within the molecule (More electrons = More strength)
• Number of points of contact between molecules ( Great surface area = More strength)

Question 33

Apart from London dispersion forces, which other intermolecular forces can exist between molecules?

Answer 33

Permanent dipoles, and hydrogen bonding.

Question 34

What are the conditions for hydrogen bonding?

Answer 34

• Compound must contain hydrogen
• Hydrogen must be covalently bonded to to an atom of N, O, or F
• There must be a lone pair present on the N, O, or F

Question 35

Draw the bonding of two water molecules?

Answer 35

• 180 and straight towards the lone pair

Question 36

How does does water molecules form ice in terms of its structure

Answer 36

Each water molecule can form two hydrogen bonds on average, to forms open rings of six water molecules joined by hydrogen bonds.

Question 37

When can a solute be seen as soluble in a solvent?

Answer 37

Solution formed is clear, and can be colored or colorless

Question 38

What are the three conditions for a substance to dissolve?

Answer 38

• The solute particles can be separated from one another
• The separated solute particles can be surrounded by solvent particles
• The solute-solvent forces are greater than the solute-solute and solvent-solvent forces

Question 39

Explain in terms of the condition needed for soluble, why longer chains of alcohols become less soluble in water?

Answer 39

As the number of carbon atoms in an alcohol molecule increases, the London forces become stronger and more important. This may be less energy favorable for water molecules to break their hydrogen bonds to form hydrogen bonds with alcohols molecules, and therefore it becomes less soluble