Topic 2 Structure And Bonding

Question 1

Define Ionic Bond:

Answer 1

Ionic bonding is the strong electrostatic attraction between oppositely charged ions.

Question 2

The effect that ionic radius has on strength of ionic bonding:

Answer 2

The smaller the ions, the more closely they can be packed together in the ionic lattice. The shorter the distance between oppositely charged ions, the stronger the electrostatic forces between them and hence the stronger the ionic bond.

Question 3

The effect that ionic charge has on the strength of ionic bonding:

Answer 3

the greater the charge on the ions involved, the stronger an ionic bond will be.

Question 4

Trends of ionic radii down a group:

Answer 4

Ionic radii increases due to the number of shells increasing

Question 5

Trends of ionic radii across a period:

Answer 5

As the elements continue across the period, the ionic radii decreases due to the increase of protons. This is because increasing the number of protons means more attraction between protons and electrons so the outer electrons are closer to the nucleus, so, ionic radii decreases.

Question 6

Physical properties of ionic compounds

Answer 6

• High melting point
• Brittleness
• They can conduct electricity
• Soluble

Question 7

Why do ionic compounds have high melting points?

Answer 7

When an ionic substance melts, the giant ionic lattice is broken. In its molten state, the ions are free to move around. To free the ions during melting, the ionic bonds must be broken. The ionic bonds are strong so lots of energy is required to break them, so, they have high melting points.

Question 8

Why are ionic compounds brittle?

Answer 8

If you move a layer of ions, you get ions of the same charge next to each other. The layers then repel each other and the crystal breaks up.

Question 9

How are ionic compounds conducive?

Answer 9

In a solid, the ions are fixed in a lattice and cannot move. In a molten or aqueous solution, ions can move and so can conduct electricity throughout the compound.

Question 10

How are ionic compounds soluble?

Answer 10

Ionic crystals are polar. Similar to water molecules as they are polar too. As oxygen atoms are slightly negatively charged and hydrogen atoms are slightly positively charged, the hydrogen atoms will surround the negative ions and the oxygen atoms will surround the positive ions. This is hydration which provides energy needed to separate the ions in the lattice. The the ionic compounds becomes a solution.

Question 11

Evidence for the existence and migration of ions:

Answer 11

Electrolysis of copper chromate shows this. Copper chromate is a dark green ionic solid. Passing an electric current through a copper chromate solution results in the migration of two coloured ions. Blue copper cations (2+) near the cathode. Yellow chromate (2-) anions near the anode.

Question 12

Define covalent bond:

Answer 12

A covalent bond is the strong electrostatic attraction between two nuclei and the shared pair of electrons between them.

Question 13

Define dative bond:

Answer 13

A dative bond is a type of covalent bond in which a pair of lone electrons from one atom are shared with another atom.

Question 14

Relationship between bond length and bond strength:

Answer 14

Generally, as the bond strength increases, the bond length decreases. Evidence is shown in triple, double and single bonds.

Question 15

How is the shape of a simple molecule or ion determined?

Answer 15

By the repulsion between the electron pairs that surround a central atom.

Question 16

Define electronegativity:

Answer 16

Electronegativity is the ability of an atom to attract a bonding pair of electrons in a covalent bond.

Question 17

What are covalent and ionic bonding the extremes of?

Answer 17

They are the extremes of a continuum of bonding type.

Question 18

What does a difference in electronegativity cause?

Answer 18

It causes bond polarity in bonds and molecules.

Question 19

Difference between polar bonds and polar molecules:

Answer 19

A polar bond is one where the charge distribution between the two atoms in the bond is unequal. A polar molecule is one where the charge distribution around the molecule is not symmetrical.

Question 20

how to predict if a molecule is polar?

Answer 20

If the difference in electronegativity for the atoms in a bond is greater than 0.4.

Question 21

Nature of intermolecular forces resulting from London forces (instantaneous dipole)

Answer 21

the weakest type of intermolecular bond. They exist between all atoms and molecules.

Question 22

Nature of intermolecular forces resulting from permanent dipoles

Answer 22

Permanent dipole-dipole forces are the weak intermolecular forces of attraction

Question 23

Nature of intermolecular forces resulting from hydrogen bonds:

Answer 23

Hydrogen bond is the strongest type of intermolecular bond. It’s a specific type of permanent dipole to permanent dipole attraction.

Question 24

Interactions in molecules which give rise to hydrogen bonds e.g. H20, liquid NH3, liquid HF etc.

Answer 24

A hydrogen bond is an intermolecular force that forms a special type of dipole-dipole attraction when a hydrogen atom bonded to a strongly electronegative atom exists in the vicinity of another electronegative atom with a lone pair of electrons. Intermolecular forces occur between molecules.

Question 25

Does water have a relatively high melting/boiling point, why?

Answer 25

Yes, water’s hydrogen bonds between water molecules can absorb a lot of energy so water has a high specific heat capacity - it takes a lot of energy to heat it up. This means water doesn’t experience rapid temperature changes.

Question 26

Why is ice’s density lower than water?

Answer 26

Water molecules are held further apart in ice than they are in liquid water because each water molecule forms four hydrogen bonds to another water molecule, making a lattice shape.

Question 27

Trends in boiling temperatures of alkanes with increasing chain length:

Answer 27

As the size of an alkane increases, its boiling/melting point increases (as well as its density and viscosity). This is because the intermolecular forces between larger alkane molecules are stronger than those between smaller molecules.

Question 28

Effect of branching in the carbon chain on the boiling temperatures of alkanes:

Answer 28

Branching of an alkane chain makes the molecules more compact and brings various atoms closer, decreasing molecular size. Since a sphere has minimal surface area, Van der Waal forces of attraction are minimum and hence the boiling point of the alkane decreases with branching.

Question 29

Why do alcohols have a relatively low volatility compared to alkanes with a similar number of electrons?

Answer 29

Alcohols are less volatile than alkanes due to alcohols having hydrogen bonds between the molecules whereas alkanes have weaker Van der Waal interactions.

Question 30

What are the trends in boiling points of the hydrogen halides, HF to HI?

Answer 30

HF has the highest boiling point followed by HI, then HBr with HCl having the lowest boiling points. This is because HF is able to form hydrogen bonds whereas the others are unable to do so as their electronegativity isn’t large enough to create a sufficient dipole.

Question 31

Factors that influence water to dissolve some ionic compounds, in terms of the hydration of the ions:

Answer 31

If the hydration energy of an ionic compound exceeds its lattice energy, the lattice is broken and the ions in the compound separate, causing the compound to dissolve. If the hydration energy of the compound is less than the lattice energy, the compound will not dissolve.

Question 32

Factors that influence water to dissolve simple alcohols:

Answer 32

Alcohols are compounds with a hydroxyl group and as a result can form hydrogen bonds with water.

Question 33

Factors that influence water to be a poor solvent for compounds:

Answer 33

Their dipole moment is too weak to form hydrogen bonds with water molecules. The hydrogen bonds between water molecules are stronger than the dipole interactions that can form between water molecules and the halogenoalkane so the compound doesn’t dissolve.

Question 34

Factors that influence non-aqueous solvents, for compounds that have similar intermolecular forces to those in the solvent.

Answer 34

Compounds which have similar intermolecular forces to those in the solvent will generally dissolve. Non-polar solutes will dissolve in non-polar solvents e.g. Iodine, which has only London forces between its molecules, will dissolve in a non-polar solvent such as hexane which also only has London forces.

Question 35

Define metallic bonding:

Answer 35

Metallic bonding the strong electrostatic attraction between metal anions and the delocalised electrons.

Question 36

Where are giant lattices present in?

Answer 36

• Ionic solids (Giant ionic lattices)
• Covalently bonded solids, such as diamond (giant covalent lattices)
• Solid metals (giant metallic lattices)

Question 37

Examples of simple molecular substances:

Answer 37

• ice (H20)
• iodine (I2)

Question 38

Different structures formed by carbon atoms:

Answer 38

• Graphite
• Graphene
• Diamond

Question 39

Properties of Graphite:

Answer 39

• 3 covalent bonds per atom in each layer
• Each carbon atom has one delocalised outer electron
• Can conduct electricity
• The layers in graphite can slide over each other because the forces are weak. Making graphite slippery, so it’s a useful lubricant

Question 40

Properties of Diamond:

Answer 40

• Giant covalent lattice
• Each carbon atom is joined to four other carbon atoms by covalent bonds
• The carbon atoms form a regular tetrahedral network
• No delocalised electrons
• Very hard

Question 41

Properties of graphene:

Answer 41

• Graphene is a single layer of graphite which is a sheet of carbon atoms covalently bonded forming a continuous hexagonal layer
• One atom thick
• Useful in fabricating composite materials and in electronics

Question 42

How does the types of particles present in an atom influence physical properties?

Answer 42

• Atoms: Pure metals consist of closely packed atoms held together by metallic bonds, resulting in good conductivity and varied (but mainly high boiling/melting points).
• Molecules: Simple molecular substances (H20, C02) consist of discrete molecules. They usually have lower melting points and boiling points due to weak intermolecular forces.
• Ions: Ionic compounds (NaCl) are composed of ions arranged in a lattice structure, leading to high melting/boiling points and the ability to conduct electricity when molten or dissolved in water.
  Electrons: In metals, delocalised electrons contribute to conductivity and malleability.

Question 43

How does the structure of the substance influence physical properties?

Answer 43

Crystal lattice: Ionic and metallic substances form regular structures that maximise attractive forces, leading to high melting/boiling points.
Molecular structure: Molecular structures have lower melting points due to the weak intermolecular forces between them.
Network structures: Covalent network solids (diamond, silicon dioxide) have strong bonds throughout resulting in very high melting/boiling points and typically low solubility in water.

Question 44

How does the type of bonding and intermolecular forces influence physical properties?

Answer 44

Ionic bonding: Strong electrostatic forces of attraction in ionic compounds lead to high melting/boiling points. They dissolve well in polar solvents like water and conduct electricity when dissolved or molten.
Covalent bonding: Compounds with covalent bonds (diamond) have high melting/boiling points while molecular compounds with weak intermolecular forces have low melting/boiling points.
Metallic bonding: Delocalised electrons allow for good conductivity and malleability, with melting points varying depending on the metal but they are usually higher.
Intermolecular forces: Hydrogen bonding (e.g. in water) results in higher boiling points compared to similar-sized molecules lacking such forces. Dipole-dipole interactions and van der walls forces also influence properties significantly.