Unit 1 Section 4 Bonding

Question 0

What holds ionic compounds together?

Answer 0

The electrostatic attractions between cations and anions.

Question 1

What are the properties of ionic compounds?

Answer 1

They have high melting points meaning strong forces of attraction between ions.
Soluble in water but not in non-polar solvents. They have to be charged to be pulled apart by the time polar water.
Ionic compounds only conducts electricity when molten or dissolved as this is the only time ions can move.

Question 2

Why is the ionic radius greater than that of the atomic radius in metals?

Answer 2

The metal loses an electron so the positive charge of nucleus is greater than that of the electron cloud, meaning the electrons are drawn closer.
Also sometimes they lose an electron shell, meaning less electron shielding.

Question 3

Why in non metals is the ionic radius greater than that of the atomic radius?

Answer 3

It will gain electrons. These means a more negative electron cloud that will repel its self meaning it will expand.

Question 4

What is the trend with ionic radiuses down a group?

Answer 4

It goes up due to the extra electron shells

Question 5

How is an ionic bond shown in an electron density map?

Answer 5

There will be a gap between the 2 ions showing no electron density.

Question 6

What are Born-Haber cycles usually used for?

Answer 6

Calculating lattice energy (the energy change when gaseous ions form 1 mole of an ionic solid understand conditions.
It can be found if you know the standard enthalpy of formation as one of the routes and all the other things with lattice energy as the other.

Question 7

If a compound produced a lot of energy when being formed, what does this imply about the stability?

Answer 7

It is very stable.

Question 8

Why doesn’t NaCl₂ exist?

Answer 8

To make is Na²⁺ would be needed which means second ionisation energies meaning lots of energy is put into it. Forming it is endothermic so it is energetically unfavourable.

Question 9

Why doesn’t MgCl form?

Answer 9

The formation is exothermic but it does contain a lot of energy. When ever it does form it disproportionates to MgCl₂ and Mg

Question 10

When a theoretical lattice energy is compared to that of the experimental one, what does it tell you about the structure of the compound?

Answer 10

If the 2 are very similar, then it is a very ionic compound. If not, then is suggests that the electron clouds have been distorted meaning it has become slightly covalent meaning the experimental enthalpy is more negative.

Question 11

What affects how polarising an ion is?

Answer 11

Small cations with a large charge are very polarising as they have a larger charge density.

Question 12

What determines how easily an anion is polarised?

Answer 12

The larger it is the easier it is to be polarised as ther electrons are further away from the nucleus.

Question 13

When 2 s orbitals over lapp, what type of bond is it?

Answer 13

A sigma bond.

Question 14

What happens when electrons in P orbitals overlap?

Answer 14

A pi bond is formed.

Question 15

Why is the pi bond less strong then the sigma bond?

Answer 15

It is less tightly bound the the two nuclei meaning it is weaker and more reactive.
They are parallel and so have less of an overlay with the P orbitals meaning they are weaker.

Question 16

What is dative covalent bonding?

Answer 16

It occurs when both the electrons come from the same atom. It occurs in the NH₄⁺ ion where a nitrogen will donate 2 electrons to a positive hydrogen which won’t have any electrons.

Question 17

Explain the metallic properties with reference to the metallic bonding.

Answer 17

High melting points. The more electrons the greater the bond strength and the greater the boiling point.
The size affects boiling point. The smaller the ions the greater the charge density and the greater the boiling point.
They are malleable and ductile.
The delocalised electrons carry charge and heat.
Insoluble.

Question 18

What is some evidence for the existence of ions?

Answer 18

Physical properties of ionic compounds: high melting
temperatures, showing strong forces of attraction between
ions, soluble in polar solvents, conduct electricity when
molten or in aqueous solution.
• Electron density maps of compounds produced from X-ray
diffraction patterns show zero electron density between ions
– meaning complete electron transfer.
• Migration of ions in electrolysis. For example, electrolysis of
green aqueous copper(II) chromate(VI) attracts a yellow colour
(chromate(VI) ions) to the anode and a blue colour (copper(II)
ions) to the cathode.

Question 19

Define first ionization energy

Answer 19

The first ionisation enthalpy is the enthalpy change
required to remove 1 mole of electrons from 1 mole
of gaseous atoms to form 1 mole of gaseous ions
with a +1 charge

Question 20

What is the first electron affinity?

Answer 20

The first electron affinity is the enthalpy change that
occurs when 1 mole of gaseous atoms gain 1 mole of
electrons to form 1 mole of gaseous ions with a –1
charge

Question 21

Why is first electron affinity exothermic?

Answer 21

The nucleus attracts the electron to it.

Question 22

Why is the second electron affinity exothermic?

Answer 22

It is repelled by the negative ion.

Question 23

What is the enthaply of lattice formation?

Answer 23

The standard enthalpy change when 1 mole

of an ionic crystal lattice is formed from its constituent ions in gaseous form.

Question 24

What affects the size of metallic bonds?

Answer 24

1. Number of protons/ Strength of nuclear attraction.
   The more protons the stronger the bond
2. Number of delocalised electrons per atom (the outer shell electrons are delocalised)
   The more delocalised electrons the stronger the bond
3. Size of ion.
   The smaller the ion, the stronger the bond

Question 25

Do metals conduct electricity in solution?

Answer 25

Yes as there are still delocalised electrons.

Question 26

what is the structure and bonding of sodium?

Answer 26

giant and metallic

Question 27

what is the structure and bonding of silicon?

Answer 27

giant (molecular) and covalent

Question 28

what is the structure and bonding of sulphur?

Answer 28

simple molecular and van der waals/ covalent