Structure 2.1-2.3

Question 1

Why do ionic compounds form crystals?

Answer 1

Bond to form a regular, repeating 3-dimensional shape

Question 2

Properties of an ionic compound

Answer 2

• Crystalline structure at room temperature and pressure
• Low volatility, high melting and boiling points
• Conducts electricity when molten or aqueous
• Hard but brittle

Question 3

Why do ionic compounds form lattice/ crystalline structures?

Answer 3

they form a regular repeating 3d arrangement of cations and anions- ionic lattice

Question 4

What can affect the shape of the lattice structure

Answer 4

• Ionic radii (greater radii= weaker bonding)
• Charge of ions (greater charge= stronger bonding)

Question 5

Why do ionic compounds have low volatilities and high melting and boiling points?

Answer 5

Strong electrostatic attraction between ions of opposite charge means large amounts of thermal energy are required to separate such ions.

Question 6

What is an ionic bond

Answer 6

The strong electrostatic attraction between cations and anions

Question 7

What is lattice enthalpy?

Answer 7

The energy needed to separate one mole of a solid ionic compound into gaseous ions under standard conditions

Question 8

Why do ionic compounds conduct electricity when molten or aqueous?

Answer 8

For a substance to conduct electricity, it must possess:
1. free moving
2. charged particles
- When it is solid, ions are held rigidly in place in the lattice- unable to move
- When the compound is molten or aqueous, the ions are free to move towards electrodes of opposite charges

Question 9

What effects lattice enthalpy?

Answer 9

• Charge of ions- stronger electrostatic attraction means more energy required to break, higher lattice enthalpy
• Ionic radii- larger radii means more separation of charges, weaker electrostatic attraction, lower lattice enthalpy

Question 10

Solubility of ionic compounds

Question 11

why are ionic compounds hard but brittle?

Answer 11

Hard- ions are held rigidly in place due to the strong electrostatic attraction between cations and anions
Brittle- if sufficient force is applied, rows of ions will move relative to one another, ions of like charges will become adjacent and repel, causing the lattice to shatter.

Question 12

Properties of a covalent compound

Answer 12

• Can be elements or compounds
• Can be solids, liquids or gases at room temperature
• Can have low melting and boiling points
• Are generally poor conductors of heat and electricity

Question 13

Optimal bond length of covalent bond

Question 14

Types of covalent bonds

Answer 14

Covalent bonds can form between:
* A small number of atoms to form small (discrete) molecules.
* A large number of atoms to form large molecules such as polymers, plastics and fullerenes.
* An infinite number of atoms to form covalent networks such as graphite, graphene, diamond, silicon and silicon
dioxide.

Question 15

What is an octet and a doublet

Answer 15

Octet= 8 electrons in outer shell (rocking a p6)
Doublet= helium

Question 16

Steps of drawing a lewis formula

Answer 16

Drawing Lewis formulas of molecules and ions
1. Add up the total number of valence electrons available in the molecule.
For a polyatomic ion, add additional electrons if negatively charged, or subtract electrons if positively charged.
2. Write atoms in the order they are bonded to one another, and place single covalent bonds between them.
In small molecules, the non-metal atom which forms the most bonds (and has the lower electronegativity) is
usually the central atom.
3. Add non-bonding electrons to the non-central atoms such that each has an octet of electrons.
4. Place any remaining electrons on the central atom.
5. If there aren’t enough electrons to give the central atom an octet, use pair(s) of non-bonding electrons on the
non-central atoms to form double/triple bonds.
6. If a polyatomic ion, draw square brackets around the Lewis formula and write the overall charge outside the
brackets at the top right corner

Question 17

Relationship betweem bond strength and number of shared electrons

Answer 17

As number of shared electrons increases, bond strength increases

Question 18

Relationship betweem bond length and number of shared electrons

Answer 18

As number of shared electrons increases, bond length decreases

Question 19

What is a coordinate covalent bond?

Answer 19

A covalent bond in which both of the shared pair of electrons originate from the same atom

Question 20

What are the 3 electron domain geometries?

Answer 20

i. linear
ii. trigonal planar
iii. tetrahedral

Question 21

What are the types of molecular geometry (shape of the molecule) and their bond angles?

Answer 21

i. linear (180)
ii. v-shaped / bent (tetrahedral= 105, trigonal planar= 116)
iii. trigonal planar (120)
iv. trigonal pyramidal (107)
v. tetrahedral (109.5)

Question 22

Metallic bonding model

Answer 22

valence electrons become DELOCALISED.
* the resulting metal cations are densely packed in a regular, repeating, 3-dimensional arrangement.
* the delocalised valence electrons spread themselves throughout the metallic lattice and are referred to as
the sea of delocalised electrons

Question 23

What is metallic bonding?

Answer 23

The electrostatic attraction between the lattice of cations and the sea of delocalised electrons

Question 24

Properties of metals

Answer 24

• Lustrous
• Dense
• Malleable and ductile
• Good conductors of heat and electricity
• High boiling point (and often high melting point)

Question 25

Why are metals good conductors of electricity when solid and molten?

Answer 25

For a substance to conduct electricity it must contain:
- freely moving
- charged particles (electrons and/or ions)
Delocalised electrons are FREE TO MOVE, therefore can conduct electricity flow from negative to positive terminals

Question 26

Why are metals good conductors of heat?

Answer 26

When heated, the kinetic energy of delocalised electrons is increased and rapidly distributed through the lattice.
Increased lattice vibrations also pass energy on from one densely packed metal cation to the next

Question 27

Why are metals malleable and ductile?

Answer 27

Layers of cations can be forced across each other. The delocalised electrons move to compensate for this and reestablish the electrostatic forces of attraction.

Question 28

Why do metals have high boiling points, and often high melting points?

Answer 28

Large amounts of heat energy are required to overcome the strong electrostatic forces of attraction between the
cations and the delocalised electrons

Question 29

Why do metals generally have high densities?

Answer 29

The ions in the lattice are closely packed and thus have a high mass per unit volume

Question 30

Why are metals lustrous?

Answer 30

Delocalised electrons reflect light

Question 31

What is charge density?

Answer 31

The ratio of ion charge to the volume of the ion

Question 32

What is an alloy?

Answer 32

A mixture of a metal with one or more other elements, such that the mixture still retains the physical properties of a metal.

Question 33

What physical properties of a metal may be altered by alloying?

Answer 33

Hardness/ malleability
and melting temperature

Question 34

What are the ways of categorising alloys?

Answer 34

• Substitutional alloy (atoms of similar size)
• Interstitial alloy (atoms of different sizes)
• Homogeneous alloy (atoms of different elements distributed uniformly)
• Heterogeneous alloy (contains crystalline phases with different compositions)

Question 35

Substitutional alloys

Answer 35

Where one metal cation is swapped for another with a similar ionic radii. As the ions have slightly different radii, the layers within the lattice are restricted in their movement relative to each other, creating a harder, less malleable metal.