2 Bonding, Structure and the Properties of Matter

Question 1

what is ionic bonding?

Answer 1

ionic bonding is the electrostatic attraction between positive and negative ions.
it is a relatively strong attraction.

Question 2

state properties of ionic substances.

Answer 2

• high melting and boiling points (strong electrostatic forces between oppositely charged ions).
• do not conduct electricity when solid (ions in fixed positions).
• conduct when molten or dissolved in water - ions are free to move.

Question 2

what is a covalent bond?

Answer 2

covalent bond is a shared pair of electrons between two atoms.

Question 2

how are ionic compounds held together?

Answer 2

• they are held together in a giant lattice.
• it’s a regular structure that extends in all directions in a substance.
• electrostatic attraction between positive and negative ions holds the structure together.

Question 3

give 5 examples of positive ions and 5 examples of negative ions (give names of negative anions). what is important when working out a formula of an ionic compound?

Answer 3

e.g. Positive: Na +, Mg 2+, Al 3+, Ca 2+, Rb +
e.g. Negative: Cl -, Br -, SO4 2-, NO3 -, OH - (chloride, bromide, sulfate, nitrate, hydroxide).
ionic compounds are electrically neutral, i.e. positive and negative charges balance each other.

Question 4

how are ionic compounds formed? explain in terms of MgO case.

Answer 4

reactions of a metal with a non-metal.
electron transfer occurs - metal gives away its outer shell electrons to non-metal.
Mg is in Group 2, so has 2 available outer shell electrons.
O is in Group 6, so can accept 2 electrons to get a full outer shell configuration.
Mg becomes Mg 2+ and O becomes O 2- (oxide).

Question 5

how do intermolecular forces change as the mass/size of the molecule increases?

Answer 5

they increase. that causes melting/boiling points to increase as well (more energy needed to overcome these forces).

Question 6

describe the structure and properties of simple molecular covalent substances.

Answer 6

• do not conduct electricity (no ions)
• small molecules
• weak intermolecular forces, therefore:
• low melting and boiling points

Question 7

what are polymers? what are thermosoftening polymers?

Answer 7

polymers are very large molecules (>100s, 1000s of atoms) with atoms linked by covalent bonds.
thermosoftening polymers - special type of polymers; they melt/soften when heated. there are no bonds between polymer chains. strong intermolecular forces ensure that the structure is solid at room temperature. these forces are overcome with heating - polymer melts.

Question 8

what are giant covalent substances? give examples.

Answer 8

• solids, atoms covalently bonded together in a giant lattice.
• high melting/boiling points - strong covalent bonds.
• mostly don’t conduct electricity (no delocalised e -)
• diamond, graphite, silicon dioxide.

Question 9

describe and explain the properties of allotropes of carbon.

Answer 9

diamond
- four, strong covalent bonds for each carbon atom
- very hard (strong bonds)
- very high melting point (strong bonds)
- does not conduct (no delocalised electrons)
graphite
- three covalent bonds for each carbon atom
- layers of hexagonal rings
- high melting point
- layers free to slide as weak intermolecular forces between layers; soft, can be used as a lubricant
- conduct thermal and electricity due to one delocalised electron per each carbon atom
fullerences
- hollow shaped molecules
- based on hexagonal rings but may have 5/7-carbon rings
- C60 has spherical shape, simple molecular structure (Buckminsterfullerene)
nanotubes
- cylindrical fullerene with high length to diameter ratio
- high tensile strength (strong bonds)
- conductivity (deloc, electrons)
graphene
- a single layer of graphite

Question 10

what are alloys? why are they harder than pure metals?

Answer 10

alloys:
- mixtures of metal with other elements, usually metals
- different sizes of atoms distorts the layers, so they can’t slide over each other, therefore alloys are harder than pure metals

Question 10

what is metallic bonding?

Answer 10

forces of attraction between delocalised electrons and nuclei of metal ions.

Question 11

describe properties of metals

Answer 11

• high melting/boiling points (strong forces of attraction)
• good conductors of heat and electricity (delocalised electrons)
• malleable, soft (layers of atoms can slide over each other whilst maintaining the attraction forces)

Question 12

what are the limitations of the simple model?

Answer 12

there are no forces between spheres and atoms, molecules and ions are solid spheres - this is not true

Question 13

what does the amount of energy needed to change state from solid to liquid or liquid to gas depend on?

Answer 13

the strength of the forces between the particles of the substance. the nature of the particles involved depends on the type of bonding and the structure of the substance. the stronger the forces between the particles the higher the melting point and boiling point of the substance.

Question 14

a pure substance will melt or boil at…?

Answer 14

a fixed temperature.
a mixture will melt over a range of temperatures.

Question 15

what is nanoscience?

Answer 15

science that studies particles that are 1-100nm in size.

Question 15

what are the three states of matter?

Answer 15

solid, liquid and gas.

Question 16

state the uses of nanoparticles.

Answer 16

• medicine (drug delivery systems)
• electronics
• deodorants
• sun creams (better skin coverage and more effective protection against cell damage)

Question 17

what are fine and coarse particles?

Answer 17

• fine particles (soot), 100-2500nm diameter
• coarse particles (dust), 2500-10^5nm diameter

Question 18

why do nanoparticles have properties different from those for the same materials in bulk?

Answer 18

high surface area to volume ratio.