bonding, structur and the properties of matter

Question 1

what is ionic bonding

Answer 1

inonic bonding is the electrostatic attraction between positive and negative ions

Question 2

how are ionic compounds held together

Answer 2

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

Question 3

state the properties of ionic substances

Answer 3

• hight melting and boiling point (strong electrostatic force bewteen oppositlet charged ions)
• do nto conduct electricity when solids (Ions in fixed positions)
• Conduct when molten or dissolved in water - ions are free to move

Question 4

give 5 examples of positive ions and 5 examples of negatie ions

Answer 4

positive - Na, Mg, Al, Ca, Rb
negative - Cl, Br, SO, NO, OH

Question 5

how are ionic compounds formed? Explain in terms of MgO case

Answer 5

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

Question 6

whtat is a convelent bond?

Answer 6

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

Question 7

describe the structure and properties of simple molecular convalent substances

Answer 7

• Do not conduct electricity (no ions)
• Small molecules
• Weak intermolecular forces, therefore:
• Low melting and boiling points

Question 8

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

Answer 8

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

Question 9

what are polymers? What are thermosoftening polymers?

Answer 9

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 10

what is a giant covalent substances? Give examples

Answer 10

• 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 11

Describe and explain the properties of allotropes of carbon

Answer 11

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 Fullerenes– hollow shaped molecules – based on hexagonal rings but may have 5/7-carbon rings– C 60has 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 12

what si metallic bonding

Answer 12

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

Question 13

describe properties of metals

Answer 13

• 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 14

what are alloys> Why are they harder than pure metals

Answer 14

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 15

what are the limitations of the simple model

Answer 15

There are no forces between spheres and atoms, molecules and ions are solid spheres – this is not true

Question 16

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

Answer 16

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 17

A pure substance will melt or boil at…? What about the mixture?

Answer 17

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

Question 18

What are the three states of matter?

Answer 18

Solid, liquid and gas

Question 19

What is nanoscience?

Answer 19

Science that studies particles that are 1 - 100nm in size

Question 20

State the uses of nanoparticles

Answer 20

• Medicine (drug delivery systems) - Electronics - Deodorants - Sun creams (better skin coverage and more effective protection against cell damage)

Question 21

What are fine and coarse particles?

Answer 21

• Fine particles (soot), 100-2500 nm diameter - Coarse particles (dust), 2500-10 5nm diameter

Question 22

Why do nanoparticles have different properties to those for the same materials in bulk?

Answer 22

High surface area to volume ratio