Bonding, Structure & Properties of Matter Flashcards
What is ionic bonding?
Ionic bonding is there electristatic attraction between positive and negative ions.
It is a relatively strong attraction
How are ionic compounds held together?
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
State properties of ionic substances
High melting and boiling point (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
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?
E.g. Positive: Na+, Mg2+, Al3+, Ca2+, Rb+
E.g. Negative: Cl-, Br-, SO₄²⁻, NO⁻ ₃, OH- (chloride, bromide, sulfate, nitrate, hydroxide).
Ionic compounds are electrically neutral, i.e. positive and negative charges balance each other
How are ionic compounds formed? Explain in terms of MgO case.
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 Mg2+ and O becomes O2- (oxide)
What is a covalent bond?
Covalent bond is a shared pair of electrons between two atoms
Describe the structure and properties of simple molecular covalent substances
Do not conduct electricity (no ions)
Small molecules
Weak intermolecular forces, therefore:
Low melting and boiling points
How do intermolecular forces change as the mass/size of the molecule increases?
They increase. That causes melting/boiling points to increase as well (more energy needed to overcome these forces)
What are polymers? What are thermosoftening polymers?
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.
What are giant covalent substances? Give examples
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
Describe and explain the properties of 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)
Describe and explain the properties of graphite
- three covalent bonds for each carbon atom
- laters of hexagonal rings
- high melting point
- laters 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
Describe and explain the porperties of fullerenes
- hollow shaped molecules
- based on hexagonal rings but may have 5/7-carbon rings
- C60 has spherical shape, simple molecular structure (buckminsterfullerene)
Describe and explain the properties of nanotubes and graphene
Nanotubes:
- cylindrical fullerene with high length to diameter ratio
- high tensile strength (strong bonds)
- conductivity (delocalised electrons)
Graphene - a single layer of graphite
what is metallic bonding?
forces of attraction between delocalised electrons and nuclei of metal ions
Describe properties of metals
- 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)
What are alloys? Why are they harder than pure metals?
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
describe the melting and boiling points of simple covalent bonds
low - because of weak intermolecular forces between molecules
describe the melting and boiling points of ionic bonds
high - because of giant lattice of ions with strong forces between oppositely charged ions
describe the melting and boiling points of giant covalent bonds
high - because of many strong covalent bonds between atoms in giant structure
describe the melting and boiling points of metallic bonds
high - strong electrostatic forces between positive ions and delocalised electrons
what is the conductivity when solid of simple covalent bonds
poor: no ions to conduct
what is the conductivity when solid of ionic bonds
poor: ions can’t move
what is the conductivity when solid of giant covalent bonds
diamond and sand: poor, because electrons can’tmove
graphite: good as free delocalised electrons between layers can move through structure
what is the conductivity when solid of metallic bonds
good: delocalised electrons are free to move through structure
what is the conductivity when molten of simple covalent bonds
poor: no ions
what is the conductivity when molten of ionic bonds
good: ions are free to move
what is the conductivity when molten of giant covalent bonds
poor
what is the conductivity when molten of metallic bonds
good
what is the general description of simple covalent bonds
mostly gases and liquids
what is the general description of ionic bonds
crystalline solids
what is the general description of giant covalent bonds
solids
what is the general description of metallic bonds
shiny metal solids
what are the limitations of the simple model?
There are no forces between spheres and atoms, molecules and ions are solid spheres - this is not true
What does the amount of energy needed to change state from solid to liquid or liquid to gas depend on?
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. Ther stronger the forces between the particles the higher the melting point and boiling point of the substance
A pure substance will melt or boil at…?
A fixed temperature.
A mixture will melt over a range of temperatures
What are the three states of matter?
solid, liquid and gas
What is nanoscience?
Science that studies particles that are 1 - 100nm in size
State the uses of nanoparticles
- medicine (drug delivery systems)
- electronics
- deodorants
- sun creams (better skin coverage and more effective protection against cell damage)
What are fine and coarse particles?
- Fine particles (soot), 100-2500 nm diameter
- coarse particles (dust), 2500-10^5 nm diameter
Why do nanoparticles have properties different from those for the same materials in bulk?
high surface area to volume ratio
