Topic 2 bonding structure and the properties of matter Flashcards
What is ionic bonding
Ionic bonding is the electrostatic 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 formula of an ionic compound?
E.g. Positive: Na+, Mg2+, Al3+, Ca2+, 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.
How are ionic compounds formed? Explain in terms of MgO case.
Reaction of 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 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 point to increase as well (more energy needed to overcome these forces ).
What are polymers? What are thermoseftening 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. Theses 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 point - strong covalent bonds.
- Mostly don’t conduct electricity (no delocalised e-)
- Diamond, graphite, silicon dioxide.
Describe and explain the properties of allotropes of carbon
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
- layer of hexagonal rings
- high melting point
- layers free to slide can be used as a lubricant
- conduct thermal and electricity due to one delocalised electron per each carbon atom
Fullerenes
- hallow 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 (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
What are the properties of a Simple Covalent bond?
Boiling points.
Low boiling points and melting points
- Because of weak intermolecular forces between molecules
Conductivity when solid
- Poor: no ions to conduct
Conductivity when molten
- Poor: no ions
General description
- Mostly gases and liquids
What are the properties of a Ionic bond?
Boiling points.
- High because of giant lattice of ions with strong forces between oppositely charged ions.
Conductivity when solid
- Poor: Ions can’t move
Conductivity when molten
- good: ions are free to move
General description
- Crystalline solids
What are the properties of a Giant covalent bond?
Boiling points.
High
- because of many strong covalent bonds between atoms in giant structure
Conductivity when solid
diamond and sand: poor, because electrons can’t move
graphite: good as free delocalised electrons between layers can move through structure
Conductivity when molten
- Poor
General description
- Solids
What are the properties of a Metallic bonds?
Boiling points.
high
Strong electrostatic forces between positive ions and delocalised electrons
Conductivity when solid
- Good: delocalised electrons are free to move through structure
Conductivity when molten
- Good
General description
- 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 no true
What does the amount of the 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. The stronger the sources 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 to volume ratio
