AQA Chemistry GCSE (Topic 2: Bonding, Structure and the Properties of Matter) Flashcards
What is Ionic bonding?
Electrostatic attraction between positive and negative ions.
How are ionic compounds held together?
In a giant lattice, its a regular structure that extends in all directions in a substance, and electrostatic attraction between positive and negative ions hold the structure together.
State properties of ionic substances.
High melting and boilding 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.
What is important when working out a formula of an ionic compound?
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 Groiup VI, so can accept 2 electrons to get a full outer shell configuration.
Mg becomes Mg^2+ and O becomes O^2- (oxide).
What is a covalent bond?
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?
Polymers are very large molecules (>100s, 1000s of atoms) with atoms linked by covalent bonds.
What are thermosoftening polymers?
A special type of polymers; they melt/soften when heated. There are no bonds between polymer chains. Weak intermolecular forces ensure that the structure is solid at room temperature. These forces are overcme 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.
What is metallic bonding?
Forces of attraction between delocalised electrons and nuclei of metal ions.
Desribe properties of metals
High melting/boiling points (strong forces of attraction).
Good conductors of heat and electricity (delocalised electrons).
Malleable, soft (layers of atoms acn slide over each other whilst maintaining the attraction forces).
What are alloys?
Mixtures of metal with other elements, usually metals.
Why are alloys harder than pure metals?
Different sizes of atoms disorts the layers, so they can’t slide over each other, therefore alloys are harder than pure metals.
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. The 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…? What about the mixture?
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 stystems).
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 thoes for the same materials in bulk?
High surface area to volume ratio.
