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Infection and response
Organisation
Cell biology
Biological molecules
Homeostasis and response
Responding to change (a2 only)
Energy transfers (a2 only)
The control of gene expression (a-level only)
Substance exchange
Bioenergetics
Genetic information & variation
Inheritance, variation and evolution
Genetics & ecosystems (a2 only)
Ecology
Cells
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1f industrialisation and the people: britain, c1783-1885
1c the tudors: england, 1485-1603
Britain & the wider world: 1745 -1901
Inter-war germany
World war one
2n revolution and dictatorship: russia, 1917-1953
World war two & the holocaust
1l the quest for political stability: germany, 1871-1991
The cold war
2j america: a nation divided, c1845-1877
Medieval period: 1066 -1509
The fight for female suffrage
2m wars and welfare: britain in transition, 1906-1957
2d religious conflict and the church in england, c1529-c1570
Britain: 1509 -1745
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08/10/2023
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ionic compounds regular lattice structure 1) ionic compounds have a structure called an ionic lattice. 2) the ions form a closely packed regular lattice arrangement and there are very strong electrostatic forces of attraction between oppositely charged ions, in all directions. the ball and stick model shows the regular pattern of an ionic crystal and shows how all of the ions are arranged. it also suggests that the crystal extends beyond what shown in the diagram. the model isn't to scale though, so the relative sizes of the ions may not be shown. also, in reality, there aren't gaps between the ions. CI- Na+ this model shows the relative sizes of the ions, as well as the regular patterns of an ionic crystal, but it only lets you see the outer layer of the compound. the properties of ionic compounds 1) high melting and boiling points due to the strong bonds between the ions that take a lot of energy to overcome Made with Goodnotes 2) when they are solid, the ions are held in place so they can't conduct electricity. however when they melt, the ions are free to move and they'll carry an electric charge. 3) some ionic compounds dissolve in water. the ions separate and are all free to move in the solution, so they'll carry an electric charge. properties of simple molecular substances 1) the atoms within the molecules are...
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held together by very strong bonds. by contrast, the forces of attraction between these molecules are very weak. 2) low melting and boiling points due to weak intermolecular forces which don't take much energy to overcome 3) most molecular substances are gases or liquids at room temperature 4) as molecules get bigger, the strength of the intermolecular forces increase, more energy is needed to break them, and the melting and boiling points increase. 5) molecular substances don't conduct electricity, because they aren't charged so there are no free electrons or ions. giant covalent structures 1) in giant covalent structures, all the atoms are bonded to each other by strong covalent bonds. 2) they have very high melting and boiling points as lots of energy is needed to break the covalent bonds between the atoms. 3) they don't contain charged particles, so they don't conduct electricity - however, graphite does when molten because each carbon atom has one delocalised electron and can move. EXAMPLES: O each carbon atom forms 4 covalent bonds in a very rigid giant covalent structure. $8 each carbon atom forms three covalent bonds to create layers of hexagons, each carbon atom also has one delocalised electron. sometimes called silica, this is what sand is made of. each grain of sand is one giant structure of silicon and oxygen. polymers 1) in a polymer, lots of small units (monomers) are linked together to form a small molecule that has repeating sections. 2) all the atoms in a polymer are joined by covalent bonds. 3) most polymers are solid at room temperature because the intermolecular forces between polymer molecules are larger than between simple covalent molecules, so more energy is required to break them. 4) they generally have lower boiling points than ionic or giant molecular compounds becaused the intermolecular forces are weaker than ionic or covalent bonds.