Topic 1 - types of substances

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15 Terms

1
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1.32 Explain why elements and compounds can be classified as: a) ionic

- Ionic compounds are made of a metal and non metal

- They have regular structures (giant ionic lattices) in which there are strong electrostatic forces of attraction in all directions between oppositely charged ions

- They have high mpt and bpt as there are many strong bonds that require lots of energy to overcome

- They conduct electricity when molten or aqueous but not solid as ions need to be able to move and carry charge

- Often dissolve in water to form an aqueous solution

2
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1.32 Explain why elements and compounds can be classified as: b) simple molecular (covalent)

- Substances that consist of small molecules are usually gases or liquids that have low boiling and melting points, they are made of non-metal elements

- They have weak intermolecular forces between molecules, these are broken when melted or boiled, not the covalent bonds

- The intermolecular forces increase with the size of the molecules, so larger molecules have higher melting point and boiling point

- They don't conduct electricity, because ions aren't free to move or carry charge

- Many are insoluble but some are soluble because they can form intermolecular forces with water which are stronger than those between the water molecules or their own molecules already (eg. CO2 and NH3 are soluble)

3
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1.32 Explain why elements and compounds can be classified as: c) giant covalent

- Made up of non-metal elements

- Very high melting point as all of the atoms are linked to other atoms by strong covalent bondsterm-1 and these bonds must be overcome to boil or melt the substance

- Cannot conduct as ions aren't free to move or carry charge

4
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1.32 Explain why elements and compounds can be classified as: d) metallic

- Metals consist of giant structures of atoms arranged in a regular pattern

- They are always made up of just metallic elements

- The electrons in the outer shell of metal atoms are delocalised and so are free to move through the whole structure

- The sharing of delocalised electrons gives rise to strong metallic bonds

- High mpt and bpt

- Can conduct heat and electricity as delocalised electrons can move and carry charge

- Malleable as atoms can slide over each other

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1.33 Explain the properties of ionic compounds limited to: a high melting points and boiling points, in terms of forces between ions, b whether or not they conduct electricity as solids, when molten and in aqueous solution

High melting and boiling points - strong electrostatic forces

Conduct electricity when molten/ dissolved - ions can move

Don't conduct electricity when solid - ions are fixed in place

6
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1.34 Explain the properties of typical covalent, simple molecular compounds limited to:a low melting points and boiling points, in terms of forces between molecules (intermolecular forces), b poor conduction of electricity

- Low melting and and boiling points, only weak forces between molecules must be overcome, not covalent bonds

- Poor conduction of electricity - no charged particles or electrons that are free to move

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1.35: What are graphite and diamond?

Graphite and diamond are different forms of carbon and that they are examples of giant covalent substances

8
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describe the structure of graphite

Graphite: Each carbon is covalently bonded to three others, forming layers of hexagonal rings, which have no covalent bonds between layers, the layers can slide over each other because of this but there are weak intermolecular forces. Makes graphite soft and slippery. One electron from each carbon is delocalised as it is not held in the covalent bond, similar to metals, can conduct electricity unlike diamond.

high m/p

9
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describe the structure of diamond

diamon has 4 covalent bond for each atom

it is hard because of its rigid network of carbom atoms in the tetrahedal arrangement

poor conductor of electricity as it has no free charged particles

High m/p

10
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1.37 Explain, in terms of structure and bonding, why graphite is used to make electrodes and as a lubricant, whereas diamond is used in cutting tools

Graphite is used to make electrodes because it can conduct electricity and as a lubricant because there are weak intermolecular forces and no covalent bonds so layers slide easily over each other.

Diamond is used in cutting tools as it is very hard due to its rigid structure.

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1.38 Explain the properties of fullerenes including C60 and graphene in terms of their structures and bonding

FULLERENES:

-simple molecule formed by carbons

-weak intermolecular forces between the molecules

-have low m/p

-make them soft/slippery

-molecules strong due to covalent bonding

-shaped like closed tubes or hollow balls. They're mainly made up of carbon atoms arranged in hexagons, but can also contain pentagons or heptagons

C60 - BUCKMINSTERFULLERENE

  • spherical fullerene

  • made up of 60 carbon atoms

  • strong bonds but weak forces between molecules

  • slippery

  • unstable as a solid at higher temperature

GRAPHENE

  • similar to fullerenes but not a simple molecule

  • 2D hexagonal sheet of carbon

  • strong covalent bond

  • allows delocalised electrons to move so good conductor of electricity

12
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1.39 Describe, using poly(ethene) as the example, that simple polymers consist of large molecules containing chains of carbon atoms

Polymers have very large molecules. Atoms in the polymer molecules are linked together by strong covalent bonds. Intermolecular forces between polymer molecules are relatively strong and so these substances are solids at room temperature.

13
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1.40 Explain the properties of metals, including malleability and the ability to conduct electricity

Malleable, the layers are able to slide over each other.

Can conduct electricity, delocalised electrons can move.

14
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1.41 Describe the limitations of particular representations and models to, include dot and cross, ball and stick models and two- and three-dimensional representations

The dot and cross model shows how electrons are shared in covalent bonds however they don't show the structure formed and they suggest that electrons in different atoms are different, when they are actually the same.

The metallic model shows the metal ions held in a lattice and explains why it conducts electricity, but the model does not show that the ions will be vibrating all the time.

3D ball and stick models show which atoms are joined together and show the shape of the structure. However, they also show the atoms too far apart and there are not really 'sticks' holding the atoms together,

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1.42 Describe most metals

Shiny solids which have high melting points, high density and are good conductors of electricity whereas most non-metals have low boiling points and are poor conductors of electricity

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