AQA Additional Chemistry C2

Chemistry additional units. Pre-2011 spec. AQA board. 

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  • Created on: 24-01-12 18:39

Subatomic Particles

There are three main parts to an atom:

  • Neutrons - they form part of the nucleus. The role of the neutrons is too bond together the nucleus as the positive charges from the protons would repel otherwise. They have no charge, and a relative atomic mass of 1.
  • Protons - they form part of the nucleus. They have a positive charge, and a relative atomic mass of 1. 
  • Electrongs - they surround the nucleus, and are structured in energy shells. They have the relative atomic mass of (approx) 0, and a negitive charge. 

Electron configeration goes in the order...

2, 8, 8

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Reading the periodic table

The periodic table is split into groups. Each group has certain properties. 

  • Group 1 - all have 1 electron on the highest occupied energy shell.
  • Group 2 - all have 2 electron on the highest occupied energy shell etc...
  • Group 8 - fully occupied energy shells.. eg 2,8 or 2,8,8

They all have similar properties because of the electron structure. Every atoms aims to have a stable electron structure which means it has a fully occupied shells. It does this by losing or gaining electrons, or sharing electrons. The most reactive elements are those that are close to getting fully occupied shells. eg. 2,7 or 2,8,1

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Simple Molecular Compounds

These are any compounds which have basic structures. 

  • They have weak intermolecular forces, so they have low boiling and melting points
  • Strong bonds between two atoms, which means they are hard to decompose.
  • They don't conduct electricity
  • They don't have an overall charge. 
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Ionic Bonding

Ionic bonding exists between a metal and a non-metal, and it is the loss and gain of electrons to create an electrostatic attraction between the molecules. It produces a positive (metal) ion as it losses electrons, and a negative (non-metal) ion as it gains electrons.

A dot and cross diagram is used to show this:

  • Remember to show the charge of each ion
  • Remember to show the dots and cross to show the transfer of electrons
  • Check the data sheet to ensure you form the right ion.
  • It should have a full energy shell

Ionic compounds have high boiling and melting points as they often form giant ionic structures (lattices).

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Covalent Bonding

This is between two non-metals when they SHARE electrons so that they gain the complete amount of electrons in the outer shell to gain a stable arrangement. 

Many covalent compounds are small such as O2 and HCl, however they can form giant lattice structures. 

Covalent bonding is strong, and requires high temps to break, however there is often a weak intermolecular force holding the molecules together, so they have low boiling and melting points

Example:

(http://www.google.co.uk/imgres?q=covalent+bonding&um=1&hl=en&sa=N&biw=1366&bih=667&tbm=isch&tbnid=1Et9jnNqHujFRM:&imgrefurl=http://www.chemguide.co.uk/atoms/bonding/covalent.html&docid=rwz8Lat3Drv37M&imgurl=http://www.chemguide.co.uk/atoms/bonding/ch4nh3h2o.GIF&w=401&h=152&ei=TyEfT-HAHMzxsgazj7XEDA&zoom=1&iact=hc&vpx=616&vpy=224&dur=4900&hovh=121&hovw=320&tx=126&ty=54&sig=107059570057657985076&page=1&tbnh=68&tbnw=179&start=0&ndsp=19&ved=1t:429,r:3,s:0)

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Giant Covalent Structures

An example of this is the diamond, which forms 4 bonds, and has no weaknesses in the structure as it is one giant lattice. Every single bond is a strong covalent bond between carbon atoms. It makes diamond a very high boiling point and also a very strong substance.

Graphite is another example, it forms 3 bonds, and this leaves a de-localised electron. This free electron means it is free to conduct electricity. Graphite is also as lucubration, and there are weak attractions between each layer of graphite which means the layers can move over each other easily. 

Silicon Dioxide is a strong covalent structure and forms a lattice, where there are very few weak bonds. This makes it strong and have a very high boiling point.

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Giant Ionic Structures

Giant ionic structures are held together by electrostatic attractions between the positive and negative ions. They form as a lattice, and have high boiling and metaling points as the electrostatic attractions are very strong.

They also conduct electricity, but only when dissolved in water or as a liquid. This is because the ions then free to move and carry a current. 

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Metallic Structures

As pure metals, they are malleable and soft, This is because the layers are easy to move over each other. 

They often form as lattices, with de localised electrons in-between the positive ionic metals. The electrons can freely move which allows the conduction of electricity.  

The electrostatic attractions between the postive ions and electrons hold the metal together. 

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Nanaparticles

These are particles which we interactive with on the nano scale (1 billionth of a metre = 1nm). We can combine nano particles to form nano structures, which have many uses. 

Nano particles have different properties of the same material in bulk, for example...

  • electrons can move thorough a layer of atoms,
  • sensitive to light, heat, and magnetism
  • high surface area to volume ratio.

Nano structures often conduct, are very strong and have a huge surface area. They can be used as catalysts and nano tubes are very variable in use.

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Nancomposites

We can add materials to plastic to make strong, stiffer and lighter materials. These materials are called Nano composites. 

A type of nano composite is the use of smart materials. These materials are often shape memory, and are sensitive to heat, light and behave in certain ways to other conditions. This makes them useful in cars, glasses, drug injections, construction and catalysts. 

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Evaluation of Smart and Nano Materials

Smart Materials - Advantages:

  • Many different properties,  many applications  east to manipulate, potential uses

Disadvantages 

  • cost

Nano materials

  • Ad: many applications, can reduce costs as catalysts, uses in medicine
  • Dis: difficult to engineer, dangerous in water supplies (unknown effect on nature), could develop dangerous materials
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Relative Atomic Mass and Formula Mass

Relative Atomic mass is the mass of the neutrons and protons added together. 

Relative Formula Mass is the addition of all the atomic masses of the atoms in the molecule. Remember that there are normally more than one of an atom in a compound... eg 2 hydrogen in H2O

Isotopes are the same element however they have different atomic masses as they have different numbers of neutrons. 

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Percentage Mass of an Element in Compound

Percentage mass  =

(relative mass of element in compound./ relative formula mass) x 100

eg....

MgO

Relative mass of Mg = 24

Relative mass of Oxygen = 16

24 + 16 = 40

Percentage mass of Mg = (24/40) x 100 = 60%

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Empirical Forumla

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The Mole

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Mass of Product

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Mass of Reactants

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Percentage Yield and Atom Economy

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Haber Process

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Haber Process Evaluation

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Rate of Reactions

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Rate: Temperature

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Rat: Concentration

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Rate: Surface Area

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Rate: Cayalysts

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Analysing Rate of Reaction

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Exothermic and Endothermic Reactions

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Reversible Reactions

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Controlling Reversible Reactions

Temperature - An increase in temperature will mean that the reaction which is endothermic as the equilibrium try to make up the difference again. A decrease in temperature would increase the exothermic, as the equilibrium try to increase the temp to create a balance.  

Pressure - an increased pressure will always led to the side with the least molecules being produced being favoured. This is an attempt to reduce the pressure. 

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Haber Process; Compromise Solution

in the haber process, we use a quite high temp, so that the reaction is fast, however this doesn't favour the yield, as the rate of decomposition increases at a high temp. 

We use a high pressure in the haber process, even though it is expensive to maintain, as a high pressure favours the fewer molecules of the ammonium production. We can't have it too high however because of cost.

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Electrolysis

This is the separation of ionic compounds using electricity. 

Ionic compounds allow an electric current through them in aqua's solutions and as liquids as they are ionic movement. 

The ion with the least reactivity will form at the electrodes, as it takes less energy. The positive ions are attracted to the negative, and the negative ions are attracted to the positive.

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Redox and Precipitation Reactions

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Electrolysis: Half Equations

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Industrial Electrolysis

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Neutralisation

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Soluble Salts from Metals

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Salts of Alkali Metals

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Soluble Salts from Insoluble Bases

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