Chemistry Unit C3 Revision Notes

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Chemistry Revision Notes
C3-1: The Periodic Table
In the 19th century scientists didn't know much about the structure of atoms. Scientists tried to
categorise elements based on their properties and their atomic weights.
1863 Newlands proposed the law of octaves (similar properties repeated every 8th element) But
after calcium in the 62 elements known at this time this rule didn't seem to work. Scientists didn't
accept his work.
1869 Mendeleev produced a better table with gaps for unknown elements so groups with similar
properties worked. He predicted the properties of these unknown elements. When some of these
missing elements were discovered they matched Mendeleev's predictions this made other scientists
accept his idea. His table became the basis for the modern periodic table.
At the start of the 20th century, scientists discovered protons and electrons, then discovered the
arrangement of electrons in the atoms. The elements in the periodic table were arranged in their
atomic number and were lined in vertical groups.
The element groups have similar chemical properties because their atoms have the same number of
electrons in their outer shell. For most elements the number of electrons in their outer shell is the
same as their group number.
Group 1 in the periodic table is called the alkali metals. Their properties include:
React well with water and air
Soft solids at room temperature
Low melting and boiling point
Low densities
React with water to produce hydrogen gas and a metal hydroxide that is an alkali
One electron in their outer shell, which they lose in reactions to form ionic compounds with a
single positive charge
React with the halogens to form salts that are white or colourless crystals
The reactivity of the alkali metals increases as you move down the group. This is because there is less
attraction to the centre of the atom meaning the one electron is easier to lose as there is more
The transition elements/metals are found between group 2 and 3 in the periodic table. Except for
mercury they have a higher melting and boiling point than the alkali metals. They are malleable and

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They react slowly or not at all with oxygen and water at
normal temperatures and they are strong and dense and used as building materials, often as alloys.
They form positive ions with various charges (Fe2+, Fe3+..)
Their compounds are usually brightly coloured and many are used as catalysts in chemical reactions.
Group 7 in the periodic table is called the halogens, they are non-metallic elements. They usually
travel in pairs as molecules.…read more

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Temporary hard water contains hydrogencarbonate ions which decompose when heated to produce
carbonate ions, water and carbon dioxide. The carbonate ions react with the calcium/magnesium ions
in the water to produce precipitates of calcium/magnesium carbonate that are deposited as scale.
Another method is an ion-exchange column packed with resin containing sodium or hydrogen ions.
When hard water is passed through the resin calcium/magnesium ions become attached to the resin
and sodium and hydrogen ions take their place, due to displacement. These don't react with soap.…read more

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We can show the energy changes for chemical reactions on energy level diagrams. The difference
between the energy levels of the reactants and the products is the energy change for a reaction.
During a chemical reaction the reactants must break their bonds, breaking bonds is endothermic
because energy is taken in.
The minimum energy for this to happen is the activation energy.
When new bonds are formed energy is released so is exothermic.…read more

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To find the difference between Aluminium, Calcium and Magnesium add excess sodium hydroxide
solution and the precipitate of aluminium hydroxide dissolves.
There are three tests for negative ions:
1. Carbonate ions: Add dilute hydrochloric acid to the substance to see if it fizzes. If it does and
a gas is produced which turns limewater milky, the substance contains carbonate ions.
2.…read more

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If we know the volume of a solution and its concentration we can work out the mass or the number of
moles in the substance in any volume of solution.
Question examples:
1. 50cm³ of solution was made using 5.6g of potassium hydroxide (KOH). What is its
concentration in
1cm³ of solution contains: 5.6 / 50 grams = 0.112
So 1dm³ of solution contains: 0.…read more

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In a closed system no reactants or products can escape. Equilibrium is reached when the rate of the
forward action is equal to the rate of the backwards reaction, but the amounts of the amount of
product and reactant remains constant.
To change the amount of product or reactants the reaction conditions can be changed.
If you increase the concentration of reactant more product will be formed as the system tries to
reach equilibrium.…read more

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The lower the temperature the greater the yield of ammonia, however at lower temperatures the
rate of reaction slows and an iron catalyst becomes ineffective so it would take longer to produce
ammonia. Therefore a compromise of temperature is usually between 200-450°C.
C3-5: Organic Chemistry
Organic molecules form the basis of living things and all contain carbon atoms. Carbon atoms react
covalently to each other to form the `backbone' of many series of organic molecules.
Alcohols contain the function group ­O-H.…read more

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Acids that don't ionise completely are known as weak acids. In aqueaous solutions of equal
concentration, weak acids have a higher pH and react more slowly than strong acids.
Esters are volatile compounds and have distinctive smells that may be pleasant and fruity so are used
in perfumes.…read more


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