Module 3: Chemical patterns summary

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Formulae of elements and compounds

Chemical equations
Word equations (say what reacts and what is formed)
sodium + chlorine ----> sodium chloride
hydrochloric acid + calcium carbonate ----> calcium chloride + water + carbon dioxide
chlorine + potassium bromide ----> potassium chloride + bromine

Balanced chemical equations (write in formulae and check numbers of atoms of each element on each side are the same
2Na + Cl₂ ----> 2NaCl
Cl₂ + KBr ----> KCl + Br₂

State symbols
(s) = solid, (l) = liquid, (g) = gas, (aq) = aqueous = dissolved in water.
2Na(s) + Cl₂(g) ----> 2NaCl(s)
Ionic equations (leave out bits that do not change)
Cl₂ + Br^- ----> Cl^- + Br₂

The structure of atoms

3.01 The structure of an atom

Elements and the periodic table

3.02 The order of elements in the periodic table
Number of elements = about 100
Elements are building bricks of all materials
 

Elements in order of atomic number

3.03 The positions of metals and non-metals
metals on left                                                                                     non-metals on right

3.04 The positions of alkali metals, halogens and noble gases

alkali metals                                                                                    halogens  noble gases

3.05 The arrangements of electrons in shells
1st shell 2 electrons max
2nd shell 8 electrons max
3rd shell 8 electrons max
number of electrons = atomic number (find it in periodic table)
lithium 3 electrons 2,1
neon 10 electrons 2,8
sodium 11 electrons 2,8,1
chlorine 17 electrons 2,8,7
calcium 20 electrons 2,8,8,2

3.06 Group number and the number of outer electrons

3.07 Properties and the arrangement of electrons
Group 1 elements all have atoms with 1 outer electron. e.g. sodium 2,8,1
All of these atoms try to lose 1 electron so all react in the same way.
Group 1 elements all react with oxygen to form oxides, with chlorine to form chlorides and with water to form alkalis.

3.08 The change in property down a group
Despite the fact that all elements in the same group react similarly, there is a gradual change from top to bottom in each group. For example, lithium, sodium and potassium are in group with lithium at the top. When lithium is put in water, it fizzes, hydrogen is given off and an alkaline solution is left. Sodium reacts slightly more vigorously than lithium, but potassium reacts even more vigorously than that. This tells us that the alkali metals, going down from top to bottom act more vigorously with water as you go down the group

3.09 Properties of elements in the same group
Elements in the same group react in similar ways.  So all of the halogens like bromine react with iron.

The properties of halogens

3.10 The names of the halogens
Fluorine chlorine bromine iodine

3.11 The properties of the halogens
The colour of the Halogens changes from a lighter colour to a dark colour as we go down the group and the melting and boiling points increase as you go down the group. Fluorine at the top of the group is a yellow gas This colour changes to a yellow-green gas for chlorine, a red liquid for bromine and finally black solid for iodine at the bottom of the group.

3.12 The reactions of chlorine with sodium and iron
sodium + chlorine ----> sodium chloride
silver solid green gas      white solid
2Na + Cl₂ ----> 2NaCl
iron + chlorine ----> iron (III) chloride
                                 brown solid
2Fe + 3Cl₂ ---> 2FeCl₃
3.13 Displacement reactions of halogens
chlorine reacts with potassium bromide to form bromine
green                        colourless                           red
chlorine displaces bromine so chlorine is more reactive than bromine
chlorine + potassium bromide ---> bromine + potassium chloride
Cl₂(aq) + 2KBr(aq) ---> Br₂(aq) + 2KCl(aq)

chlorine reacts with potassium bromide to form bromine
green                        colourless                           red
chlorine displaces bromine so chlorine is more reactive than bromine
chlorine + potassium bromide ---> bromine + potassium chloride
Cl₂(aq) + 2KBr(aq) ---> Br₂(aq) + 2KCl(aq)

bromine reacts with potassium iodide to form iodine
red                          colourless                       brown
bromine displaces iodine so bromine is more reactive than iodine
bromine + potassium iodide ---> iodine + potassium bromide
Br₂(aq) + 2KI(aq) ---> I₂(aq) + 2KBr(aq)

3.14 The uses of chlorine
Chlorine is dissolved in sodium hydroxide to form bleach. This is used to make materials like cloth and paper white. Chlorine is also used to in swimming pools and drinking water to kill bacteria.

3.15 The use of iodine
Iodine is used as an antiseptic because it will kill the germs on the skin without damaging it.

Rates of reaction

3.16 The variation in rates of reaction
Some chemical reactions are slow like the rusting of iron.
Some chemical reactions are faster like the burning of wood..
Some chemical reactions are very fast like the explosion of gunpowder.

3.17 Factors that increase the rate of reaction
A chemical reaction speeds up (its rate increases) if
the temperature is increased (it is heated)
the concentration of a reactant is increased (less water in solution)
the surface area of a solid reactant is increased (it is cut up)
a catalyst is used 

3.18 Experiments to test the effect of factors on reaction rate

Concentration- Carry out the reaction between calcium carbonate and hydrochloric acid in a conical flask on an electrical balance for different acid concentrations but for the same volumes of acid, at the same temperatures and for the same masses of calcium carbonate. Record the mass every 30s for 10 minutes.

Surface area- Carry out the reaction between calcium carbonate and hydrochloric acid in a conical flask fitted with a stopper and a delivery tube to a measuring cylinder up side down in water. Use the same masses of powder (large surface area), small chips and large lumps (small surface area) of calcium carbonate with the same volumes, concentrations and temperatures of acid. Record the volume of gas formed every 30 seconds for 10 minutes.  The time to collect 100cm³ of gas could also be measured instead.

Catalyst - Carry out  the reaction between zinc and sulphuric acid in two test tubes.  In each test tube place the same mass of zinc, the same volume and concentration of acid and 5 drops of detergent.  Place 5 drops of copper sulphate solution into one of the test tubes.  Record the time for a 5cm depth of foam to build up in each teat tube.

3.19 Collision theory
              

3.20 The frequency and energy of collisions
few collisions in 1 second (small surface area, low concentration, low temperature) = slow reaction
many collisions in 1 second (large surface area, high concentration, high temperature)  = fast reaction
low energy collisions (low temperature) = slow reaction
high energy collisions (high temperature) = fast reaction

3.21 The effect of pH and temperature on reactions using enzymes

pH	rate of enzyme reaction	comments
low 1-5 acidic	very slow
neutral about 7	good rate	ideal pH
high 8-14 alkaline	very slow

temperature	rate of enzyme reaction	comments
cold	slow
40oC	fast	body temperature ideal
60oC +	slow	enzyme breaks down