Newland - Ordered the few elemenets known at the time
in order of atomic weight. After Calcium they didnt match
the pattern and his ideas weren't accepted.
Mendeleev - Organised by similarities in properties. He
left gaps for unknown elements, after these were
discovered his predictions were confirmed and they
accepted the idea.
Developed by attempts to classify the elements.
The Modern Periodic Table
Organised by proton (atomic) number.
Atoms in the same group have similar properties as they have the same
number of electrons in their outer shell.
Group number = the amount of electrons in the outer shell.
Trends in reactivity can be explained as we go down a group in terms of:
- the distance between the outermost electrons and the nucleus.
- number of energy levels (shells).
Reactivity of metals increases as we go down the group.
Reactivity of non-metals decreases as we go down the group.
Group 1 - The Alkali Metals
React readily with air and water.
Reacts with water to produce Hydrogen Gas and a alkali Metal Hydroxide.
Low melting and boiling points, low
density. Soft solids at room
temperature.
Form +1 ions (ionic compound).
Reacts with Group 7 to form white salts or colourless crystals.
Reactivity increases as you go down the group.
Transition Elements
They are all metals.
Higher melting and boiling points that Group 1.
Malleble.
Good conductors of heat and electricity.
React slowly or not at all with oxygen or water.
Strong and dense, useful as building materials,
especially as alloys.
Form positive ions with various charges eg. Fe2+ Fe3+
Compounds of transitions metals are often brightly coloured.
Many work well as catalysts.
Group 7 - The Halogens
Non-metals.
Low melting and boiling points that increase
further down the group.
Form -1 ionic compounds.
Bond covalently with non metals.
More reacitve halogens can displace a less reactive one from a
solution of a halide (halogen) compound.
Reactivity decreases down the group.
Water
Hard Water
Uses more soap to produce an effective lather.
Contains dissolved compounds eg. Calcium and Magnesium salts.
These react with the soap to form a precipitate called scum.
Temporary hard water can produce a solid scale when heated, reducing efficiency of appliances.
Better than soft water for maintaining teeth and bones.
Soft water lathers easily.
Removing Hardness
Soft water may have dissolved compounds but they
don't react to produce scum.
Can be done by removing the dissolved compounds.
Temporary hardness can be removed by heating. Permanent hardness cannot.
Both types can be softened by adding washing soda or by using an
ion-exchange resin to remove the calcium and magnesium ions.
Water Treatment
Drinking water shouldn't contain any harmful
substances and only contain low levels of dissolved
substances and microbes.
Water can be made fit to drink by filtering it to remove solids then disinfecting it to kill of any microbes.
Pure water can be made my distillation but this requires a lot
of energy, making it expensive.
Water Issues
Advantages & Disadvantages of water treatment.
Water can be treated to remove microbes, hardness and
improve dental health.
Chlorine is particularly effective at killing microbes but it is poisonous
and can produce other toxic compounds. So it must be used carefully.
Fluoride compounds are added to toothpaste to help prevent decay. People say that they should be able to
choose to take extra fluoride or not and that it should not be added.
Energy Calculations
Comparing Energy Released by Fuels
When fuels and food react with
oxygen they release energy in an
exothermic reaction.
Calorimeters can compare energy
released by different fuels/foods.
Simple Calorimeter: Water in a
beaker, burn a substance and
temperature rise of water
depends on the energy
released.
Q= m*c*tempchange
Q=energy transferred(J)
c= specific heat capacity
Energy Transfers in Solutions
Energy is transferred to or out of the solution.
Measure temperature change then use the equation Q=m*c*temp
Neutralisation and
displacement reactions are both
examples of reactions where we
can use this technique.
Energy Level Diagrams
Show the relative different in the energy of reactants and the energy of the products
Catalysts provide a lower activation energy.
Bond breaking, energy taken in - Endothermic.
Bond making, energy given out - Exothermic
Calculations Using Bond Energies
Exothermic - Energy
released when bonds are
formed is greater than the
energy absorbed when
bonds are broken.
Endothermic - Energy released when
new bonds are formed is less then the
energy absorbed when the bonds are
broken.
Analysis and Synthesis
Testing for Positive Ions
Flame Test
Calcium - (Brick) Red
Potassium - Lilac
Lithium - Crimson
Sodium - Yellow
Barium - Green
Burn the substance.
Sodium Hydroxide Solution
Aluminium, Calcium and Magnesium form
a white precipitate when NaOH is added to
any solution containing them.
Ass excess NaOH to test for Mg (Precipitate will dissolve).
Ca and Mg can be determined using a flame test.
Testing for Negative Ions
Carbonate
Two test tubes, one with acid and carbonate,
with bung and pipe leading to another test
tube with limewater.
Add dilute HCl acid to the substance to see if it fizzes.
If it does, the gas turns the lime water cloudy and
carbonate ions are present.
Hailde Ions
Add dilute nitric acid then silver nitrate solution
and a ppt will form.
Chloride Ions - White ppt.
Bromide Ions - Cream ppt.
Iodide Ions - Yellow ppt.
Sulphate Ions
Add dilute HCl acid and then
Barium Chloride solution. If a
white precipitate forms,
sulphate ions are present.
Chemical Analysis
Used in environmental, medical and forensic analysis.
Qualitative - Tests if a substance is in a sample.
Quantitative - Test how much of a substance is in a sample.