The periodic table
- 1864- Newlands came up with his Law of Octaves. He:
- noticed that every 8th element was similar
- didn't leave gaps
- mixed up metals and non metals
- put elements with different properties in the same groups
- people only knew how to categorise stuff by atomic mass, they didn't know about atomic number because they didn't know about atomic numbers.
- 1869- Mendeleev came up with a table of elements. he knew about 50 elements so he had more material to work with. He: left gaps that ended up predicting properties of undiscovered elements and kept elements with similar properties in the same groups
- Not all scientists thought this was important- there wasn't a lot of evidence to support it all. When the newly discovered elements fit Mendeleev's patterns he was chuffed and the scientists were all convinced. Then they found out about electronic structure and believed that the periodic table was actually pretty important.
- The modern periodic table is pretty simple and you know most of it but shielding is where inner electrons get in the way of nuclear charge. Distance+shielding=electrons in higher energy levels -> more easily lost
The Alkali Metals
Group 1- Alkali Metals:
- More reactive as you go down the group- outer electron more easily lost (further from nucleus)
- Lower melting and boiling points
- Low density -> first 3 in the group less dense than water
- Form ionic compounds with non-metals
- Produce white compounds that dissolve in water to form colourless solutions
- Reaction with water produces hydrogen gas and hydroxides that dissolve in water to give alkaline solutions
- good conductors of heat and electricity
- dense, strong, shiny
- less reactive than group 1 metals
- much denser, stronger and harder than group 1 metals and much higher melting points (except mercury)
- often more than one ion e.g. Fe2+/Fe3+, Cu+/Cu2+
- different ions usually form different-coloured compounds
- compounds are colourful
- make good catalysts:
-iron in the haber process
-manganese (IV) oxide in decomposition of hydrogen peroxide
-nickel useful for turning oil into fats (margarine)
Hard and Soft Water
- Soft water readily forms lather with soap. Hard water reacts with soap to form scum and so more soap is needed to form lather. Soapless detergents do not form scum.
- Hard water contains dissolved compounds, usually of calcium or magnesium. The compounds are dissolved when water comes into contact with rocks.
- There are two types of hard water. Permanent hard water remains hard when it is boiled. Temporary hard water is softened by boiling.
- Temporary hard water contains hydrogencarbonate ions (HCO3––) that decompose on heating to produce carbonate ions which react with calcium and magnesium ions to form precipitates.
- Using hard water can increase costs (more soap is needed.) When temporary hard water is heated it can produce scale that reduces the efficiency of heating systems and kettles. Hard water has some benefits because calcium compounds are good for the development and maintenance of bones and teeth and also help to reduce heart disease.
- Hard water can be made soft by removing the dissolved calcium and magnesium ions. This can be done by adding sodium carbonate, which reacts with the calcium and magnesium ions to form a precipitate of calcium carbonate and magnesium carbonate or using commercial water softeners such as ion exchange columns containing hydrogen ions or sodium ions, which replace the calcium and magnesium ions when hard water passes through the column.
- Water of the correct quality is essential for life. For humans, drinking water should have sufficiently low levels of dissolved salts and microbes.
- Water filters containing carbon, silver and ion exchange resins can remove some dissolved substances from tap water to improve the taste and quality.
- Chlorine may be added to drinking water to reduce microbes and fluoride may be added to improve dental health.
- Pure water can be produced by distillation.
- Water treatment goes like this: mesh screen flitering, chemicals added to combine solids and microbes and make them fall to the bottom, water filtered through gravel beds, water is chlorinated.
- Adding Flouride and Chlorine to water has disadvantages:
-Adding chlorine to water could increase cancer
-Flouride in high doses can cause cancer and bone problems
-Some people think it's a mass medicate to add Fluoride to water -> they don't get a choice
Energy from reactions
- The relative amounts of energy released when substances burn can be measured by calorimetry, eg by heating water in a glass or metal container. This method can be used to compare the amount of energy released by fuels and foods.
- Energy is normally measured in joules (J). Q = mc ΔT.
- The amount of energy released or absorbed by a chemical reaction in solution can be calculated from the measured temperature change of the solution when the reagents are mixed in an insulated container. This method can be used for reactions of solids with water or for neutralisation reactions.
- Simple energy level diagrams can be used to show the relative energies of reactants and products, the activation energy and the overall energy change of a reaction.
- During a chemical reaction: energy must be supplied to break bonds and energy is released when bonds are formed.
- In an exothermic reaction, the energy released from forming new bonds is greater than the energy needed to break existing bonds. In an endothermic reaction, the energy needed to break existing bonds is greater than the energy released from forming new bonds.
- Catalysts provide a different pathway for a chemical reaction that has a lower activation energy.
- Hydrogen can be burned as a fuel in combustion engines (hydrogen + oxygen water) and it can also be used in fuel cells that produce electricity to power vehicles.
- THIS IS WHERE YOU NEED ALL THE STUFF FROM MY SONG
- Carbonates react with dilute acids to form carbon dioxide. Carbon dioxide produces a white precipitate with limewater. This turns limewater cloudy.
- Halide ions in solution produce precipitates with silver nitrate solution in the presence of dilute nitric acid.
- Silver chloride is white, silver bromide is cream and silver iodide is yellow.
- You should be able to calculate the chemical quantities in titrations involving concentrations (in moles per dm3) and masses (in grams per dm3).
- Sulfate ions in solution produce a white precipitate with barium chloride solution in the presence of dilute hydrochloric acid.
- The volumes of acid and alkali solutions that react with each other can be measured by titration using a suitable indicator.
- If the concentration of one of the reactants is known, the results of a titration can be used to find the concentration of the other reactant.
- The raw materials for the Haber process are nitrogen and hydrogen. Nitrogen is obtained from the air and hydrogen may be obtained from natural gas or other sources.
- The purified gases are passed over a catalyst of iron at a high temperature (about 450 °C) and a high pressure (about 200 atmospheres). Some of the hydrogen and nitrogen reacts to form ammonia. The reaction is reversible so ammonia breaks down again into nitrogen and hydrogen: nitrogen + hydrogen ammonia. On cooling, the ammonia liquefies and is removed.The remaining hydrogen and nitrogen are recycled.
- When a reversible reaction occurs in a closed system, equilibrium is reached when the reactions occur at exactly the same rate in each direction.
- The relative amounts of all the reacting substances at equilibrium depend on the conditions of the reaction.
- If the temperature is raised, the yield from the endothermic reaction increases and the yield from the exothermic reaction decreases and vice versa.
- In gaseous reactions, an increase in pressure will favour the reaction that produces the least number of molecules as shown by the symbol equation for that reaction.
- These factors, together with reaction rates, are important when determining the optimum conditions in industrial processes, including the Haber process
- Alcohols contain the functional group –OH. Methanol, ethanol and propanol are the first three members of a homologous series of alcohols.
- Methanol, ethanol and propanol:
- dissolve in water to form a neutral solution
- react with sodium to produce hydrogen
- burn in air
- are used as a fuels and solvents, and ethanol is the main alcohol in alcoholic drinks.
- Ethanol can be oxidised to ethanoic acid, either by chemical oxidising agents or by microbial action.
- Ethanoic acid is the main acid in vinegar.
- Ethanoic acid is a member of the carboxylic acids, which have the functional group –COOH.
- Carboxylic acids:
■ dissolve in water to produce acidic solutions
■ react with carbonates to produce carbon dioxide
■ react with alcohols in the presence of an acid catalyst to produce esters
■ do not ionise completely when dissolved in water and so are weak acids
■ aqueous solutions of weak acids have a higher pH value than aqueous solutions of strong acids with the same concentration.
- Ethyl ethanoate is the ester produced from ethanol and ethanoic acid. Esters have the functional group –COO–. They are volatile compounds with distinctive smells and are used as flavourings and perfumes.
Group 7- The Halogens
- Less reactive as you go down the group- harder to gain electrons (outer shell further from nucleus)
- Higher melting and boiling points
- All non-mentals with coloured vapours:
- Flourine-reactive poisonous yellow gas
- Chlorine- reactive poisonous dense green gas
- Bromine- dense poisonous red-brown volatile liquid
- Iodine- dark grey crystalline solid or purple vapour
- All exist as molecules (pairs of atoms)
- Halogens form ionic bonds with metals
- More reactive halogens displace less reactive ones (Brangelinaniston)