The Alkali metals
- The elements of group 1 of the periodic table are called the alkali metals
- The metals all react with water to produce hydrogenn and an alkaline solution containing the metal hydroxide
- The reactivity of the alkali metals increases as we go down the group
- The halogens exist as diatomic molecules
- They have low melting points
- they are poor conductors of heat and electricity
- The halogens all form ions with a negative charge
- The halogens form covalent compounds by sharing electrons with other non-metals
- The reactivity of the halogens decreases going down the group
The Transition elements
- Nearly all the transition elements have high melting points and high densities
- The transition metals are strong and hard, and are good conductors of heat and electricity
- The transition metals do not react vigorously with oxygen or water
Reactive metals: react vigourously with other elements like oxygen or chlorine and with water. They are all soft- some can even be cut with a knife like cheese!
Transition metals: Contain elements than most people think of when they hear the word "metal". These metals are not really reactive. Some like gold and silver are so unreactive they are called noble metals.
Non-metals: Have low melting and boiling points and many are liquids or gases at room temperature and pressure.
Noble gases: These non metal elements are very unreactive and its very difficult to get them to combine with other elements.
The early periodic table
- John Dalton is a teacher from manchester, he arranged the elements in order of mass measured in various chemical reactions. In 1808 he published a table of elements in his book.
- 1863 John Newlands built on Daltons idea with his law of octaves. He based his idea on the observation that every eighth element seemed similar. He was so determinedf to make it work he made vital mistakes. He didnt leave spaces for new elements and he put them in his octave order even though some didnt even fit in.
- 1869 Russian scientist Dmitri Mendeleev arranged the elements in a table in order of their atomic masses, he arranged them so their physical and chemical properties could be seen. He even left gaps for new elements. He is remembered as the father of the modern periodic table.
Strong and weak acids/alkalis
- Acids in aqueous solutions produce H+ ions.
- Alkalis in aqueous solutions produce OH- ions.
- A strong acid or base is 100% ionised in water
- A weak acid or alkali is only partly ionised in water
- An acid is a proton donor.
- A base is a proton acceptor.
- Titration is used to measure accuratly how much slksli is needed to react completely with a known amount of acid (or vice versa)
- The poin of which an acid-base reaction is complete is called the end point of the reaction
- A suitable indicator should be chosen to show the end point of an acid-base reaction
- Pipette measures out fixed volume of solution
- Burette measured the volume of solution added.
- To calculate the concentration of a solution
1. Calculate the mass in grams of solute in 1cm3 of solution.
2. Calculate the mass in grams of solute in 1000cm3 of solution
3. Convert the mass on grams to moles
- To calculate the mass in grams of the solute in a certain volume of solution
1. Calculate the mass in grams of the solute there is in 1dm3 of solution,
2. Calculate the mass in grams of the solute in 1cm3 of solution
3. Calculate the mass in grams of sulute there is in the given volume of the solution
Water and solubility
- Water evaporates from rivers, lakes and oceans and condenses to form clouds returning to the surface as rain
- Most ionic substances are soluble in water but many covalent compounds are not.
- A saturated solution contains the maximum amount of solute that will dissolve at that temperature.
- The solubility of most solid solutes increases with temperature
- The solubility of gases decreases with increasing temperature
- Solubility curves show how the solubility of a substance changes with temperature.
- Hard water contains dissolved substances such as calcium and magnesium salts.
- The calcium and/or magnesium ions in hard water react with soap producing a precipitate called scum
- The calcium salts and /or magnesium salts also decompose to form scale when the water is heated.
- Hard water may have benifits for human health
Removing hardness - Soft water
- Soft water does not contain salts that produce scum or scale.
- Hard water can be softened by removing the salts that produce scum and scale
- Water can be softened by adding washing soda or by using an ion exchange resin to remove calcuim and magnesium ions
- Water for drinking should contain low levels of dissolved substances and microorganisms.
- Water is made fit to drink by filtering it to remove solids and adding chlorine to kill bacteria
- We can make pure water by distillation
Comparing the energy produced by fuels
- When fuels and food react with oxygen, energy is released. The reaction is exothermic.
- Asimple calorimeter can be used to compare the energy released by different fuels or different foods in a school chemistry lab.
Energy changes in reactions
- In chemical reactions energy must be supplied to break the bonds between atoms and reactants.
- When bonds are formed between atoms in a chemical reaction energy is released.
- In an exothermic reaction, the energy released when the bonds are formed is greater than the energy absorbed when the bonds are broken the opposite is true for endothermic reactions.
- (Triangle)H is negative for exothermic reactions. It is positive for endothermic reactions.
- The minimum amount of energy to start a reaction is called the aviation energy
Calculations using bond energies
- To calculate the energy change fir a chemical reaction we need to work out
- 1. How much energy is needed to break the chemical bonds in the reactants and
- 2. How much energy is released when the new bonds are formed in the products.
- The overall energy change in a chemical reaction can be calculated using bond energies.
Tests for Positive Ions
- Group 1 and group 2 metals can be identified in their compounds using flame tests
- Sodium Hydroxide solution can be used to identify different metal ions depending on the precipitate that is formed
- Ammonium ions produce ammonia when sodium hydroxide solution is added and the solution is warmed gently
Colours under flame test
- Lithium- Bright red
- Sodium- Golden yellow
- Potassium- Lilac
- Calcium- Brick red
- Barium- Green
Tests for negative ions
- We identify carbonates by adding dilute acid, which produces carbon dioxide gas
- We identify halides by adding nitric acid and silver nitrate solutionnwhich produce a precipitate of silver halide.
- We identify sulfates by adding hydrochloric acid and barium chloride solution to produce a white precipitate of barium sulfate
- We identify nitrates by adding sodium hydroxide solution and a little aluminium powder to produce ammonia gas.