Chemistry C3 AQA - Periodic Table

During the 19th century, chemists were trying to organise the elements they were finding.

John Dalton came up with the 1st idea - He arranged them in order of mass.

John Newlands added to this, with his law of octaves based on the observation that the properties of every 8th element was similar. However, he assumed all the elements had been discovered, and filled it all in, dispite some of the elements not being similar at all.

Dmitri Mendeleev arranged the known elements in a table (about 50 of them). he arranged them in order of atomic masses. He then arranged them so that a periodic pattern in their physical and chemical properties could be seen. He also left gaps for new element, and predicted what their properties should be

Mendeleev's table was the basis for the modern table. However not all elements are arranged in order of mass (eg. Potassium and Argon).

We now arrange the elements in order of their atomic number, which puts them all in exactly the right places.

Called ALKALI METALS.

React with water to produce HYDROGEN and an ALKALINE sloution containing the metal hydroxide (eg 2K(s) = 2H2O(l) --> 2KOH(aq) + H2(g) )

The REACTIVITY of the alkali metals INCREASES as we go DOWN the group. (Lithium being the least reactive, Francium the most)

Group 1 metals have a LOW DENSITY. (Litium, Sodium and Potassium all float on water)

They are silvery and shiny, but quickly go dull as they oxidise.

They MELT and BOIL at LOW temperatures, as we go DOWN the group, the melting and boiling points DECREASE.

The Alkali Metals are very reactive due to their electronic structure, they only have 1 electron in their outer shell. This means they only have to lose 1 electron to obtain a stable electronic structure. 

THey react with non-metals, losing their 1 outer electron, and form a metal ion with a 1+ chage.

They always form Ionic compounds, which means they form crystals. Both the compounds and the metal chlorides dissolve easily in water.

Are all POISONOUS non-metals with COLOURED vapours.

They have LOW melting and boiling points.

They all look very different.

Chlorine can be tested for with damp litmus paper - it will be BLEACHED.

Bromine is a dense orange/brown liquid which vapories quickly - it is volatile.

Iodine is a dark grey crystalline solid which produces violet-cloured vapour when heated.

All Halogens exist as DIATOMIC molecules. (They go around in pairs)

The Halogens all react with metals, they gain 1 electron, forming ions with a 1- charge.In these reactions, METAL HALIDES are formed, eg Iron(III) Bromide (FeBr3) 

Halogens reacted with non-metals form COVALENT BONDS.

Many transition elements have similar properties, but are different from the other elements in the Periodic Table.

The metals's atoms exist in a giant structure held together by metallic bonds, and the outer electrons of each atom can move freely within the metal.

They are GOOD conductors of ELECTRICITY and HEAT, because DELOCALISED electrons can carry the electrical currrent or the heat energy through the metal.

The Transition metals are also HARD, TOUGH, and STRONG yet MALLEABLE.

The transition metals have very high melting points (with exception of mercury, which is liquid at room temperature)

Transtions metals corrode SLOWLY, as they are LESS reactive than group 1 & 2 metals. They are all very useful in alloys.

Transition Metals form COLOURFUL compounds. We use this in many ways, for example in pottery glazing. It is also why many rocks/minerals/gem stones have colours.