Early Periodic Table
1808 - John Dalton arranged discovered elements in order of their masses, which he measured in various calculations and experiment.
1863 - John Newlands built on Dalton's idea with the law of octaves. An idea that elemental properties were shared in every eighth element. However, in this idea he made several mistakes, he assumed that every element had been found, he filled in his table using the law of octaves when some elements were not similar at all and even put two elements in the same place to make his law of octaves work.
1869 - Dimitri Mendeleev drew up a new periodic table, he placed elements in order of atomic mass and also left gaps in his table for new elements to be discovered. He is remembered as the father of the modern periodic table.
A random fact: In 1900 Dmitri Mendeleev was attacked by the mentally disabled son of John Newlands, Christopher Maddocks Newlands. Christopher came at him brandishing a large blade and threatened to "eat his own hands" while Mendeleev was eating at a restaurant in Paris.
Modern Periodic Table
Mendeleev's ideas were very good, but they had floors. If we still used his table, we would be putting noble gasses next to highly reactive gasses in the periodic table. Bad idea.
Today we arrange our periodic table in order of their atomic number and atomic structure, we started doing this since the early 20th century.
Elements in the same periodic group have similar properties for they have the same amount of electrons in their outer shell.
As we go down a group, the number of occupied energy levels increases and so does the size of the atom. This means there are more energy levels between the atom and the outer shell, so the forces between them are weaker.
- With a large atom it is more easy it is to loose electrons
- With a large atom it is less easy it is to gain electrons
Group 1 - the Alkali Metals
In Group 1 - the number of occupied energy levels increases and so does the size of the atom. This means there are more energy levels between the atom and the outer shell, so the forces between them are weaker. the reactivity increases going down the group for the outer electron is more easy to loose, so elements lower down the group are more reactive.
All of the alkali metals are highly reactive for they only have one electron in their outer shell and therefore have to be kept in oil to stop them from reacting with oxygen in the air.
All of the metals have very low densities, so low that we can cut them with a knife and some even float on water, they also have low melting points (for metals).
They always react with non-metals, losing the singular outer electron and forming a metal ion carrying a 1+ charge. When they react with water they normally fizz and forms hydrogen gas also producing a metal hydroxide, which is soluble in water and produce a colourless solution with a high Ph.
Alkali metals also react with other non-metals, like chlorine. They produce metal chlorides (white solids which dissolve in water and form a colourless solution.) Alkali metals also react with liquids like fluorine, bromine and iodine, all of these when they react create ionic metal compounds which form crystals and dissolve in water.
Group 7 - the Halogens
They are all poisonous non-metals which give off coloured vapours. They are all covalently bonded molecules made up from pairs of atoms like oxygen - O2. They have low melting points and boiling points and are poor conductors of heat and electricity.
They all look different at room temp and are all poisonous -
- fluorine is very reactive pale yellow gas.
- chlorine is a very reactive dense green gas (you can test for chlorine by putting a piece of damp litmus paper over the gas, if it bleaches the gas is chlorine.)
- Bromine is a dense dark orange/brown liquid which vapourises easily - its volatile.
- Iodine is a dark grey crystalline solid which produces a violet colour when heated.
Elements become less reactive as you go down the group (outer shell further away from attractive force of nucleus, therefore harder to attract electrons.) They react with metals to form ionic compounds and with non metals to form covalent compounds.
The Transition Elements
The transition metals or elements are in the middle of the periodic table between groups 2 and 3, they all form positive ions with various charges.
Like metals they are malleable, have high melting points, they're strong (thanks to their metallic bonds) and good conductors (thanks to their localised electrons which carry heat or electricity through the metal) all save mercury, which is a liquid at room temperature.
The transition elements do not react vigorously with oxygen or water for they are not very reactive, but some may corrode very slowly. This makes them very useful for building materials and are mixed together to form alloys.
The transition metals are also very colourful this is because of the arrangement of atoms in their atoms. For the transition metals are between groups 2 and 3 their inner shells (either second or third inner shell) is only partially filled. Because of this the elements are brightly coloured and can be used as catalysts.