C1aL1 Elements and the Periodic Table

Key Words

Alkali metals - metals react with water to give alkaline solutions

Atomic Number - Number of protons

Atoms - the smallest particle that makes up an element

Elements - substance that consists of one type of atom

Groups - elements in the same column of the periodic table

Particles - small bits of a substance.

Periodic Table - the table in which elements are arranged to group them according to their properties.

Periods - rows in the periodic table, in which properties repeat themselves.

Grade E

Elements consist of one kind of atom only.  You cannot break an element down any further.  A molecule consists of two or more atoms, which can be of the same element, for example H₂.  Molecules can also be of different elements like carbon and hydrogen in methane, CH₄.  Elements combine with other elements to form compounds.

The earliest chemists were involved in futile attempts to make gold from all sorts of different things (to get gold you need a supernova explosion).  However they noticed patterns in reactions.  It was the Russian chemist Dimitri Mendeleev who was the first to set out the elements in a periodic table.  It was somewhat different to the modern period table we know today.

The columns are called groups, while the rows are called periods.

The first group is the alkali metals which all react with water to make an alkaline hydroxide solution.  Metals are on the left, while non-metals are on the right.

Although hydrogen is a gas, it can, under very high pressure, exist as a metal.

Grade C

The elements are arranged by increasing atomic number, which tells us how many protons there are.  Helium has an atomic number of two, and two protons.

Although Mendeleev found found that some elements had similar properties, there were a lot of gaps.  Gradually elements were discovered that filled the gaps.

Grade A

Mendeleev was not always sure where a particular element should go.  There were elements he moved from one group to another.  There were many that had not  been discovered.  However he mad a considerable contribution to our understanding of chemistry.