Periodic Table

Key Stage 3

Meaning

The Periodic Table is a chart listing all the known elements arranged in order of Atomic Number and in columns of elements with similar properties.

About The Periodic Table

The modern Periodic Table is based on an earlier Periodic Table made by a scientist called Mendeleev. Others had tried to arrange all the elements before, but Mendeleev was the first to correctly arrange it by both Relative Atomic Mass and chemical properties with gaps where elements were later discovered.

The modern Periodic Table is only slightly different and is arranged by Atomic Number and chemical properties.

The columns of the Periodic Table are called groups.

The rows of the Periodic Table are called periods.

Groups

The elements are arranged groups of similar chemical properties.

Elements have similar chemical properties when they have the same number of electrons in the Outer Shell.

Trends within groups

The chemical properties of elements within a group are similar. However, the reactivity within a group changes as you move up or down the periods.

Group 1: The Alkali Metals all react strongly with water. The reactivity increases as you go down the group.
Group 2: The Alkali Earth Metals all react strongly with steam and acids. The reactivity increases as you go down the group.
Group 7: The Halogens all act as bleaching agents and kill bacteria. The reactivity decreases as you go down the group.
Group 0: The Noble Gases are all inert (unreactive).

The physical properties of elements within a group are similar. However, the property changes gradually as you move down the group.

Periods

The periods are arranged by the number of Electron Shells.

Trends within Periods

The chemical and physical properties of elements change as you move along a period.

Period 2 Melting Points	Period 3 Melting Points

There is a trend in the Melting Points as you move along the period.	A similar trend can be seen in the next period.

Periodic Table Song

Linked Periodic Table

Key Stage 4

Meaning

The Periodic Table is a chart listing all the known elements arranged in order of Atomic Number and in columns of elements with similar properties.

About The Periodic Table

The modern Periodic Table has the elements arranged by Atomic Number and chemical properties.

Elements on the Periodic Table are written with their Chemical Symbols and two numbers representing their Relative Atomic Mass and Atomic Number.

The Relative Atomic Masses on the Periodic Table are an average atomic mass of different isotopes of the same element.

The position of an element in the Periodic Table is a result of the Electronic Structure of the element, which itself is due to the Atomic Number of the element.

The elements in each column of the Periodic Table all have the same number of electrons in the Outer Shell (except Helium in the Noble Gases) which causes them all to have the same chemical properties. These columns are known as groups.

The elements in each row of the Periodic Table all have the same number of Electron Shells. These rows are called periods.

History of the Periodic Table

Scientists always try to look for patterns to help arrange complicated problems. Many different elements had been discovered so scientists wanted to arrange them based on patterns they noticed. Some scientists arranged them by patterns in chemical properties while others tried to arrange them by patterns in physical properties like melting point or relative atomic mass.

In 1808 a scientist called John Dalton, who created the Dalton Model of the atom, arranged elements by their relative atomic mass.

In 1864 a scientist called John Newlands arranged elements by relative atomic mass but because he noticed that ever 8th element had similar chemical properties he arranged them into what he called 'octaves'. However, he had not taken into account the possibility that some elements had not been discovered, so he placed some elements into the wrong groups just to fit the pattern he thought he had seen.

In 1869 Mendeleev was the first to place gaps where the elements did not fit the pattern but still arranged them by both their chemical properties and relative atomic mass. This enabled Mendeleev to predict the existence of elements that had not yet been discovered.

Mendeleev's Periodic Table was proven (nearly) correct when new elements were discovered that fit in the the gaps he had left. This ability of his table to predict the properties of new elements was what convinced other scientists his Periodic Table was (nearly) correct.

There were some problems with Mendeleev's Periodic Table that kept scientists skeptical of it. One such problem was that Argon has a greater relative atomic mass than Potassium which would put Argon in the Alkali Metals.

Once the structure of the atom was investigated by physicists in the early 1900s it was discovered how to correct Mendeleev's Periodic Table by ordering the elements by atomic number instead of relative atomic mass. This produced the modern Periodic Table.