The Periodic Table

The Periodic Table

Development of the Periodic Table

• The Periodic Table was first devised by Dmitri Mendeleev in the 19th century.
• Mendeleev arranged elements in order of increasing atomic weight, and grouped elements with similar properties together.
• He left gaps for elements that had not yet been discovered, accurately predicting their properties.

Modern Periodic Table

• The modern Periodic Table is arranged in order of increasing atomic number (number of protons).
• The rows of the Periodic Table are called periods and the columns are called groups.
• The Periodic Table is divided into blocks - s, p, d and f - which refers to the type of orbital that the outermost electrons occupy.

Group Properties

• Elements in the same group have similar chemical properties because they have the same number of electrons in their outer shell.
• The vertical columns (Groups 1 to 8) represent elements that share the same outer-shell electron configuration.
• For example, Group 1 elements are called alkali metals, are very reactive and have 1 electron in their outer shell.

Period Properties

• Elements in the same period have the same number of electron shells or energy levels.
• Periods represent a complete sequence of electron shells. Each period corresponds to a new outer energy level being filled.
• For example, Period 3 elements all have three electron shells.

Groups on the Periodic Table

• Group 0 elements are called the Noble Gases. They have full outer electron shells making them very stable and unreactive.
• Group 7 elements are called the Halogens. They have seven electrons in their outer shell.
• The transition metals are found in the centre of the table. They often form coloured compounds and can have more than one ion.

Metals and Non-metals

• The left side of the Periodic Table consists of metals which have properties such as high melting and boiling points, are good conductors of heat and electricity, and are malleable.
• The right side of the Periodic Table consists of non-metals with properties such as low melting and boiling points, poor conductors of heat and electricity and are brittle.
• The stair-step line on the Periodic Table separates metals from non-metals. Elements on this line are semi-metals or metalloids.

Relative Atomic mass

• The mass number shown in each element box on the Periodic Table is the relative atomic mass (Ar). This takes into account the abundances of the naturally occurring isotopes of each element.