Key Concepts: The Periodic Table

The periodic table is a systematic arrangement of all known elements, based on their differing properties and similarities.
It’s organised in periods (rows) and groups (columns). There are 7 periods and 18 groups in total.
Each element on the table is given by its symbol, atomic number, and relative atomic mass. The atomic number is the unique number of protons in an atom of the element, whilst the relative atomic mass is an average mass taking into account all of the isotopes of that element.
Elements in the same group share similar characteristics, due to having the same number of electrons in their outer shell. This influences their behaviour when they react.
Moving across a period from left to right, each element gains one more proton and electron than the one before. This means elements in the same period have the same number of electron shells.
There is a clear pattern in electron configuration as you move across the periodic table. The first shell can hold up to 2 electrons, the second can hold up to 8, and the third can hold up to 8.
Elements on the left side of the table, the metals, have properties such as high melting/boiling points, they’re excellent conductors of heat and electricity, and are malleable and ductile.
The right side of the table is mostly composed of non-metals, which exhibit a large variety of properties, often contrasting those of metals.
Some elements, known as metalloids or semi-metals, have properties that are intermediary between those of metals and non-metals. These elements are located along the line that zigzags from Boron to Polonium.
The groups in the periodic table are numbered from 1 to 18. Group 1 elements are known as alkali metals, group 2 are alkaline earth metals, groups 3-12 are transition metals, group 17 are halogens and group 18 are noble gases.
Transition metals, which form coloured compounds and have variable oxidation states, while the Noble gases are inert due to their full electron shells.
In the modern periodic table, elements are arranged in order of increasing atomic number. This organisation method is known as the ‘Periodic Law’. Dmitri Mendeleev originally ordered elements by increasing atomic weight, but left gaps for undiscovered elements, predicting their properties with incredible accuracy.
The periodic table has continued to be expanded with the discovery of new synthetic elements, which are added to the seventh period. As of yet, no new period has been needed.