Periodicity

• Periodicity refers to the repeating pattern seen in the properties of elements across periods in the periodic table.
• This phenomenon occurs due to the cyclical pattern of electron configuration as you move across each period.
• Going from left to right across a period, the atomic number increases by one for each successive element which results in a regular pattern in the properties of elements.
• One example of periodicity is the pattern of ionisation energies. Ionisation energy increases across a period until reaching a noble gas, then dramatically decreases at the start of a new period.
• A second period trend is seen in atomic radius, which decreases across a period from left to right. This is due to the increasing attractive force between electrons and the nucleus as we add more protons to the nucleus.
• The pattern of metallic and non-metallic character also shows periodicity. Metals generally occupy the left and centre of the table, and non-metals appear on the right.
• Metallic character decreases across a period while non-metallic character increases, this due to the increase of electronegativity across the period.
• Electronegativity refers to an atom’s ability to attract shared electrons, and it generally increases as you move across a period and decreases as you go down a group.
• The periodicity of reactivity varies, depending on whether we are discussing metals or non-metals. Metallic reactivity decreases across a period, while non-metallic reactivity increases.
• Elements in the same group share similar chemical properties. This is due to them all having the same number of outer shell electrons, they also show trends in physical properties such as boiling point.
• The elements are arranged in the Periodic Table in order of increasing atomic number, that is, the number of protons in an atom’s nucleus.
• The current form of the Periodic Table (known as the ‘long form’) was developed after the original one created by Dmitri Mendeleev in the 19th century, most notably to incorporate the Noble Gases and the transition metals.
• Understanding these trends in periodicity helps to predict how an element will behave in a chemical reaction.