How do periodic trends impact chemical reactivity?

Periodic trends significantly influence chemical reactivity by affecting atomic size, ionisation energy, electronegativity, and electron affinity.

Periodic trends refer to the patterns that emerge when elements are arranged in order of increasing atomic number. These trends are a result of the arrangement of electrons in atoms, which in turn influences the chemical reactivity of the elements.

The atomic size, or atomic radius, is one of the key factors that impact chemical reactivity. As you move down a group in the periodic table, the atomic size increases due to the addition of energy levels. This increase in size reduces the attraction between the nucleus and the outermost electrons, making it easier for the atom to lose electrons and react with other elements. Conversely, as you move across a period from left to right, the atomic size decreases. This is because the number of protons in the nucleus increases, pulling the electrons closer and making it harder for the atom to lose electrons, thus reducing its reactivity.

Ionisation energy, the energy required to remove an electron from an atom, also plays a crucial role in determining reactivity. Elements with low ionisation energies, such as those in Group 1 (alkali metals), are highly reactive because they can easily lose an electron to achieve a stable electron configuration. On the other hand, elements with high ionisation energies, such as those in Group 18 (noble gases), are generally unreactive because they already have a stable electron configuration.

Electronegativity and electron affinity are two other periodic trends that impact reactivity. Electronegativity is a measure of an atom's ability to attract shared electrons in a chemical bond. Elements with high electronegativities, such as fluorine, are highly reactive. Electron affinity is the energy change that occurs when an electron is added to a neutral atom. Elements with high electron affinities, such as the halogens, readily gain electrons and are therefore highly reactive.

In summary, periodic trends greatly influence the chemical reactivity of elements. Understanding these trends can help predict how different elements will behave in chemical reactions.