How do valence electrons determine an element’s reactivity?

Hint: In order to find how the valence electron will determine the element’s reactivity, we must first know what a valence electron is. Valence electron is an electron which is present in the outermost orbital or shell.

Complete step by step answer:
Let us first learn about the valence electron. Valence electron is an electron which is present in the outermost orbital or shell. The electrons which are present in the inner shells are called the core electrons. The valence electron is responsible for the interaction between the atoms and is also responsible for the formation of certain chemical bonds. In other words, we can say that the number of electrons lost or gained in order to attain a noble gas configuration.
- Metals from the Group I considered to be the most reactive element. The Group I metals will be having one valence electron. This electron is very easily lost from the metal to form a positive ion.
- Metals from Group II are considered to be somewhat less reactive. From Group II, two electrons will be easily lost to form a positive ion.
 So, we can say that the reactivity will decrease when we move down the group.
- A non-metal will attract an electron towards itself in order to attain a full valence shell. It can either share its electron to form a covalent bond or it can accept the electrons from other atoms to form an ionic bond. Within each group of the non-metals the reactivity will decrease from top to bottom. This is because the valence electrons are progressively at higher energies and the atoms will not gain much stability by gaining electrons.
- Oxygen is found to be more reactive compared to the halogen.

Note: We have to remember certain characteristics of the valence electrons such as
- It helps us to determine the electrical conductivity of an element.
- Depending on the valence electrons present we can determine the element present is metal, nonmetals or metalloids.