Question

How do you define a valence electron? How do you determine the valence number of an atom?

Answer 1

Except for bunches 3–12 (the progress metals), the unit digit of the gathering number distinguishes the number of valence electrons related to an impartial molecule of a component recorded under that specific section.

Complete step by step solution:
While everything on our planet is composed of individual molecules and components, the contrasts among items and species lie in the capacity for components to join with different components. The valency of a component, which is dictated by the number of electrons in its peripheral shell, gauges its similarity with different components. While components with eight electrons on their external shells are viewed as steady, components with simply six or seven will in general shape a multi-particle bond with components that just have a couple of electrons on their external shell.
Locate the nuclear number of the component to decide the number of electrons on its external shell. For instance, the Potassium (K) component has a nuclear number of 19. Subsequently, it will have one electron on its external shell since it has two electrons in its deepest shell, eight on its subsequent shell, eight on its third shell, and just one on its external fourth shell $\left( {2{\text{ }} + {\text{ }}8{\text{ }} + {\text{ }}8{\text{ }} + {\text{ }}1{\text{ }} = {\text{ }}19} \right).$
Take away the number of electrons on the furthest shell of the iota by eight to get the number of valence electrons. For instance, if the furthest shell of Potassium contains just a single electron, the quantity of valence electrons is seven $\left( {8{\text{ }} - {\text{ }}1{\text{ }} = {\text{ }}7} \right)$ .

Note:
Valence electrons are the electrons in the external energy level of a particle that can partake in collaborations with different iotas. Valence electrons are by and large the electrons that are farthest from the core.