To calculate the number of electrons in an atom from its atomic number and valence shell configuration, you need to consider the electron configuration and the periodic table.
The electron configuration of an atom represents the distribution of electrons into different energy levels, subshells, and orbitals within an atom. It follows a specific pattern based on the Aufbau principle, which states that electrons fill the lowest energy levels first before moving to higher energy levels.
Here's a general process to determine the number of electrons:
Determine the atomic number (Z) of the element. The atomic number represents the number of protons in the nucleus and also the number of electrons in a neutral atom.
Identify the element's position in the periodic table to determine the general electron configuration pattern. The periodic table is organized based on electron configuration trends.
Identify the valence shell, which is the outermost electron shell. The valence shell determines the atom's chemical behavior and the number of valence electrons.
Count the number of electrons that occupy the valence shell. For main group elements (s and p block elements), the valence electrons are the electrons in the outermost s and p orbitals. For transition metals (d block elements), the valence electrons are typically the electrons in the outermost s and d orbitals.
Keep in mind that there may be exceptions or variations to the electron configuration pattern for some elements. However, this general approach will give you a good estimate of the number of electrons based on the atomic number and valence shell configuration.