Question

1. fill-in-the-blanks:

a)the electron arrangement in an atom is also called
_________________________
b) _________________orbital gets filled with electrons just before 3d orbital starts
filling up
c) the electrons in the outermost (highest) principal energy level of an atom
are called
____________________electrons

Explanation:

Part (a)

In the context of atomic structure, the arrangement of electrons in an atom, which follows specific rules like the Aufbau principle, Pauli exclusion principle, and Hund's rule, is known as the electron configuration. This configuration describes how electrons are distributed among the atomic orbitals (such as s, p, d, f orbitals) in different energy levels.

According to the Aufbau principle (the order of filling atomic orbitals based on increasing energy), the energy of the 4s orbital is lower than that of the 3d orbital. So, electrons fill the 4s orbital first, and once the 4s orbital is filled (with 2 electrons), the filling of the 3d orbital starts. So the orbital that gets filled just before the 3d orbital is the 4s orbital.

By definition, the electrons present in the outermost (highest) principal energy level of an atom are called valence electrons. These valence electrons are responsible for the chemical properties of an element as they participate in chemical bonding (like forming ionic or covalent bonds) with other atoms.

Answer:

electron configuration

Part (b)