X-Ray Fluorescence Analytical Techniques - CNSTN : Centre ...

The energy of the emitted photon will be equal to the difference in energies between the
two orbitals occupied by the electron making the transition. Due to the fact that the energy
difference between two specific orbital shells, in a given element, is always the same (i.e.,
characteristic of a particular element), the photon emitted when an electron moves between
these two levels will always have the same energy. Therefore, by determining the energy
(wavelength) of the X-ray light (photons) emitted by a particular element, it is possible to
determine the identity of that element.
Figure I.1: A pictorial representation of X-ray fluorescence using a generic atom and
generic energy levels. This picture uses the Bohr model of atomic structure
and is not to scale.
III.4 Bohr’s Atomic Model
Bohr’s atomic model describes the structure of an atom as an atomic nucleus
surrounded by electron shells (Figure I.2). The positively charged nucleus is surrounded by
electrons that move within defined areas (shell). The differences in the strength of the
electron’s bonds to the atomic nucleus are very clear depending on the area or level they
occupy, i.e., they vary in their energy. When we talk about this, we refer to energy levels or
energy shells. This means that a clearly defined minimum amount of energy is required to
release an electron of the innermost shell from the atom. To release an electron of the second
innermost shell from the atom, a clearly defined minimum amount of energy is required that
is lower that that needed to release an innermost electron. An electron’s bond to an atom is
weaker the further away it is from the atom’s nucleus. The minimum amount of energy
required .to release an electron from an atom, and thus the energy with which it is bound to
the atom, is also referred to as the binding energy of the electron to the atom.