The key difference between atomic spectroscopy and molecular spectroscopy is that the atomic spectroscopy refers to the study of the electromagnetic radiation absorbed and emitted by atoms whereas the molecular spectroscopy refers to the study of the electromagnetic radiation absorbed and emitted by molecules.
An electromagnetic wave is consisting of an electric field and magnetic field oscillating perpendicular to each other. Thus, the full range of electromagnetic radiation wavelengths is what we call the electromagnetic spectrum. In spectroscopy experiments, we use electromagnetic radiation of specific wavelengths to analyze a sample. There, we let the electromagnetic radiation to pass through our sample which contains the chemical species of interest.
CONTENTS
1. Overview and Key Difference
2. What is Atomic Spectroscopy
3. What is Molecular Spectroscopy
4. Side by Side Comparison – Atomic Spectroscopy vs Molecular Spectroscopy in Tabular Form
5. Summary
What is Atomic Spectroscopy?
Atomic spectroscopy refers to the study of the electromagnetic radiation absorbed and emitted by atoms. Since chemical elements have unique spectra, we can use this technique to analyze the composition of elements in a sample.
Electrons are in certain energy levels of an atom. We call these energy levels as atomic orbitals. These energy levels are quantized rather than being continuous. The electrons in the atomic orbitals can move from one energy level to another by either absorbing or releasing the energy they have. However, the energy that the electron absorbs or emits should equal the energy difference between the two energy levels (between which the electron is going to move).
Figure 01: Electromagnetic Spectrum
Since each and every chemical element has a unique number of electrons at their ground state, an atom will absorb or release energy in a pattern unique to its elemental identity. Therefore, they will absorb/emit photons in a correspondingly unique pattern. Then we can determine the elemental composition of a sample by measuring the changes in light wavelength and light intensity.
What is Molecular Spectroscopy?
Molecular spectroscopy refers to the study of the electromagnetic radiation absorbed and emitted by molecules. The molecules in the sample can absorb some wavelengths that we pass through the sample and can move to a higher energy state from the existing lower energy state. The sample will absorb particular wavelengths but not all, depending on the chemical composition of the sample. Therefore, the non-absorbed wavelengths pass on through the sample. Then, depending on the absorbed wavelengths and the intensity of absorption, we can determine the nature of the energetic transitions that a molecule is able to undergo, and therefore, gather the information about its structure.
What is the Difference Between Atomic Spectroscopy and Molecular Spectroscopy?
Atomic and molecular spectroscopy are two techniques in which we use an electromagnetic radiation source in order to determine the composition of a sample. However, the key difference between atomic spectroscopy and molecular spectroscopy is that the atomic spectroscopy refers to the study of the electromagnetic radiation absorbed and emitted by atoms whereas the molecular spectroscopy refers to the study of the electromagnetic radiation absorbed and emitted by molecules. Therefore, atomic spectroscopy determines the type of atoms present in a given sample while molecular spectroscopy determines the structure of molecules present in a given sample.
The below infographic presents the difference between atomic spectroscopy and molecular spectroscopy in tabular form.
Summary – Atomic Spectroscopy vs Molecular Spectroscopy
Spectroscopy is an important technique in analytical chemistry that we use to determine the chemical composition of a sample. Here, atomic and molecular spectroscopy are such two techniques. However, there is some difference between atomic spectroscopy and molecular spectroscopy. The key difference between atomic spectroscopy and molecular spectroscopy is that the atomic spectroscopy refers to the study of the electromagnetic radiation absorbed and emitted by atoms whereas the molecular spectroscopy refers to the study of the electromagnetic radiation absorbed and emitted by molecules.
Reference:
1. Libretexts. “4.1: Introduction to Molecular Spectroscopy.” Chemistry LibreTexts, Libretexts, 11 Apr. 2017. Available here
2. “Atomic Spectroscopy.” Wikipedia, Wikimedia Foundation, 12 Sept. 2018. Available here
Image Courtesy:
1.”EM spectrum” (CC BY-SA 3.0) via Commons Wikimedia