Difference Between Atom and Molecule

Main Difference – Atom vs Molecule

Atoms are the building blocks of molecules. Everything around us is made up of either molecules or atoms. In this article, we will discuss the difference between atom and molecule with regard to their chemical as well as physical properties. The main difference between atom and molecule is their size; an atom is the smallest component of an element whereas a molecule is made of two or more atoms. 

This article explores,

1. What is an Atom
     – Definition, Structure, Properties
2. What is a Molecule
     – Definition, Structure, Ionic Bonds, Covalent Bonds
3. What is the difference between Atom and Molecule

What are Atoms

An atom is defined as the smallest component of an element, which shows the chemical properties that relate to the particular element. Atoms can further be broken down into protons, neutrons, and electrons; however, these subatomic particles do not display the chemical characteristics of the element when they are separated. An atom of a certain element contains a fixed number of electrons, protons, and neutrons most of the time.

Carbon atoms contain 6 protons, 6 electrons, and 6 neutrons. This combination of subatomic particles is unique for ¹²C. However, some elements have isotopes. Carbon is one such element. The isotopes differ in their number of neutrons. This gives rise to radioactivity.

The mass of an atom is mainly determined by the protons and neutrons as electrons have negligible mass compared to them. Protons have a positive charge while electrons and neutrons have negative and neutral charges, respectively. The nucleus of an atom is composed of protons which clung together by neutral neutrons to overcome the repulsive forces of like charges. Electrons can be randomly found in pathways called orbitals surrounding the nucleus.

The atom cannot be separated into subatomic particles by chemical reactions but the separation is possible by nuclear reactions.

Figure 1: Structure of Atom

What are Molecules

Molecules are made of two or more atoms coming together to share electrons or exchange electrons. These atoms in molecules are held together by different type of bonds. Only the electrons in the outer shell of an atom are involved in bonding.

Ionic Bonds

Electrons are exchanged between atoms. The atom which releases an electron gains a positive charge whereas the atom which gains the electron, is negatively charged. The attraction between these oppositely charged ions is called an ionic bond.

Figure 2: Example of Ionic Bonding

The example of sodium chloride shows that one electron from Na is transferred onto Cl, leaving a positive charge on Na. Cl becomes negatively charged. Due to the attraction between these two oppositely charged ions, NaCl is considered as an ionic salt.

Covalent Bonds

Covalent bonds are formed by sharing electrons between two atoms. Therefore, the shared pair of electrons belongs to both the atoms involved. Covalent bonding can give rise not only to single bonds but also to multiple bonds such as double and triple bonds. (Read: How are Covalent Bonds Formed)

Figure 3: Example of Covalent Bonding

Read More: Difference Between Covalent and Ionic Bonds

Difference Between Atom and Molecule

Atom: Atoms are the building blocks of molecules. The smallest singular entity which displays the chemical properties of the corresponding element.

Molecule: Molecules are made of two or more elements. They do not display the individual properties of the constituent elements.

Components

Atom: Atoms consist of subatomic particles: protons, electrons, neutrons.

Molecule: Molecules consist of more than two atoms which can be either of the same element or of different elements.

Stability

Atom: Atoms are not stable alone, and make chemical bonds with other atoms to become stable.

Molecule: Molecules are stable alone. 

Separation 

Atom: Atoms cannot be separated into subatomic particles by chemical reactions. Separation is only possible by nuclear reactions.

Molecule: Molecules can be separated into atoms by chemical reactions.

Conclusion

Atoms and molecules are the founding entities of the universe. As we discussed earlier, atoms make up molecules. However, chemical properties of atoms are not often retained when they form molecules. For example, Na is a highly reactive metal whereas Cl is a toxic gas. However, table salt (NaCl) is neither a metal nor toxic. This indicates that the chemical properties of atoms are changed when they become molecules.

Molecules can be separated into their constituent atoms by chemical means. This is not possible with atoms. Atoms can be separated into subatomic particles by nuclear reactions.

Molecules can exist by themselves and are often stable. However, this is not the case of atoms. Only atoms that have noble gas configuration are able to be stable by themselves.  Argon, helium, krypton etc.  are some examples of such atoms. The reason for their stability is that they have reached the maximum number of electrons in their outer shells. Hence, they don’t display any charge. However, atoms which don’t have this kind of stability come together to either share or transfer electrons to make molecules and become stable.

Reference:
1.”What is an Atom?” LiveScience. Purch, n.d. Web. 15 Feb. 2017.
2.”What is molecule? – Definition from WhatIs.com.” WhatIs.com. N.p., n.d. Web. 15 Feb. 2017.

Image Courtesy:
1.”Atom diagram” By The original uploader was Fastfission at English Wikipedia – Transferred from en.wikipedia to Commons by Teratornis using CommonsHelper. (CC BY-SA 3.0) via Commons Wikimedia
2. “207 Ionic Bonding-01” By OpenStax College – Anatomy & Physiology, Connexions Web site.(CC BY 3.0) via Commons Wikimedia
3. “Figure 02 01 08” By CNX OpenStax – (CC BY 4.0) via Commons Wikimedia