Atom and molecule are the two terms that come to our minds when we think of the composition of an element or a compound. Atom is the smallest particle of an element that may or may not exist independently. On the other hand, a molecule is a combination of two or more atoms that are held together by a bond. It can exist freely in nature. In this article, we will see the actual difference between atom and molecule.
Atoms are spherical in shape while molecules can have linear, angular, triangular shapes. Atoms are highly reactive and take part in chemical reactions. On the other hand, molecules are quite stable and don’t take part in chemical reactions.
The matter is something that has some mass and occupies some space. And the matter is composed of atoms and molecules. From pen to paper, from chalk to blackboard, from a brick to a home everything is made up of atoms. Atoms are everywhere. Atoms are such small entities that they are not visible to naked eyes nor to the microscope.
Atom vs Molecule
Let’s analyze the differences between atom and molecule through the following table.
| Basis | Atom | Molecule |
| Definition | The most fundamental and smallest part of an element that can exist. | Formed when two or more atoms combine together. |
| Made up of | Made up of electrons, protons, and neutrons. | Made up of two or more atoms of the same kind or different kind. |
| Existence | Atoms may or may not exist independently. | Molecules exist in a free state. |
| Reactivity | They are highly reactive except for the noble gases. | They are not reactive. |
| Type of bond | They have a nuclear bond. | They have a covalent bond. |
| Shape | They are spherical in shape. | They may have a triangular, linear, or angular shape depending upon the arrangement of atoms. |
| Visibility | They are neither visible to naked eyes nor to a magnifying microscope. | They are not visible to naked eyes but are visible through a magnifying microscope. |
| Example | Hydrogen – H Oxygen – O Phosphorous – P |
Water – H2O Oxygen – O2 Phosphorous – P4 |
| Size | They are small in size. | They are comparatively larger in size. |
What is an atom?
An atom is the smallest particle of an element that does not exist freely in nature but takes part in chemical reactions. The atoms of nobles gases can exist freely in nature. An atom is made up of a nucleus(protons, neutrons) and electrons. It is spherical in shape. The nucleus lies in the center of the atom and electrons revolve around the nucleus in fixed circular orbits known as shells.
Protons and neutrons lie inside the nucleus and both of them have nearly the same mass. The mass of a neutron is slightly greater than the mass of a proton. Neutrons and protons contribute majorly to the mass of atoms. The electrons are negatively charged while protons carry positive and neutrons are electrically neutral species. Since protons and neutrons lie inside the nucleus, the nucleus is also assumed to be positively charged.
Each atom possesses the properties of its element in which it is present. The physical and chemical properties of an element are the periodic function of its atomic number. The atomic number of an element is determined by the number of protons present inside the nucleus of that atom.
What is a molecule?
Molecule refers to the set of two or atoms that are held together by a bond. These two atoms can be of the same type or different type. A molecule can exist freely in nature. It is the smallest component of a compound.
The electrons of a molecule can interact among themselves, and a chemical bond is formed due to this interaction. Electrons are exchanged between the elements and a covalent bond is formed which helps in providing stability to the molecule as the octet of all the elements is completed.
The shape of a molecule can be linear, angular, triangular depending upon the spatial (in space) arrangement of atoms within the molecule. As a molecule is formed by the combination of atoms, the size of a molecule is greater than the atoms which form it.
Now you might ask a question, why do atoms form molecules? When an atom loses or gains electrons it acquires some charge. It is the tendency of every atom to make itself stable so in order to stabilize itself an atom shares its electrons with other atoms and forms a bond. Thus a molecule is formed.
People are often confused between molecules and ions, molecules and ions are different from each other with respect to the fact that molecules are electrically neutral while ions contain some charge.
Conclusion
From the above discussion, we have concluded that atoms and molecules both are an important part of matter. Atoms are the smallest particle of an element which takes part in a chemical reaction. Atoms can’t be further subdivided. They don’t exist independently in nature except for noble gases. Molecules are made up of two or more atoms and are the constituent component of a compound. Molecules can exist freely in nature. They are quite stable.
Author
Deepak Yadav
Aligarh Muslim University, Aligarh
