Atoms and Molecules: Definition, Structures & Examples

Let us start by looking at things around us in our rooms, and we might see a table, chair, a book or maybe a laptop? All of these things inside your room are matter and are made up of atoms and molecules. Atoms make up everything you can see, touch, smell, feel, and taste. 

Atoms are the fundamental constituents of all substances. Covalent (chemical) bonds bind one or more atoms together to form molecules. In this article, we will learn more about atoms and molecules and how are they formed with some examples.

What are Atoms?

Atoms can be considered the basic unit of matter on a micro-level, creating a substance by combining with many other atoms. Similarly, how brick is the most fundamental substance in a building combined with other bricks to make the building or how a tiny grain of sand is nothing in itself but can create a whole dessert altogether when many of them combine. So, atoms are the basic building blocks of matter around us, and so the table, a chair and a laptop in our rooms are made up of atoms.

Atoms are considered small in size, and they have a size around \(1\) angstrom \(\left(10^{-10} \mathrm{~m}\right)\) or picometer \(\left(10^{-12} \mathrm{~m}\right)\), which is a thousand million times smaller than a metre; hence they are pretty small in size and are also not visible with our naked eyes. Humans discover (118) elements, and each of these elements has its atoms. So we have atoms of Hydrogen, Oxygen, Nitrogen and many other elements and each of them is different from the other in size, chemical and physical properties.

Structure of Atoms

Atoms earlier were considered to be indivisible. Even their name means something which can not be divided in greek, but after intense research work by many scientists, it was known that atoms are made of three subatomic particles called electrons, protons and neutrons. The protons and neutrons are concentrated in the centre of an atom, and the electrons revolve around the nucleus. All the mass of the atom is also concentrated in the atom’s nucleus.

Neil’s Bohr gave this kind of structure of the atom. We are currently following Schrodinger’s structure of the atom, which contains the theory of particle’s dual nature and the uncertainty principle. The structure of atoms given by humans has been corrected many times in history by many scientists and physicists like JJ Thomson, Ernest Rutherford, Neil Bohr and Erwin Schrodinger.

Dalton’s Postulate of Atoms

Dalton was amongst the very first persons who gave the theory of atoms. These postulates helped provide reasons for many ideas like the Law of conservation of mass, Dalton’s Postulate:

1. The atom is of tiny size and is not visible with our naked eyes.
2. The atom is indivisible.
3. Atom can neither be created nor can be destroyed.
4. The atoms of the same element are similar in all properties.
5. The atoms of different elements have different properties from each other.
6. The atoms combine in simple ratios to form compounds.
7. In chemical reactions, the only rearrangement of atoms takes place.

Limitations of Dalton’s Postulate

Few of Dalton’s postulates were proved to be wrong after intensive research as well,

1. Atoms are divisible into subatomic particles like protons, electrons and neutrons.
2. Isotopes and isobars of atoms are not accounted for in theory.
3. Few chemical compounds do not have simple whole-number ratios like \(\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}\).

Molecules

Molecules can be defined as the basic unit of compounds composed of more than one atom chemically bonded together, forming a pure substance with no net charge over it. Molecules are also divided into a compound molecule, a molecule of an element.

1. Molecule of Compound – A compound’s molecule comprises two or more different elements chemically bonded together and forming a compound. For example, A water molecule is a molecule of a compound where the molecule has two hydrogen atoms and one oxygen atom, two different elements, \(\mathrm{H}_{2} \mathrm{O}\).
2. Molecule of Element – A molecule of the element is defined as a molecule made up of only one atom chemically bonded together. For example, A molecule of oxygen gas is a molecule of the element as it has only one type of atom in it, and that is the oxygen atom, \(\mathrm{O}_{2}\).

Atomicity

The number of atoms present in the molecule of the compound or element is known as its atomicity.
The atomicity of oxygen gas \(\left(\mathrm{O}_{2}\right)\)  is two and is known as a diatomic molecule.
The atomicity of ozone gas \(\left(\mathrm{O}_{3}\right)\)  is three and is known as a triatomic molecule.
The atomicity of phosphorous \(\left(\mathrm{P}_{4}\right)\) is four and is known as a tetratomic molecule and so on.

Difference Between Atoms and Molecules

Atoms are the smallest unit of an element, whereas a molecule is the smallest unit of a compound. Also, a molecule is formed when two or more atoms are chemically combined. Let us understand this concept with the help of an example as well.

An atom is the smallest particle of an element; for example, in Nitrogen gas \(\left(\mathrm{N}_{2}\right),\) the smallest repeating unit is the Nitrogen atom, whereas the \(\mathrm{N}_{2}\,\) is the molecule of Nitrogen gas as it is made up of two atoms together. Also, giving another example, a water molecule is the smallest unit of water which \(\mathrm{H}_{2} \mathrm{O}\) and the molecule of water is made up of two hydrogen atoms and one oxygen atom together.

FAQs

Q.1. What is the structure of a Molecule?
Ans: Atoms are made of three subatomic particles called electrons, protons and neutrons. The protons and neutrons are concentrated in the centre of an atom, and the electrons revolve around the nucleus. All the mass of the atom is also concentrated in the nucleus of the atom. This kind of structure of the atom was given by Neils Bohr. We are currently following Schrodinger’s structure of the atom, which contains the theory of particle’s dual nature and the uncertainty principle.

Q.2. What are the types of molecules?
Ans: Molecules are also divided as a molecule of the compound, a molecule of an element.
1. Molecule of Compound – A molecule of a compound is made up of two or more different elements chemically bonded together and forming a compound. For example, A water molecule is a molecule of a compound where the molecule has two hydrogen atoms and one oxygen atom, two different elements, \(\mathrm{H}_{2} \mathrm{O}\).
2. Molecule of Element – A molecule of the element is defined as a molecule made up of only one kind of atom chemically bonded together. For example, A molecule of oxygen gas is a molecule of the element as it has only one type of atom in it, and that is the oxygen atom, \(\left(\mathrm{O}_{2}\right)\).

Q.3. What are Atoms?
Ans: Atoms are the basic building blocks of matter around us from which matter is made. Atoms can be considered the basic unit of matter on a micro-level, creating a substance by combining with many similar atoms. Just like how in a building, brick is the most fundamental substance combining with other bricks to make the building or how a tiny grain of sand is nothing in itself but can create a whole dessert altogether when many of them combine.

Q.4. What is Molecule?
Ans: Molecules can be defined as the basic unit of compounds composed of more than one atom chemically bonded together, forming a pure substance with no net charge over it. Molecules are also divided as a molecule of the compound, a molecule of an element.

Q.5. What is the difference between Atoms and Molecules?
Ans: Atoms are defined as the smallest unit of an element, whereas a molecule is the smallest unit of a compound. Also, a molecule is formed when two or more atoms are chemically combined together.