Can atoms be seen with the naked eye?

No, atoms are too small to be seen with the naked eye. They require powerful microscopes to be observed.

Are all molecules made up of different types of atoms?

No, some molecules, like O₂, are made up of the same type of atoms.

Is an atom the smallest particle in the universe?

No, atoms are made up of smaller particles called protons, neutrons, and electrons. There are also particles smaller than these, such as quarks and leptons.

Atoms and Molecules: Definition, Size, And Examples

Atoms and molecules: Atoms and molecules are the basic building blocks of matter. Understanding them is fundamental in chemistry and other sciences.

ByAtul Rawal

Jul 23, 2024, 12:28 IST

Definition, Size, And Examples of Atoms and Molecules

What is Atom and Molecule? Atoms and molecules are an important part of science and the building blocks of matter. Understanding them is the foundation for understanding all branches of science. Students often confuse the terms atoms, molecules, elements, and compounds. Here, we will elaborate on atoms and molecules to bring better clarity to students and make the concept more understandable.

What is Atom?

An atom is the smallest unit of an element that retains the properties of that element. It is made up of a nucleus containing protons and neutrons, with electrons orbiting around the nucleus.

What is the Size of an Atom?

Atoms are extremely small. Their size is measured in picometres (pm) or nanometres (nm). Typically, an atom is about 0.1 to 0.5 nanometres in diameter.

Relative Sizes of Atoms

Atoms vary in size depending on the element. Hydrogen atoms are the smallest, while atoms of larger elements like uranium are much bigger. Atomic radius is generally measured in nanometres. 1m=10⁹nm. The atomic radius increases from right to left in periodic table of elements.

Element	Symbol	Atomic Radius (nm)	Example Comparison
Hydrogen	H	0.37	Smaller than the width of a human hair (average 80,000 nm)
Helium	He	0.31	Smaller than the width of a human hair
Carbon	C	0.77	Slightly larger than a single-walled carbon nanotube (0.4-1.4 nm)
Nitrogen	N	0.75	Similar size to a Carbon atom
Oxygen	O	0.66	Slightly smaller than a Carbon atom
Sodium	Na	1.86	Larger than a Carbon atom, about the size of a potassium ion (K+)
Magnesium	Mg	1.6	Smaller than a Sodium atom
Aluminum	Al	1.89	Similar size to a Sodium atom
Chlorine	Cl	0.99	Larger than a Carbon atom, but smaller than a Sodium atom
Argon	Ar	0.98	Similar size to a Chlorine atom
Iron	Fe	1.26	Larger than a Carbon atom, but smaller than a Sodium atom
Gold	Au	0.144	Much smaller than a typical atom due to metallic bonding, about the size of a Hydrogen atom
Uranium	U	0.138	Similar size to Gold atom due to metallic bonding

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What are Atoms made of?

Atoms consist of three main particles:

Protons: Positively charged particles in the nucleus.
Neutrons: Neutral particles in the nucleus.
Electrons: Negatively charged particles orbiting the nucleus.

What is Atomic Mass?

Atomic mass is the mass of an atom, usually measured in atomic mass units (amu). It is roughly equal to the sum of the number of protons and neutrons in the atom's nucleus.

Salient Features of Dalton’s Atomic Theory

Atoms are indivisible particles that cannot be created or destroyed.
Atoms of a given element are identical in mass and properties.
Atoms of different elements have different masses and properties.
Atoms combine in simple whole numbers to form compounds.
Chemical reactions involve the rearrangement of atoms.

What is a Molecule?

A molecule is a group of two or more atoms bonded together. Molecules can consist of atoms of the same element or different elements. For example:

Oxygen (O₂): Two oxygen atoms bonded together.
Water (H₂O): Two hydrogen atoms and one oxygen atom bonded together.
Carbon Dioxide (CO₂): One carbon atom and two oxygen atoms bonded together.

Forces between Atoms and Molecules

Atoms and molecules are held together by different types of forces:

Covalent Bonds: Strong bonds where atoms share electrons.
Ionic Bonds: Bonds formed through the transfer of electrons from one atom to another.
Van der Waals Forces: Weak attractions between molecules.

Atom vs Element vs Molecule vs Compound

The table below explains the differences between the atom, element, molecules and a compound. Check and clear all your doubts related to these four.

Feature	Atom	Element	Molecule	Compound
Definition	The fundamental building block of matter	Pure substance composed of only one type of atom	Two or more atoms chemically bonded together	A substance composed of two or more different elements chemically bonded together in a fixed ratio
Examples	Hydrogen (H), Helium (He)	Iron (Fe), Oxygen (O)	Water (H₂O), Oxygen gas (O₂)	Carbon dioxide (CO₂), Table salt (NaCl)
Composition	Protons, neutrons, and electrons	One type of atom	Two or more atoms of the same or different elements	Two or more different elements
Stability	Generally stable	Can be stable or unstable	Generally stable	Generally stable