The smallest unit of an element that retains the element's chemical identity, made of protons, neutrons and electrons.
Practise Atomic Structure & Periodicity All Atomic Structure & Periodicity topics
An atom is the smallest particle of an element that keeps that element's chemical identity. It consists of a tiny, dense nucleus of protons and neutrons surrounded by a cloud of electrons. Nearly all of the mass lies in the nucleus, yet the electrons govern bonding and almost all chemical behaviour. An atom is electrically neutral when its proton and electron counts are equal, and its diameter is roughly 10^-10 m, or 0.1 nm. Because of this tiny scale, a line of a few million atoms would span only about a millimetre.
Key ideas: An atom has a tiny dense nucleus (about 10^-15 m across) surrounded by electrons, with the whole atom about 10^-10 m (1 angstrom) wide, so it is mostly empty space. Nearly all the mass sits in the nucleus. The atom is electrically neutral because protons equal electrons. Chemical behavior is set by the electrons, while identity is set by the proton count.
Common mistakes and connections: A common error is picturing the atom as a solar system with electrons in fixed orbits, which later models replace with orbitals. Another is thinking atoms are indivisible, which is false since they contain subatomic particles. Atoms connect to isotopes, ions (charged atoms) and the mole concept.
A carbon atom drawn as Bohr shells: 6 electrons orbit a tiny nucleus holding 6 protons and neutrons, 2 in the inner shell and 4 in the outer. The interactive lesson shows this as a live animation or chart.
A neutral carbon atom contains 6 protons, usually 6 neutrons and 6 electrons, giving a mass of about 12 atomic mass units.
The smallest unit of an element that retains the element's chemical identity, made of protons, neutrons and electrons.
Atom is a beginner topic in Atomic Structure & Periodicity. It needs no earlier chemistry lessons and is a good starting point.
Study these earlier topics in Atomic Structure & Periodicity first: Matter.
The next topics in Atomic Structure & Periodicity are Element and Compound.
Yes. The interactive lesson includes a self-check question on Atom, and the Atomic Structure & Periodicity quiz draws on every topic in this area.
Atom is topic 2 of 115 in Atomic Structure & Periodicity.