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← 🧪 Chemistry · usually met in Std 7-12

Atoms and molecules

The atom is the smallest piece of an element that is still that element. Join atoms together and you have a molecule — and nearly everything around you is molecules.

An atom (carbon) 6p 6n nucleus: protons + neutrons electrons — chemistry happens here Almost all of it is empty space. The proton count is what makes it carbon and not anything else. A molecule (water) O H H The bend is the point: it gives water a positive end and a negative end.
Drawn for Star Student.

An atom has a tiny dense nucleus of protons and neutrons, with electrons occupying the space around it. The number of protons decides which element it is: one proton is hydrogen, six is carbon, seventy-nine is gold, and changing that number changes the element itself. Electrons are what chemistry is mostly about, because bonding is atoms sharing or transferring them.

A molecule is two or more atoms bonded together. Two hydrogen atoms with one oxygen make water, and water behaves nothing like either gas it came from — that is the point of chemistry. The scale is hard to hold in your head: a single drop of water contains more molecules than there are drops of water in all the lakes of India.

Worth knowing

  • An atom is almost entirely empty space. If the nucleus were a marble on the halfway line of a cricket ground, the electrons would be out past the boundary.
  • The idea goes back to Kanada in ancient India and to Democritus in Greece, long before anything could be measured.
  • Isotopes are atoms of the same element with different numbers of neutrons — same chemistry, different mass.

Want to see it moving? Search YouTube for “Atoms and molecules” ↗ — we send you to the search rather than to one video, because a link to one video eventually rots.

See also

🧪 The periodic table🧪 Chemical reactions🧪 States of matter

🧭 Do not take our word for it

This entry was written for Star Student in our own words — it is a summary, not a source. Here is where the people who actually hold these facts keep them. Go and check.

Your own textbook ↗Balbharati publishes the textbooks free to read online. Your chapter is the thing to check first — an encyclopedia is a summary, and the syllabus is the syllabus.

Last gone through: 1 October 2026 · How these entries are written

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