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⚛️ Atoms, Elements, and Compounds

From a single atom to the periodic table to water itself — learn how elements and compounds build every substance in the universe.

lessons

~15 min

to learn

🔬 Science

subject

Teens

level

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What you’ll learn

AtomsUnderstand that atoms are the building blocks of matter and name their main parts.An atom is the tiny building block of all matter. It has a nucleus of protons and neutrons with electrons moving around the outside. The number of protons decides which element the atom is.
ElementsDefine an element and locate elements and their symbols on the periodic table.An element is a substance made of only one kind of atom, like gold, oxygen, or iron, and cannot be split into anything simpler. All the known elements, about 118 of them, are arranged on the periodic table with their own symbols.
CompoundsDefine a compound and tell elements from compounds.A compound forms when atoms of different elements bond together in a fixed ratio, like water (H₂O) or salt (NaCl). A compound behaves nothing like the elements it is made from. The key difference from an element is that a compound joins different elements together.

Questions this course answers

What is an atom?

An atom is the tiny building block of all matter — so small that millions could fit across a single hair.

Which part of an atom decides which element it is?

The number of protons in the nucleus decides which element an atom is.

What is an element?

An element is a substance made of just one kind of atom and cannot be broken into anything simpler.

What is the periodic table?

The periodic table is a chart of about 118 known elements, each with its own symbol like O, Fe, or Au.

Water is H₂O. What kind of substance is it?

Water is a compound — atoms of two different elements, hydrogen and oxygen, bonded together as H₂O.

Which of these is a compound, not an element?

Salt (NaCl) is a compound because it is made of two different elements, sodium and chlorine, bonded together.

Grounded in trusted sources

Royal Society of Chemistry
BBC Bitesize
Britannica
American Chemical Society

Every Wunder lesson is built from real, reputable sources — never invented.

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