Atom - Definition, Examples, Quiz, FAQ, Trivia
Discover the building blocks of matter that make up everything around us
What is an Atom?
An atom is the smallest unit of matter that has the properties of an element. Everything around you—the air you breathe, the water you drink, the ground you walk on—is made of atoms!
Think of atoms as the building blocks of the universe. Just like how bricks come together to build a house, atoms combine in different ways to create all the materials we see in the world. Atoms are so small that a single speck of dust contains more atoms than all the people on Earth!
Atom Fact!
There are about 7 billion billion billion atoms in a human body! That's 7 followed by 27 zeros!
Atomic Structure
Atoms are made of three smaller particles:
Protons
Positively charged particles in the nucleus
Neutrons
Neutral particles in the nucleus
Electrons
Negatively charged particles orbiting the nucleus
The nucleus is at the center of the atom and contains protons and neutrons. This is where most of an atom's mass is located. The electrons orbit around the nucleus in different energy levels called shells.
Most of an atom is actually empty space! If an atom were the size of a football stadium, the nucleus would be like a marble at the center, and the electrons would be like tiny specks flying around in the stands.
Charge Balance
Atoms have equal numbers of protons and electrons, making them electrically neutral overall!
Atomic Number & Mass
The atomic number tells us the number of protons in an atom's nucleus. This number determines what element the atom is. For example:
• Hydrogen has atomic number 1 (1 proton)
• Carbon has atomic number 6 (6 protons)
• Oxygen has atomic number 8 (8 protons)
The atomic mass (also called mass number) is the total number of protons and neutrons in the nucleus. Since electrons are so light, they don't add much to the atom's mass.
Element Identity
Changing the number of protons creates a different element. Add one proton to hydrogen and you get helium!
Molecules & Compounds
Atoms rarely exist alone—they usually join together to form molecules and compounds:
• Molecules are groups of two or more atoms held together by chemical bonds
• Compounds are molecules made of different types of atoms
For example, a water molecule (H₂O) is a compound made of two hydrogen atoms and one oxygen atom. When atoms bond together, they create substances with completely new properties!
Water (H₂O)
Two hydrogen atoms + one oxygen atom
Oxygen (O₂)
Two oxygen atoms bonded together
Carbon Dioxide (CO₂)
One carbon atom + two oxygen atoms
Atoms Quiz
Test your atomic knowledge with this quiz! Answer all 5 questions to see how much you've learned.
Frequently Asked Questions
Here are answers to some common questions about atoms:
Amazing Atom Trivia
Discover some fascinating facts about atoms:
Ancient Idea
The concept of atoms was first proposed by ancient Greek philosophers around 400 BC. The word "atom" comes from the Greek word "atomos" meaning "indivisible."
Mostly Empty Space
Atoms are over 99.999% empty space! If you removed all the empty space from the atoms in every person on Earth, the entire human population would fit inside a sugar cube.
You're Made of Stardust
Nearly all the atoms in your body were created inside stars billions of years ago! When stars explode, they spread these atoms throughout space, which eventually formed our planet and everything on it.
Long-Lived Atoms
Atoms are incredibly durable. The atoms in your body are billions of years old and will continue to exist long after your lifetime, becoming part of other things in nature.
