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What is An Atom? - Definition & Examples

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  • 0:01 What Is an Atom?
  • 0:48 Protons, Neutrons & Electrons
  • 2:45 Elementary Particles
  • 3:45 Lesson Summary
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Lesson Transcript
Instructor: David Wood

David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

After watching this video, you will be able to explain what an atom is, how it is structured, what they are made from, and give some examples of elements. A short quiz will follow.

What Is an Atom?

An atom is the basic unit of a chemical element. Everything in the world is made out of atoms. Your computer monitor is made out of atoms. The desk it sits on is made out of atoms. So is the air you're breathing. In fact, you are also made out of atoms.

If you could somehow take yourself apart and break your body down to its most basic level, you would find that you're made out of living cells. And those cells are made out of complex molecules. And those molecules contain atoms bonded together.

Okay, but what is an atom? What does it look like? The most basic way we imagine atoms is just a series of circles or balls in a clump. But we need to talk about what's inside the circles, what makes them up, to really understand what an atom is.

Protons, Neutrons & Electrons

Atoms are made out of three main parts: protons, neutrons and electrons. Protons and neutrons are contained inside the very center of the atom, which is called the nucleus. Electrons orbit around the outside of the nucleus, similar to how the Earth orbits the sun. Most of the atom is empty space - both the nucleus and the electrons are so tiny that even solid objects are mostly empty. The desk in front of you, and in fact everything around you, is mostly empty space on an atomic level. But it still feels pretty solid to me!

Okay, so atoms are made out of protons, neutrons and electrons. But what are they? Protons are stable subatomic particles, with a positive +1 charge and a mass of approximately one atomic mass unit. Neutrons are stable subatomic particles with a neutral, or zero, charge and a mass of approximately one atomic mass unit. Neutrons have the same mass as protons but a neutral charge. That's why they're called neutrons... 'neutr' for 'neutral.' Last of all, electrons are stable subatomic particles, with a negative -1 charge and a mass 1/1836th of the mass of a proton. So, electrons are much smaller than protons or neutrons, but they contain a negative charge of the same size as much larger protons.

There are lots of types of atoms and those types are called elements. The element helium, for example, contains atoms with two protons in the nucleus. The element iron contains atoms with 26 protons. The element oxygen contains atoms with eight protons. And the element gold contains atoms with 79 protons.

When it comes to understanding atoms and the way they look and act, we only really need to know about protons, neutrons and electrons. But that's not really the end of the story.

Elementary Particles

An elementary particle is a particle that is the smallest and most basic component of matter and cannot be broken down into smaller particles. For example, the atom isn't an elementary particle because it contains protons, neutrons and electrons. But are they elementary particles?

It turns out that the tiny electrons are fundamental elementary particles - they are not made of particles any smaller. But protons and neutrons are not elementary particles. Protons and neutrons contain even smaller particles, called quarks. There are six types of quarks: up, down, strange, charm, top and bottom. Protons contain two up quarks and one down quark, and neutrons contain two down quarks and one up quark.

Maybe one day we'll discover that electrons and quarks are made of even smaller particles. But, at least for now, as far as we know, this is the smallest anything in the universe can get.

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