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Atom Overview and Structure

Alexandrea Dillon, David Wood, Christianlly Cena
  • Author
    Alexandrea Dillon

    Alexandrea has taught secondary science for over six years. She has a bachelors degree in Teaching Secondary Science and a Masters of Education in Instructional Design. She's TESOL certified and a National Geographic Certified Educator. In addition, she was the spotlight educator for National Geographic in late 2019.

  • 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.

  • Expert Contributor
    Christianlly Cena

    Christianlly has taught college Physics, Natural science, Earth science, and facilitated laboratory courses. He has a master's degree in Physics and is currently pursuing his doctorate degree.

Learn about the parts of an atom and its overview and structure. Discover the neutrons, protons, and electrons that compose an atom, along with examples of atoms. Updated: 05/06/2022

The Atom

Atoms make up everything tangible in the known universe. Atoms make up people, the atmosphere, the Earth, and everything in it. The scientific definition of atom is the smallest unit of matter that can be divided without releasing electrically charged particles. Atoms are the basic building blocks of all matter. Once atoms are split apart, energy is released, but atoms themselves can be isolated without the generation of energy. What are atoms made of? They are comprised of three main parts:

  1. Protons
  2. Neutrons
  3. Electrons

These are defined at length later in this lesson. This artistic representation of a carbon atom shows protons, neutrons, and electrons as convention dictates. Usually, neutrons are blue, protons are red, and electrons are black. Molecules are combinations of atoms. For example, a sugar molecule contains 12 carbon atoms, 22 hydrogen atoms, and 11 oxygen atoms that are bonded together. Therefore, it has a chemical formula of C12H22O11.


This is an artistic rendering of a carbon atom, highlighting the three main components of atoms.

An artistic representation of a carbon atom. It has the chemical formula of C12H22O11.


While atoms are too small to be observed with the human eye, this is an incredible body of scientific evidence to support their existence. In 1808, chemist John Dalton developed the modern atomic theory. This knowledge was implemented by many other brilliant scientists, which led to the eventual development of a device called a mass spectrometer which can measure the masses of atoms, thereby identifying them, with incredible accuracy. Chemical reactions are predictable, with the same outcome every time the same reactants are combined.

What Is an Atom?

Look around you. Everything you see is made out of atoms.

Here are some examples:

  • The computer screen you're looking at
  • The chair you're sitting on
  • Even the air you're breathing into your lungs

These are all atoms. But what exactly is an atom? Atoms are the basic building blocks of everything in the world and, indeed, we often think of atoms as tiny little spheres. Like a bunch of marble piles on top of each other. But atoms aren't that simple; they're made of smaller parts called protons, neutrons, and electrons.

The protons and neutrons are found in the very center of the atom, which is called the nucleus. And the electrons orbit around the outside. We'll talk more about each of those parts later in this lesson.

Structure of the Atom
Structure of the Atom

But if you look at the model of the atom, what do you notice? Well, one thing you might notice is that those protons, neutrons, and electrons are all pretty small, at least if the diagram is drawn anything close to being to scale. In fact, atoms are mostly. . . nothing. They're mostly made of empty space.

So when you put your elbow down on your desk, why doesn't it go straight though? According to quantum mechanics, it's actually possible that it could go through. It's just very unlikely. Even though they're mostly empty space, there is a repulsive intermolecular force that you feel when you touch things. Note that intermolecular means between molecules. Those forces are strong enough that the desk still feels pretty solid.

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Structure of an Atom

The composition of each atom determines which material it makes up. For example, the metal nickel has 28 protons, 28 neutrons, and 28 electrons in each atom. The metal copper has 29 protons, 29 neutrons, and 29 electrons in each atom. The differences in components account for the differences in materials. For example, copper is a brown color and nickel is silver in color. Atoms are categorized in the periodic table by their atomic number, which is their number of protons. The number of neutrons contained in an atom can fluctuate for a variety of reasons and does not impact atomic number.

The different components of atoms also interact with each other energetically and have different amounts of mass. Atomic mass is the mass of each atom and is measured in atomic mass units (amu). The definition of atomic mass has evolved as the field of chemistry has evolved. Since the 1960s, one amu is considered equal to 1/12th of a carbon-12 atom. Previously, the standards had been in comparison to oxygen and hydrogen atoms. Each proton and neutron add 1 amu to the total weight of an atom.

The image of oxygen on the periodic table, seen here, shows both the atomic weight and the atomic number. Oxygen contains eight protons and is, therefore, number eight on the periodic table. Critically thinking readers may have noticed that the atomic weight of oxygen isn't listed as exactly 16. That's because the atomic mass listed on the periodic table is an average of all available isotopes of an atom. There is an uncommon isotope of oxygen that is slightly less than 16 amu.


Oxygen

The periodic table entry of oxygen, including its atomic mass and atomic number (8).


Neutrons

Take another look at the carbon atom featured earlier in this lesson. The round component made from red and blue balls is called the nucleus. The atomic nucleus is the center of the atom and is comprised of protons and neutrons. Neutrons are subatomic particles that give mass to atoms but do not have any charge. They are usually depicted in artistic renderings of atoms as either blue or grey due to their neutral charge. All atoms contain neutrons except for Hydrogen (H), which is comprised of a single proton and a single electron.

Protons

When discussing the question what are atoms made of?, perhaps the most important subatomic particle to consider is the proton. It is the number of protons that defines an atom's atomic number and many of its properties. Protons are also located in the nucleus, give mass to the atom, and have a positive charge.

Parts of an Atom

Like we said, atoms are made of three parts: protons, neutrons, and electrons. Those small parts are types of particles. And particles have properties, or features about them, that are important.

One of those properties is mass, or how much stuff they contain. Protons and neutrons have masses of 1 atomic mass unit (AMU). And electrons have a tiny, tiny mass of 1/1836th of the protons and neutrons.

Another important property is charge, or the amount of electrical energy. There are positive charges and negative charges; like charges repel and opposite charges attract. Protons have a +1 charge, electrons have a -1 charge, and neutrons are neutral. That's why we call them neutrons. So even though electrons are tiny in terms of mass, they have a charge that is just as big as a proton (but negative instead of positive).

Electrons are fundamental particles, because they can't be broken down any more. But protons and neutrons actually contain smaller particles inside them called quarks. You don't need to know much about them, unless you're a physics major in college. But just knowing they exist means you understand atoms better than most people.

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Video Transcript

What Is an Atom?

Look around you. Everything you see is made out of atoms.

Here are some examples:

  • The computer screen you're looking at
  • The chair you're sitting on
  • Even the air you're breathing into your lungs

These are all atoms. But what exactly is an atom? Atoms are the basic building blocks of everything in the world and, indeed, we often think of atoms as tiny little spheres. Like a bunch of marble piles on top of each other. But atoms aren't that simple; they're made of smaller parts called protons, neutrons, and electrons.

The protons and neutrons are found in the very center of the atom, which is called the nucleus. And the electrons orbit around the outside. We'll talk more about each of those parts later in this lesson.

Structure of the Atom
Structure of the Atom

But if you look at the model of the atom, what do you notice? Well, one thing you might notice is that those protons, neutrons, and electrons are all pretty small, at least if the diagram is drawn anything close to being to scale. In fact, atoms are mostly. . . nothing. They're mostly made of empty space.

So when you put your elbow down on your desk, why doesn't it go straight though? According to quantum mechanics, it's actually possible that it could go through. It's just very unlikely. Even though they're mostly empty space, there is a repulsive intermolecular force that you feel when you touch things. Note that intermolecular means between molecules. Those forces are strong enough that the desk still feels pretty solid.

Parts of an Atom

Like we said, atoms are made of three parts: protons, neutrons, and electrons. Those small parts are types of particles. And particles have properties, or features about them, that are important.

One of those properties is mass, or how much stuff they contain. Protons and neutrons have masses of 1 atomic mass unit (AMU). And electrons have a tiny, tiny mass of 1/1836th of the protons and neutrons.

Another important property is charge, or the amount of electrical energy. There are positive charges and negative charges; like charges repel and opposite charges attract. Protons have a +1 charge, electrons have a -1 charge, and neutrons are neutral. That's why we call them neutrons. So even though electrons are tiny in terms of mass, they have a charge that is just as big as a proton (but negative instead of positive).

Electrons are fundamental particles, because they can't be broken down any more. But protons and neutrons actually contain smaller particles inside them called quarks. You don't need to know much about them, unless you're a physics major in college. But just knowing they exist means you understand atoms better than most people.

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  • Activities
  • FAQs

Atom Crossword Puzzle

In this activity, you will check your knowledge regarding the definition, parts, and measurement of an atom as presented from the lesson.


Directions

Complete the crossword by filling in a word that fits each of the given clues. To do this, you can just right-click the crossword to save the image and print it. With a pencil and an eraser, neatly write your answers in the boxes provided.

Across

2. A large fraction of the atom's _____ is concentrated in its nucleus, which contains protons and neutrons.

5. Two electrons will tend to repel each other because both have a _____ electrical charge.

7. It is an uncharged elementary particle that forms part of the nucleus of an atom.

9. It is the subatomic particle having a negative charge and orbiting the nucleus.

10. _____ are particles believed to be the building blocks of protons and neutrons.

Down

1. Unlike protons, the electron is a fundamental particle that could never be _____ down.

3. A _____ is an analytical tool useful for measuring the mass of molecules present in a sample.

4. An electron microscope can be used to visualize objects in the size of an _____.

6. The massive, positively charged central part of an atom is known as the _____.

8. The absolute value of the _____ of an electron is equal to that of a proton.


Answer Key


What is an atom made of?

An atom is made of subatomic particles. The three subatomic particles are neutrons (neutral charge), protons (positive charge), and electrons (negative charge).

What is a simple definition of an atom?

Atoms are the building blocks of all matter in the universe. Atoms are the smallest unit of matter that can be divided without releasing electrically charged particles.

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