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Basic Model of the Atom

Introduction to Atoms


This is a diagram of a helium atom, which has 2 protons, 2 neutrons, and 2 electrons.

This is a diagram of a helium atom, which has 2 protons, 2 neutrons, and 2 electrons.

Svdmolen/Jeanot, Public Domain

All matter consists of particles called atoms. This is a list of the basic characteristics of atoms:

  • Atoms cannot be divided using chemicals. They do consist of parts, which include protons, neutrons, and electrons, but an atom is a basic chemical building block of matter.


  • Each electron has a negative electrical charge.


  • Each proton has a positive electrical charge. The charge of a proton and an electron are equal in magnitude, yet opposite in sign. Electrons and protons are electrically attracted to each other.


  • Each neutron is electrically neutral. In other words, neutrons do not have a charge and are not electrically attracted to either electrons or protons.


  • Protons and neutrons are about the same size as each other and are much larger than electrons. The mass of a proton is essentially the same as that of a neutron. The mass of a proton is 1840 times greater than the mass of an electron.


  • The nucleus of an atom contains protons and neutrons. The nucleus carries a positive electrical charge.


  • Electrons move around outside the nucleus.


  • Almost all of the mass of an atom is in its nucleus; almost all of the volume of an atom is occupied by electrons.


  • The number of protons (also known as its atomic number) determines the element. Varying the number of neutrons results in isotopes. Varying the number of electrons results in ions. Isotopes and ions of an atom with a constant number of protons are all variations of a single element.


  • The particles within an atom are bound together by powerful forces. In general, electrons are easier to add or remove from an atom than a proton or neutron. Chemical reactions largely involve atoms or groups of atoms and the interactions between their electrons.

Does the atomic theory make sense to you? If so, here's a quiz you can take to test your understanding of the concepts.

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