Atoms and Atomic Theory - Study Guide

Facts, Problems, and Quiz

Atom, Illustration

Atom Overview

Chemistry is the study of matter and the interactions between different types of matter and energy. The fundamental building block of matter is the atom. An atom consists of three main parts: protons, neutrons, and electrons. Protons have a positive electrical charge. Neutrons have no electrical charge. Electrons have a negative electrical charge. Protons and neutrons are found together in what is called the nucleus of the atom. Electrons circle around the nucleus.

Chemical reactions involve interactions between the electrons of one atom and the electrons of another atom. Atoms which have different amounts of electrons and protons have a positive or negative electrical charge and are called ions. When atoms bond together, they can make larger building blocks of matter called molecules.

Important Atom Facts

All matter consists of particles called atoms. Here are some useful facts about 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.

Study Questions and Answers

Try these practice problems to test your understanding of atomic theory.

  1. Write the nuclear symbols for three isotopes of oxygen in which there are 8, 9, and 10 neutrons, respectively. Answer
  2. Write the nuclear symbol for an atom with 32 protons and 38 neutrons. Answer
  3. Identify the number of protons and electrons in the Sc3+ ion. Answer
  4. Give the symbol of an ion which has 10 e- and 7 p+. Answer