Atomic Number and Mass Number

• What is the atomic number of an element?

  It is the number of protons in atoms of that element.
• What does the mass number represent?

  It is the total number of protons and neutrons in an atom.
• Why do atoms have no overall charge?

  Because the number of electrons equals the number of protons.
• How can you determine the number of neutrons in an atom?

  • Subtract the atomic number from the mass number.
• How many protons and electrons does a lithium atom have?

  Three protons and three electrons.
• How many neutrons does a lithium atom contain?

  Four neutrons.
• What are isotopes?

  • Atoms of the same element
  • Different numbers of neutrons
• What is a key fact about the number of protons in atoms of the same element?

  All atoms of the same element have the same number of protons.
• How many protons and neutrons does the first isotope of chlorine contain?

  Seventeen protons and eighteen neutrons.
• How many protons and neutrons does the second isotope of chlorine contain?

  Seventeen protons and twenty neutrons.
• What defines an ion?

  • Atoms with an overall charge
  • Caused by losing or gaining electrons
• What happens to a sodium atom to become a positive ion?

  It loses one electron.
• What happens to a fluoride atom to become a negative ion?

  It gains one electron.
• How many protons, neutrons, and electrons does an oxide ion have?

  Eight protons, eight neutrons, and ten electrons.
• How many protons, neutrons, and electrons does an aluminium ion have?

  Thirteen protons, fourteen neutrons, and ten electrons.