2.2 Ions & Ionic Bonds

• An ion is an electrically charged atom or group of atoms formed by the loss or gain of electrons
• An atom will lose or gain electrons to become more stable
• The loss or gain of electrons takes place to gain a full outer shell of electrons which is a more stable arrangement of electrons
• The electronic configuration of an ion will be the same as that of a noble gas – such as helium, neon and argon
• Formation of positively charged sodium ion
• Formation of negatively charged chloride ion
• Metals can lose electrons to other atoms to become positively charged ions, known as cations
• Non-metals can gain electrons from other atoms to become negatively charged ions, known as anions
• Ionic compounds are formed when metal atoms react with non-metal atoms
• Metal atoms lose their outer electrons which the non-metal atoms gain to form positive and negative ions
• The positive and negative ions are held together by strong electrostatic forces of attraction between opposite charges
• This force of attraction is known as an ionic bond and they hold ionic compounds together
• Dot-and-cross diagrams
• Dot and cross diagrams are diagrams that show the arrangement of the outer-shell electrons in an ionic or covalent compound or element
• The electrons are shown as dots and crosses
• In a dot and cross diagram:

  • Only the outer electrons are shown
  • The charge of the ion is spread evenly which is shown by using brackets
  • The charge on each ion is written at the top right-hand corner
  • Electrostatic forces between the positive Na ion and negative Cl ion
• Ionic bonds between Group I & Group VII Elements
• Example: Sodium Chloride, NaCl
• Sodium chloride ionic bonding explanation
• Sodium is a Group I metal so will lose one outer electron to another atom to gain a full outer shell of electrons

  • A positive sodium ion with the charge 1+ is formed
  • Chlorine is a Group VII non-metal so will need to gain an electron to have a full outer shell of electrons
  • One electron will be transferred from the outer shell of the sodium atom to the outer shell of the chlorine atom
  • A chlorine atom will gain an electron to form a negatively charged chloride ion with a charge of 1-
• The oppositely charged ions are held together by strong electrostatic forces of attraction
• The ionic compound has no overall charge
• Formula of ionic compound: NaCl
• Ionic compounds have a giant lattice structure
• Lattice structure refers to the arrangement of atoms of a substance in 3D space
• In lattice structures, atoms are arranged in an ordered and repeating fashion
• The lattices formed by ionic compounds consist of a regular arrangement of alternating positive and negative ions
• The lattice structure of NaCl consists of a regular arrangement of alternating positive and negative ions
• Ionic compounds are formed when metal atoms and non-metal atoms react
• Example: Magnesium Oxide, MgO
• Magnesium is a Group II metal and will lose two outer electrons to another atom to have a full outer shell of electrons
• A positive ion with the charge 2+ is formed
• Oxygen is a Group VI non-metal and will need to gain two electrons to have a full outer shell of electrons
• Two electrons will be transferred from the outer shell of the magnesium atom to the outer shell of the oxygen atom
• Oxygen atom will gain two electrons to form a negative ion with charge 2-
• Magnesium oxide has no overall charge
• Properties of Ionic Compounds
• Ionic compounds are usually solid at room temperature
• They have high melting and boiling points
• Ionic compounds are good conductors of electricity in the molten state or in solution