Ionic Bonding and Ion Formation

Ionic Bonding

Atoms that have gained or lost electrons bond to form ionic compounds.

Ions

  • Atoms can have an overall neutral charge.
  • Protons have a positive charge, and electrons have a negative charge.
  • In a neutral atom, the positive charge of protons equals the negative charge of electrons.
  • The atomic number indicates the number of protons or electrons in an element.
  • The mass number minus the atomic number equals the number of neutrons.
  • Example: Lithium has 3 protons (+3) and 3 electrons (-3), resulting in a neutral charge.

Cations

  • If an atom loses an electron, it results in an overall positive charge.
  • This is because there is now an extra proton compared to the number of electrons.
  • This positively charged ion is called a CATION.

Anions

  • If an atom gains an electron, it results in an overall negative charge.
  • This is because there is now an extra electron compared to the number of protons.
  • This negatively charged ion is called an ANION.
  • Anion = negative.

Why Atoms Lose or Gain Electrons

  • Atoms lose or gain electrons to achieve a stable electron configuration in their outermost shell.
  • Electron shells are most STABLE when they are FULL or contain the maximum number of electrons possible.
  • Electron shell maximums:
    • First shell: 2 electrons
    • Second shell: 8 electrons
    • Third shell: 8 electrons (or 18, but we consider it 8)
  • Helium has 2 electrons (electron configuration: 2) and a full first electron shell, making it stable.
  • Neon has 10 electrons (electron configuration: 2,8) and full first and second electron shells, making it stable.

Ions Recap

  • A charged atom is called an ion.
  • The process of forming an ion is called ionization.
  • Atoms that lose or gain electrons become charged – either positively (cation) or negatively (anion).
  • Electron shells are most STABLE when they are FULL or contain the maximum number of electrons possible.
  • Atoms will gain or lose electrons in the outer electron shell to try to get a FULL outer electron shell.

Ionization Example 1: Chlorine

  • Chlorine atom has an electronic configuration of 2,8,7.
  • It gains an electron to form the chloride ion with an electronic configuration of 2,8,8 – a full outer shell.
  • The number of protons in the chloride ion remains 17 (number of protons doesn’t change during ionization).
  • The charge of the chloride ion is -1 because it now has 18 electrons (-18) but only 17 protons (+17).

Ionization Example 2: Magnesium

  • Magnesium atom has an electronic configuration of 2,8,2.
  • It has two electrons in its outer shell and tends to lose them to achieve a full outer shell.
  • It's easier to get rid of 2 electrons than to gain 6.
  • The new electronic configuration of the magnesium ion is 2,8.
  • The number of protons in the magnesium ion remains 12.
  • The charge of the magnesium ion is +2 (or Mg^{2+}) because it has lost two electrons.

Ions Recap

  • A charged atom is called an ion.
  • The process of forming an ion is called ionization.
  • Atoms that lose or gain electrons become charged – either positively (cation) or negatively (anion).
  • When ions are formed, the charge on the ion is determined by the number of electrons gained or donated.
  • If electrons are donated, then the charge on the ion is positive because the ion has more protons (+) than electrons (-).
  • If electrons are gained, then the charge of the ion is negative because the ion has more electrons (-) than protons (+).

Task: Completing Ionic Charge Table

  1. Download the ionic charge table.
  2. Complete the table with the elements provided, using the periodic table to help determine electronic configurations and charges.

Elements:

  • Hydrogen (H)
  • Lithium (Li)
  • Beryllium
  • Boron
  • Carbon
  • Nitrogen
  • Oxygen
  • Fluorine
  • Sodium
  • Magnesium
  • Aluminium
  • Silicon
  • Phosphorus
  • Sulphur
  • Chlorine
  • Potassium
  • Calcium

Periodic Table

The periodic table organizes elements by atomic number, chemical symbol, atomic mass, and name. It distinguishes between metals, non-metals, transition metals, and rare earth elements.

Challenge Question

Neon (atomic number 10) and argon (atomic number 18) do not normally form ions because they have full outer electron shells and are stable.

Ionic Bonding

  • Positively charged cations are attracted to negatively charged anions.
  • Cations and anions with opposite charges combine to form an ionic bond; the positive charge is balanced by an equal negative charge.
  • A cation with a 2+ charge is likely to bond with an anion with a 2- charge or with two anions with a charge of 1-.
  • Example: Na^+ and Cl^- bond to form the ionic compound NaCl (table salt).

Reflection

  • Ions are formed when atoms gain or lose electrons.
  • A cation is a positively charged ion.
  • An anion is a negatively charged ion.
  • An ionic bond is the attraction between oppositely charged ions.