SPM Chemistry Form 4 Notes – Chemical Bonds (Part 2)

by BerryBerryTeacher

in Berry Reference (Notes)

Ionic Bond is one of the two main chemical bonds that Berry Readers will learn as a chemistry SPM student. Ionic bond is simply a bond formed when there are electrostatic attraction between two oppositely charged ions. Typically, ionic bonds are formed between a metal (cation) and non-metal (anion). Bonds with greater difference in the electronegativity between the involved atoms will be more ionic.

If it is starting to sound confusing for you, fret not! That was just a teaser from Berry Berry Easy on ionic bonds, and this post is the Part 2 of SPM Chemistry Form 4 notes on Chemical Bonds. In this part, you’ll learn about the basics of ionic bonds (definition), metals and non-metals (and how they form ionic bonds), structure of ionic compound and predicting the formula of an ionic compound.

[Tips: Learn to at least recognise that ionic bonds must consist of a metal and non-metal. Try and memorise common pairs of ionic compounds after you understand how they are formed. Draw many many many diagrams of ionic compounds. With these, you should easily master the basics of ionic bonds.]

SPM Chemistry Form 4 Notes – Chemical Bonds (Part 2)

Ionic lattice structure

Ionic lattice structure

Ionic Bonds

  • It is a chemical bond formed from the transfer of electrons from metal atoms to non-metal atoms
  • Metal atoms donate valence electrons to form positive ions (cations, Mb+) and achieve the stable duplet or octet electron arrangement of the noble gases
  • Non-metal atoms receive electrons to form negative ions (anions, Xa-) and achieve the stable duplet or octet electron arrangement of the noble gases
  • Cations and anions are attracted to each other by strong electrostatic force of attraction

Example:

Metal + Non-metal –> Ionic compound
Sodium + bromine –> Sodium bromide
Calcium + chlorine –> Calcium chloride
Lithium + oxygen –> Lithium oxide
Aluminium + nitrogen –> Aluminium nitride

Metals

Group 1

  • A lithium atom with an electron arrangement of 2.1 achieves stability after it donates one valence electron to form a lithium ion, Li+. The electron arrangement of the lithium ion, Li+, is 2 with stable duplet electron arrangement.
  • A sodium atom with an electron arrangement of 2.8.1 achieves stability after it donates one valence electron to form a sodium ion, Na+. The electron arrangement of the sodium ion, Na+, is 2.8 with stable octet electron arrangement.
  • A potassium atom with an electron arrangement of 2.8.8.1 achieves stability after it donates one valence electron to form a potassium ion, K+. The electron arrangement of the potassium ion, K+, is 2.8.8 with stable octet electron arrangement.

Group 2

  • A magnesium atom with an electron arrangement of 2.8.2 achieves stability after it donates two valence electrons to form a magnesium ion, Mg2+. The electron arrangement of the magnesium ion, Mg2+, is 2.8 with stable octet electron arrangement.
  • A calcium atom with an electron arrangement of 2.8.8.2 achieves stability after it donates two valence electrons to form a calcium ion, Ca2+. The electron arrangement of the calcium ion, Ca2+, is 2.8.8 with stable octet electron arrangement.

Group 13

  • An aluminium atom with an electron arrangement of 2.8.8.3 achieves stability after it donates three valence electrons to form an alumium ion, Al3+. The electron arrangement of the aluminium ion, Al3+, is 2.8.8 with stable octet electron arrangement.

Non-metal

Group 15

  • A nitrogen atom with an electron arrangement of 2.5 achieves stability after it accepts three valence electrons to form a nitride ion, N3-. The electron arrangement of the nitride ion, N3-, is 2.8 with stable octet electron arrangement.
  • A phosphorus atom with an electron arrangement of 2.8.5 achieves stability after it accepts three valence electrons to form a phosphoride ion, P3-. The electron arrangement of the phosphoride ion, P3-, is 2.8.8 with stable octet electron arrangement.

Group 16

  • An oxygen atom with an electron arrangement of 2.6 achieves stability after it accepts two valence electrons to form a oxide ion, O2-. The electron arrangement of the oxide ion, O2-, is 2.8 with stable octet electron arrangement.
  • A sulphur atom with an electron arrangement of 2.8.6 achieves stability after it accepts two valence electrons to form a sulphide ion, S2-. The electron arrangement of the sulphide ion, S2-, is 2.8.8 with stable octet electron arrangement.

Group 17

  • A fluorine atom with an electron arrangement of 2.7 achieves stability after it accepts one valence electron to form a fluoride ion, F -. The electron arrangement of the fluoride ion, F -, is 2.8 with stable octet electron arrangement.
  • A chlorine atom with an electron arrangement of 2.8.7 achieves stability after it accepts one valence electron to form a chloride ion, Cl -. The electron arrangement of the chloride ion, Cl -, is 2.8.8 with stable octet electron arrangement.

Predict the Formula of an Ionic Compound

  • Cation Mb+
  • Anion Xa-
  • Formula of an ionic compound formed, MaXb

Formulae for ionic compound

Metal atom, M Non-metal atom, X Ionic Compound
Group 1 Group 15 M3X
Group 1 Group 16 M2X
Group 1 Group 17 MX
Group 2 Group 15 M3X2
Group 2 Group 16 MX
Group 2 Group 17 MX2
Group 13 Group 15 MX
Group 13 Group 16 M2X3
Group 13 Group 17 MX3

Some common ionic compound

  • Sodium chloride (NaCl)
  • Magnesium oxide (MgO)
  • Calcium sulphide (CaS)
  • Potassium oxide (K2O)
  • Magnesium fluoride (MgF2)

Structure of ionic compounds

  • The oppositely-charged ions, Mb+ and Xa- are attracted to each other by a strong electrostatic force.
  • It form a rigid 3-dimensional lattice structure
  • Formed crystal.
  • Giant ionic lattice.

Berry Important Notes:

In the diagram of ionic compound, always shows

  • The outermost shells of all ions must achieve a stable duplet or octet electron arrangement.
  • The charge of each ion must be placed outside the bracket.
  • Label the ions.

In the next part (Part 3) of Berry Berry Easy notes on Chemical Bonds for SPM Form 4 chemistry students, Berry Readers will learn covalent bonds and the non-metals needed to form the bonds, the different types of covalent bonds, examples and structure of covalent compounds.

[Extra: Pure ionic bonds cannot actually be formed as all ionic compounds have some levels of covalent bonding. However, this is not covered in the syllabus, hence it'll only be for your own reference, in case you do extra reading online and get confused. Hence, the traditional ionic bond only exist when ionic character > covalent character]

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