A pair of electrons, shared by two positively charged nuclei and attracted by both nuclei at the same time is called chemical bonding. Chemical bonds occur when elements react and form a compound.
Note that the metallic and non metallic behaviours of elements in the periodic table vary vertically and horizontally.
(I) Metallic character: elements that easily lose electrons exhibit metallic behaviour. Elements on the left hand side of the periodic table lose electrons more easily than the elements on the right hand side.
(II) Non metallic character: it consists of atoms that hold tightly to their valence electrons. So moving from from left to right across a period, non metallic properties begin to appear half way across and increase from left to right. But within the group, the non metallic characters of the elements decrease as you move from top to bottom.
Atomic properties and periodicity
1.Ionization energy: this is the energy required to remove a valence electron from an atom of the element to form an ion. Thus moving from left to right across a period, there is a general rise in the first ionization energy. This is as a result that the nuclear charge is increasing across the period.
2. Electron affinity: it is the energy change that occurs when an isolated gaseous atom acquires an electron and so becomes a negative charge ion.e.g X + e– > X– .
Diagram of atomic radius
3. Atomic radii: it is defined as half the distance between the nuclei when the bond linking the atoms is a single covalent bond. Or it can also be defined as the distance of closest approach to another atom in a given bonding situation.
When moving down a group of the periodic table, the atomic radii increases, although the nuclear charge increases considerably, the extra electrons are entering new shells further from the nucleus.
Diagram of electron affinities in KJ mol-1
Ionic radii: it deals with electrovalent compounds and it varies periodically like the atomic radii i.e it decreases across the period and increases down the group.
Diagram plot of atomic radius against atomic number
Determination of ionic radii
A study of the variation of ionic radii with atomic numbers shows that:
(I) cations have smaller ionic radii than the corresponding atomic radii since their nuclear charge and consequently the electrons are attracted more strongly. (Positive ion is always smaller than the neutral atom from which it is derived)
(II) Anions have larger ionic radii than the corresponding atomic radii because the protons are exceeded by the electrons and the electrons repel one another. (Negative ion is always larger than its parent atom)
4. Electronegativity: it is a measure of the ability of an atom in a molecule to attract electrons to itself. Electronegativity of elements increases across a period but decreases down a group.
Diagram of periodicity of electronegativity with atomic number for the first twenty elements
Note that electronegativity can be used to predict the type of bonding a compound will have.
Average bond energies of some bonds
|Bond||Bond energy (KJ mol-1)||Bond||Bond energy (KJ mol-1)|
|H – HO = OCl – ClC – CC – HC – ClO – H||435498243347414338464||N – NN – HH – ClC – OC = OC = CC = C||941389431360736611837|
Note: lattice energy of an ionic crystal is the heat of formation of one mole of ionic compound from widely separated gaseous ions under standard conditions.
It is the process whereby orbitals of different shape and geometry combine or mixed together to produce an orbital of suitable geometry which can overlap maximally during bond formation. Examples of hybrid orbitals are sp, sp2, sp3, sp2d and sp3d and sp3d2 hybrid orbitals.
Diagram of orbital hybridization
Diagram of bond distance and bond angles in a molecule
Diagram of linear shape in hydrogen, oxygen and chlorine
Diagram of linear shape in carbon (IV) oxide
Types of crystalline solids
- Covalent solids
- Ionic solids
- Metallic solids
- Molecular crystal
1.the bond formed between two elements with electron configuration 1s22s22p63s2 and 1s22s22p4 is? (Jamb 2013)
Solution: (1s22s22p63s2 total electrons are 12. It has two electrons at the outermost shell i.e. it can give out 2 electrons)
(1s22s22p4 total electrons are 8. It has four electrons at the outermost shell)
(Mg – 2e-) + (O + 2e-) > Mg2+ + O2-
Mg + O > Mg2+O2-
2. If the difference in electronegativity of elements P and Q is 3.0. The bond that will be formed between them is? (Jamb 2014)
3. Hydrogen bond can be found in? ( Jamb 2018)
A. Hydrogen sulphide
B. Hydrogen bromide
C. Hydrogen fluoride
D. Hydrogen chloride
4. The bond that is likely to be formed between elements X with electron configuration 2,8,2 and Y with electron configuration 2,8,7 is? (Jamb 2017)
5. Defined chemical bond?
Answer: a pair of electrons, shared by two positively charged nuclei and attracted by both nuclei at the same time is chemical bond
6. Define the following terms: (I) bond energy (ii) electronegativity
Answer: the average amount of energy associated with making or breaking one mole of a particular bond in its gaseous state is its bond energy while electronegativity is a measure of the ability of an atom in a molecule to attract electrons to itself.