STRUCTURE AND BONDING
Introduction
During a chemical reaction, atoms of the same or different elements combine by a mutual force of attraction developing between them. Atoms of other elements achieve the stable electron arrangement of noble gases by gaining, losing or sharing the valence electrons.
A chemical bond
It is the mutual force of attraction which holds the atoms of the same or different elements together.
A structure
It is a regular pattern in which chemical bonds hold the particles of a substance together.
Types of chemical bonds
1. Ionic Bond (electrovalent bond)
An ionic bond is the electrostatic force of attraction between ions with opposite charges. Â An ionic bond is formed when there is a complete transfer of valence electrons from one atom to another, resulting in two ions with opposite charges, which mutually attract one another. The resulting compound is known as an ionic compound.
Generally, the reaction between metals and non-metals results in the formation of ionic compounds. For example, sodium reacts with chlorine to form sodium chloride. The sodium atom reacts by losing its single valence electron to the chlorine atom. The resulting sodium particle has 10 electrons and 11 protons. This results in the formation of a sodium ion with a net positive charge, Na+. The chlorine atom on the other hand, accepts the electron donated by the sodium atom into its outermost energy level. The resulting particle (a chloride ion) has 18 electrons and 17 protons. Thus the chloride ion formed has net negative charge, Cl–.
The sodium ion with a net positive charge and the chloride ion with a net negative charge attract each other using ionic bond. These results in the formation of a compound referred to as an ionic compound. Other examples of ionic compounds include; potassium fluoride, magnesium oxide and magnesium chloride.
 Giant Ionic Structures
They are crystals (crystalline solids) with many ions joined by ionic bonds. A crystal is a solid form of a substance, in which the particles are arranged in a definite pattern repeated regularly in three dimensions. Most ionic substances are crystalline in nature.
2. Covalent and Co-ordinate Bond
Covalent bond
   A covalent bond is a bond formed when the combining atoms share a pair (or pairs) of electrons between them, each donating an electron to the shared pair. Covalent bonding occurs when atoms of non-metals combine. The combining atoms could be of the same element or from different elements. It is common in molecules. Substances with covalent bonds either have molecular or giant atomic structures.
   A molecule is a group of atoms (two or more) of the same or different elements that are held together by strong covalent bonds. Substances consisting of molecules include; water, most gases, sugar, oils, fats, naphthalene, paraffin wax and sulphur. Substances consisting of molecules are referred to as molecular substances.
For example, two hydrogen atoms can combine to form a hydrogen molecule. Each hydrogen atom has only one electron in its occupied energy level. It therefore needs to gain one electron to attain the stable electron arrangement of helium (duplet state). Since the combing atoms are of the same element, none would readily lose an electron to the other. The atoms therefore end up sharing a pair of electrons, each atom contributing an electron to the shared pair.
Co-ordinate Bond (Dative bond)
A co-ordinate bond is a type of a covalent bond in which the shared pair of electrons forming the bond is contributed by only one of the atoms combining. Examples of substances which have coordinate bonds include; ammonium ion (NH4+) ,carbon (II) oxide (CO), hydroxonium ion (H3O+), Ozone (O3), aluminium chloride dimer (Al2Cl6 ) and nitric (v) acid (HNO3)
4.Van der Waals forces
They are weak forces of attraction between molecules or atoms which exist only when the particles are close together. In molecules such as iodine, the atoms forming the molecules are held together by strong covalent bonds. The molecules are in turn held together in a regular pattern by weak van der Waals forces. The regular pattern repeats itself many times resulting to a molecular structure.
Molecular Structures
Most molecular substances are gases or liquids at room temperature. Some molecular substances include sulphur, sugar, iodine, fats, paraffin wax and naphthalene.
Giant Covalent Structure (Giant Atomic structures)
   A giant covalent structure is a structure that consists of an indefinite number of atoms which are all covalently bonded together. The pattern repeats itself and extends in all directions. Substances with giant atomic structures include diamond, graphite and silicon (IV) oxide.
5.The Metallic Bond
   Metallic bond is the electrostatic force of attraction between the positive nuclei and the delocalised valence electrons in the metallic structure. In a metallic structure, there are many atoms surrounding any one atom. The valence electrons are therefore mutually attracted to many nuclei.
   This gives rise to a situation where the positive nuclei appear to be immersed in a sea of mobile electrons. The mobile electrons in the structure are said to be delocalised. Metallic bonds are strong bonds. The pattern is repeated many times resulting in a giant metallic structure.
Types of Bonds and structures across a Period
Bond types vary from metallic to covalent across a period. The structures also vary from giant metallic, giant covalent to molecular. It is expected that similar compounds of the elements in period 3 will exhibit variation in bond types, structure and properties.
 NOTE:
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Conclusion
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STRUCTURE AND BONDING