Molecules of Compounds: An Introduction
A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds. Molecules are the smallest particles of a substance that have all of the physical and chemical properties of that substance. Biological molecules such as protein and DNA are made up of many thousands of atoms. A compound is a molecule made of atoms from different chemical elements. Compounds can be classified into two types, i.e., molecular compounds and ionic compounds. They can be broken down chemically only. Compounds contain a fixed ratio of atoms, held together by chemical bonds. Compounds are homogeneous in nature and cannot be separated physically.
What are Molecules of Compounds?
A combination of two or more atoms of different types is called a molecule of the compound. This means molecules of compounds have atoms of two or more different chemical elements, for example, methane, water, carbon dioxide, ammonia etc. We can further classify them on the basis of the number of atoms present in the molecule. The chemical bonding between the atoms can be either a covalent bond or an ionic bond. Ionic bonds always form between a molecule which has cations (positive ions) and anions (negative ions). Therefore, ionic compound always forms between two different chemical elements. Covalent bonds are formed by equal sharing of electrons between two atoms.
What are the Types of Elements and Compounds?
Elements are divided into three types:
Non-metals and
Metals: Substances having characteristics properties like malleability, ductility, sonority, electrical and thermal conductivity, lustre and solidness are called metals. Metals have high melting points. Most pure metals come from the earth’s crust. They are found in ores, which is a solid material. For example, zinc, iron, copper, aluminium, lead, chromium, cadmium, nickel, tin, zinc etc.
Non-metals: Non-metals are substances that do not conduct heat and electricity and are neither malleable nor ductile. For example, carbon, sulphur, phosphorus, silicon, oxygen etc.
Metalloid: A metalloid is a type of chemical element which has properties of both metals and nonmetals. The properties of the metalloids lie in between the metals and non-metals. For example, arsenic, silicon, boron etc.
Compounds are classified into two types:
Molecular compounds
Ionic compound.
Molecular Compounds: Molecules can be defined as the compound which can be formed by the combination of the same atom or different atoms. The atoms are joined to give a definite shape which is defined by the angles between the bonds and by the bond lengths. For example, carbon dioxide, water, ammonia etc.
Ionic Compound: It is made up of positive ions and negative ions. They break completely into ions when dissolved in water. For example, sodium chloride (NaCl), potassium chloride (KCl), copper sulphate (CuSO4) etc.
Examples of Molecules of Compounds
Some examples of molecules of a compound are given below:
H2O, NH3, CH4, CO2 are molecules of compounds with covalent bonding.
Water Molecule
The above image shows the structure of molecules of water in which two hydrogen atoms are covalently bonded with oxygen atoms and two lone pairs are present on oxygen atoms. The geometry of the water molecule is tetrahedral and the shape is bent.
Ammonia Molecule
The above image shows the structure of molecules of ammonia in which three hydrogen atoms are covalently bonded with one nitrogen atom and one lone pair of electrons is present on the nitrogen atom. The geometry of the ammonia molecule is tetrahedral and the shape is pyramidal.
Methane Molecule
The above image shows the structure of molecules of methane in which four hydrogen atoms are attached to one carbon atom and form tetrahedral geometry.
Carbon Dioxide
The above image shows the structure of carbon dioxide in which two oxygens are bonded with one carbon atom by a double bond and form linear geometry.
Ionic Compounds
The above image shows the ionic interaction of potassium chloride.
Key Features
Molecules of compounds are the combination of two or more atoms of different types.
Metals can conduct electricity but non-metals cannot conduct electricity.
A metalloid has properties between metals and nonmetals.
The nature of compounds is homogenous.
FAQs on Molecules of Compounds
1. How molecules are formed?
When atoms approach one another closely, the electron clouds interact with each other and with nuclei. After the interaction, if the energy of the system becomes lower, then the atoms bond together to form a molecule.
2. What are the salts present in food? In what category, this salt can be classified as a molecular compound or ionic compound?
We use salts as an essential nutrient, providing flavour and texture. The salt is the main source of the diet which maintains the level of NaCl (Na) in our body. Salt is an example of an ionic compound and it has properties different from molecular compounds as it dissociates into ions when dissolved in water but molecular compounds generally do not dissociate into ions when dissolved in water.
3. What type of bond is characteristic of a molecular compound?
Molecular compounds form with covalent bonds, which share electrons, and the mutual attraction for the shared electrons holds the molecule together. Ionic compounds transfer electrons from one atom to another.
