Question

Define elements, compounds and molecules.

Answer 1

Hint: Element is a pure form of substance which consists of atoms only. Compounds consist of elements in the fixed proportion. Molecules are made up of two or more than two atoms. These atoms may be the same or different.

Complete answer:
In chemistry if we talk about the elements we can say that they are the purest form of chemical substances which cannot be further broken down into constituents by ordinary chemical and physical methods consisting of atoms . Some examples of elements are Gold, silver, hydrogen, oxygen etc.
Elements can be further classified into following categories:
(a)Metals: Metals are those elements which possess a characteristic lustre, malleability, ductility and are good conductors of heat and electricity. For example: Silver, gold etc.
(b) Non-metals: Non – metals are those elements which do not possess shine and are generally brittle and also poor conductors of electricity. For example: Carbon, phosphorus etc.
(c) Metalloids: The elements which possess properties of both metals and non- metals are called metalloids. For example: Germanium, arsenic etc.
Compounds: They are also regarded as pure substances. Compounds are made up of two or more elements in a definite ratio by mass. They can be decomposed by chemical means into chemical constituents.
For example: Water is a compound because it is made up of two or more elements hydrogen and oxygen in the ratio 1: 8 by mass. It can be decomposed into its constituent elements $H$ and $O$ by passing electric current into it. Similarly sodium chloride is a compound because it is made up of two elements that are sodium and chlorine and it can be further decomposed into its constituent elements sodium and chlorine by passing electric current.
The properties of compounds are different from those of constituent elements because if we take sodium chloride then sodium chloride does not get burned in water but sodium when placed in contact with water it starts burning.
(c) Molecules: Molecules are the smallest particles of substance (element or compound) which can exist independently. Molecules are made up of two or more atoms of the same or different type. Depending on the type of elements present in them they are classified as:
Homoatomic molecules: When a molecule is composed of the same atoms then it is called a monatomic molecule. For example: ${H_2},{N_2}$ .
Heteroatomic molecules: When a molecule is composed of two or more different atoms then it is called a heteroatomic molecule. For example: $HCl,{H_2}S$ .

Note:Generally many elements are present in nature in compound form. Elements cannot be broken down further into smaller substances. All molecules are compounds but all compounds are not molecules. Because a molecule can be made of two same atoms but compounds are made up of two or more different types of atoms.