Matter is anything and everything in our surrounding. It has basic structural and fundamental units. Let us examine the concept of matter with an example. Taking a story book into consideration and dividing its structure. The book contains many pages, each page consists of paragraphs, and each paragraph has many sentences. Each sentence will further have many words and each word will have characters. Therefore we have divided a storybook into characters. This is exactly the same case when we take matter into account. Matter is made up of substances which contains molecules. The molecules in turn are made up of groups of atoms.
Atoms in simple terms are defined as the smallest unit of matter. In ancient times the scientists wondered whether matter could be further divided or not. Around 500 BC the idea of divisibility of matter evolved in India. A scientist named Maharishi Kanad stated that matter can be divided into smaller and smaller units. The smallest unit of matter after which further division was not possible was known as parmanu.
Properties of atoms and molecules
A molecule is defined as the smallest unit of a compound that contains the chemical properties of the compound. Molecules are made up of groups of atoms. Describing the structure of an atom, an atom is also sub-divided into smaller units. Proton, electrons and neutrons are sub-particles of an atom. The protons and neutrons are contained inside the nucleus of atom and electrons revolve around the nucleus. Protons are positively charged particles whereas electrons are negatively charged particles. Neutrons do not carry any charge. So we can say that the nucleus is positively charged due to the presence of protons. The nucleus is a bulk mass at the centre of an atom. Atoms are largely vacant.
Every element has certain atomic number. The atomic number of an element is defined as the number of protons present in its nucleus. It is denoted by Z.
When we talk about the mass of atoms, the mass of its particles is taken into consideration. Electrons have negligible mass. Hence the mass of an atom is the sum of the mass of protons and neutrons. The mass number is denoted by A.
We have briefly seen the properties of atoms and molecules. For NCERT Solutions for Atoms click on this link, NCERT Solutions for Atoms