3. structure 0f matter
- 2. Matter The things that occupy space and have a mass are called matter.
- 3. According to physical nature the matter can be classified in to three groups . – Solid – Liquid – Gas
- 4. According to chemical composition the matter can be classified in to two groups • Pure substances –Elements and Compounds • Mixtures –Homogeneous mixtures –Heterogeneous mixtures
- 5. Atoms • Atoms are the building units of matter. • The atom is composed of subatomic particles. • protons, electrons and neutrons are the main subatomic particles.
- 6. • The electron is a negatively charged particle. • Proton has a positive charge • While neutrons have no charge.
- 8. The nuclear model The Planetary Model of the Atom • Their Is a nucleus at the centre of the atom. • Protons and neutrons are accumulated in the nucleus • The nucleus is positively charged • Electrons revole around the nucleus • The number of electrons in an atom is equal to the number of protons. • the atom is electrically neutral. This atomic model was introduced by Ernest Rutherford in 1911
- 9. Bohr Model of the Atom • Niels Bohr further elaborated the Rutherford's model According to Bohr Model , • The electrons move in definite paths or shells around the positively charged nucleus.
- 10. Energy levels • There are four main energy levels or shells around the nucleus . • They are assigned either numbers 1, 2, 3, 4...... or letters K, L, M, N...... respectively starting from the nearest to the nucleus. • Each energy level has a specific energy • When moving away from the nucleus this energy increases. Nevertheless, the difference between the energy levels decreases
- 11. • In an atom, there is a maximum number of electrons in any energy level.
- 12. Atomic number The atomic number is the number of protons in an atom of the element. Atomic number = number of protons Atomic number symbol of the elemant
- 13. Mass number The sum of the number of protons and neutrons in the nucleus of an atom is called the mass number mass number = number of protons + number of neutrons symbol of the element mass number
- 15. Electronic Configuration The arrangement of electrons in the respective energy levels of an atom from the innermost level to the outer most level is known as its electronic configuration