⬆️ TOP EDUCATION ⬆️
CLASS 9 SCIENCE
CHAPTER 4 STRUCTURE OF THE ATOM
NOTES
1. Atom: An atom is the smallest unit of matter that retains the properties of an element. It consists of three main subatomic particles:
👉Protons: Positively charged particles present in the nucleus.
👉Neutrons: Neutral particles present in the nucleus.
👉Electrons: Negatively charged particles that revolve around the nucleus in specific energy levels or shells.
2. Atomic Number: The atomic number of an element is the number of protons present in the nucleus of an atom of that element. It is denoted by the symbol 'Z.' The atomic number determines the identity of an element.
3. Mass Number: The mass number of an atom is the sum of the number of protons and neutrons present in the nucleus. It is denoted by the symbol 'A.'
4. Isotopes: Isotopes are atoms of the same element having the same atomic number but different mass numbers. They have the same number of protons but different numbers of neutrons.
5. Valency: The valency of an element is the combining capacity of its atom. It is determined by the number of valence electrons (electrons in the outermost shell) an atom possesses. The valency determines the way an element can combine with other elements to form compounds.
6. Electronic Configuration: The electronic configuration of an atom describes the arrangement of electrons in different energy levels or shells. The distribution of electrons follows the Aufbau principle, Pauli's exclusion principle, and Hund's rule.
7. Bohr's Model of an Atom: According to the Bohr model, electrons revolve around the nucleus in specific circular orbits or energy levels. Each energy level has a fixed energy associated with it. Electrons can move between energy levels by gaining or losing energy.
8. Rutherford's Gold Foil Experiment: Rutherford's experiment demonstrated that the atom has a small, dense, and positively charged nucleus, with electrons revolving around it. Most of the space inside an atom is empty.
9. Neils Bohr's Model of an Atom: Bohr proposed that electrons occupy specific energy levels or shells and revolve in fixed orbits without emitting radiation. Electrons can jump from one energy level to another by absorbing or emitting energy in discrete quantities.
10. Modern Atomic Model: The modern atomic model incorporates the wave-particle duality of electrons and describes the electron's probable location in an atom using orbitals. Orbitals are regions of space where electrons are likely to be found.
☆These are some key points from Chapter 4 of Class 9 Science. It's advisable to refer to your textbook for a more comprehensive understanding of the topic.