CBSE Class 9 Science Notes Chapter 4 Structure of the Atom
CBSE Class 9 Science Notes Chapter 4 Structure of the Atom
NOTES
• Dalton's Atomic Theory:
• All matter is made up of small particles called atoms.
• Atoms are indivisible and indestructible.
• All atoms of a given element are identical in mass and properties.
• Compounds are formed when atoms of different elements combine in fixed ratios.
• Discovery of Subatomic Particles:
• Electrons were discovered by J.J. Thomson using the cathode ray tube experiment.
• Protons were discovered by E. Goldstein using the anode ray experiment.
• Neutrons were discovered by J. Chadwick using the neutron scattering experiment.
• Properties of Subatomic Particles:
• Electrons are negatively charged and have a negligible mass.
• Protons are positively charged and have a mass of 1 atomic mass unit (amu).
• Neutrons have no charge and have a mass of 1 amu.
• Structure of an Atom:
• An atom consists of a positively charged nucleus at the center and negatively charged electrons revolving around the nucleus in circular orbits.
• The number of protons in the nucleus determines the atomic number of an element.
• The total number of protons and neutrons in the nucleus determines the mass number of an element.
• Isotopes are atoms of the same element with the same atomic number but different mass numbers.
• Atomic Models:
• Rutherford's nuclear model of the atom proposed that most of the mass of an atom is concentrated in its nucleus and electrons revolve around the nucleus in circular orbits.
• Bohr's model of the atom proposed that electrons revolve around the nucleus in fixed circular orbits at different energy levels.
• Valency:
• Valency is the combining capacity of an element.
• The valency of an element is determined by the number of electrons in its outermost shell.
• Atomic Mass:
• The atomic mass of an element is the average mass of all its isotopes, taking into account their relative abundance.
• All matter is made up of small particles called atoms.
• Atoms are indivisible and indestructible.
• All atoms of a given element are identical in mass and properties.
• Compounds are formed when atoms of different elements combine in fixed ratios.
• Discovery of Subatomic Particles:
• Electrons were discovered by J.J. Thomson using the cathode ray tube experiment.
• Protons were discovered by E. Goldstein using the anode ray experiment.
• Neutrons were discovered by J. Chadwick using the neutron scattering experiment.
• Properties of Subatomic Particles:
• Electrons are negatively charged and have a negligible mass.
• Protons are positively charged and have a mass of 1 atomic mass unit (amu).
• Neutrons have no charge and have a mass of 1 amu.
• Structure of an Atom:
• An atom consists of a positively charged nucleus at the center and negatively charged electrons revolving around the nucleus in circular orbits.
• The number of protons in the nucleus determines the atomic number of an element.
• The total number of protons and neutrons in the nucleus determines the mass number of an element.
• Isotopes are atoms of the same element with the same atomic number but different mass numbers.
• Atomic Models:
• Rutherford's nuclear model of the atom proposed that most of the mass of an atom is concentrated in its nucleus and electrons revolve around the nucleus in circular orbits.
• Bohr's model of the atom proposed that electrons revolve around the nucleus in fixed circular orbits at different energy levels.
• Valency:
• Valency is the combining capacity of an element.
• The valency of an element is determined by the number of electrons in its outermost shell.
• Atomic Mass:
• The atomic mass of an element is the average mass of all its isotopes, taking into account their relative abundance.
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