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ChemistryClass 9CBSE

Consider an atom with 17 protons, 18 neutrons, and 17 electrons. Identify the element, determine its atomic number and mass number, and state whether it is a neutral atom or an ion.

The element is Chlorine (Cl) because it has 17 protons (atomic number = 17). Its atomic number is 17. Its mass number is 17 (protons) + 18 (neutrons) = 35. Since the number of protons (17) equals the number of electrons (17), it is a neutral atom.

ChemistryClass 9CBSE

Draw a simple diagram representing the atomic structure of an oxygen atom (atomic number 8, mass number 16). Label the nucleus, protons, neutrons, and electrons.

The diagram should show a central nucleus with 8 protons and 8 neutrons. The first electron shell should contain 2 electrons, and the second electron shell should contain 6 electrons. All components should be clearly labeled.

ChemistryClass 9CBSE

Define valency and explain how it is related to the electron configuration of an atom.

Valency is the combining capacity of an element, indicating the number of electrons an atom will gain, lose, or share to achieve a stable electron configuration (usually a full outermost shell). It is determined by the number of electrons in the outermost shell (valence electrons); atoms tend to react to achieve an octet (or duet for hydrogen/helium).

ChemistryClass 9CBSE

Discuss the limitations of Rutherford's nuclear model of the atom that led to the development of Bohr's model.

Rutherford's model could not explain why electrons orbiting the nucleus didn't continuously lose energy and spiral into the nucleus, causing the atom to collapse. It also failed to explain the discrete line spectra observed for elements, suggesting electrons could only exist in specific energy levels.

ChemistryClass 9CBSE

How does the atomic number differ from the mass number? What information does each provide about an atom?

The atomic number (Z) represents the number of protons in an atom's nucleus and uniquely identifies an element. The mass number (A) represents the total number of protons and neutrons in an atom's nucleus. The atomic number tells us the element and the number of electrons in a neutral atom, while the mass number indicates the atom's total nuclear mass.

ChemistryClass 9CBSE

Explain the concept of electron shells (or energy levels) and how electrons are distributed within them according to Bohr's model.

Bohr's model proposes that electrons orbit the nucleus in specific, fixed energy levels called electron shells. Each shell can hold a maximum number of electrons: 2 in the first shell, 8 in the second, and 18 in the third (for the first few elements). Electrons fill the lowest energy shells first.

ChemistryClass 9CBSE

What is an isotope? Provide an example to illustrate your explanation.

Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. This means they have the same atomic number but different mass numbers. For example, Carbon-12 (6 protons, 6 neutrons) and Carbon-14 (6 protons, 8 neutrons) are isotopes of carbon.

ChemistryClass 9CBSE

Describe Rutherford's Gold Foil Experiment and explain how its results led to the proposal of the nuclear model of the atom.

Rutherford's Gold Foil Experiment involved firing alpha particles at a thin sheet of gold foil. Most alpha particles passed straight through, suggesting atoms are mostly empty space. However, a small fraction were deflected at large angles, and some even bounced back, indicating the presence of a small, dense, positively charged nucleus at the center of the atom.

ChemistryClass 9CBSE

Explain the fundamental differences between protons, neutrons, and electrons in terms of their charge, mass, and location within an atom.

Protons have a positive charge (+1), a mass of approximately 1 atomic mass unit (amu), and are located in the nucleus. Neutrons have no charge (neutral), a mass of approximately 1 amu, and are also located in the nucleus. Electrons have a negative charge (-1), a very small mass (approximately 1/1836 amu), and orbit the nucleus in electron shells.

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