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Chapter 4 ATOMIC STRUCTURE

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 ICSE CHEMISTRY CLASS 8

Atomic Structure: ICSE Class 8 Syllabus

Introduction to Atomic Structure: Atomic structure refers to the organization and arrangement of subatomic particles within an atom. Understanding the atomic structure is crucial to comprehend the behavior and properties of matter. In ICSE Class 8, students are introduced to the basic concepts of atomic structure.

Subatomic Particles: Atoms are composed of three main subatomic particles: protons, neutrons, and electrons.

  1. Protons: Protons are positively charged particles found in the nucleus (central core) of an atom. They contribute to the atom's mass and help define its identity (atomic number). Protons are denoted by the symbol 'p' or 'p+'.

  2. Neutrons: Neutrons are neutral particles also located in the nucleus. They add to the atomic mass without affecting the element's chemical properties. Neutrons are represented by the symbol 'n'.

  3. Electrons: Electrons are negatively charged particles that orbit around the nucleus in energy levels or shells. They determine the atom's chemical behavior and are responsible for its size. Electrons are denoted by 'e-'.

Atomic Number and Mass Number:

  1. Atomic Number (Z): The atomic number represents the number of protons in the nucleus. It determines the element's identity. For example, all carbon atoms have an atomic number of 6.

  2. Mass Number (A): The mass number is the sum of protons and neutrons in an atom's nucleus. It is represented as A = Z + N, where N is the number of neutrons.


Isotopes: Isotopes are atoms of the same element with the same number of protons (same atomic number) but different numbers of neutrons (different mass numbers). This leads to variations in atomic mass. Isotopes may have slightly different physical properties but similar chemical behavior.


Electronic Configuration: The arrangement of electrons in an atom's energy levels is known as its electronic configuration. The electronic configuration determines an element's chemical properties and its position in the periodic table.

Bohr's Model of the Atom: Niels Bohr proposed a simplified model of the atom in which electrons move in fixed circular orbits around the nucleus. Each orbit has a specific energy level, and electrons can jump between orbits by absorbing or emitting energy in the form of photons.


Valence Electrons and the Periodic Table: Valence electrons are the electrons present in the outermost energy level of an atom. They are responsible for an element's chemical reactivity and bonding. The periodic table is organized based on the increasing atomic number and electron configuration, which leads to the arrangement of elements with similar properties in groups and periods.


Summary: The atomic structure is a fundamental concept in chemistry that explains the composition and behavior of matter at the smallest scale. Understanding subatomic particles, atomic number, mass number, isotopes, electronic configuration, and the periodic table lays the foundation for comprehending chemical reactions and the properties of different elements.


Questions :


Here are some questions and answers related to atomic structure based on the ICSE Class 8 syllabus:

Q1: What are subatomic particles? Name the three main subatomic particles and mention their charges.


A1: Subatomic particles are the tiny constituents that make up atoms. The three main subatomic particles are:

  • Protons (p+): Positively charged particles found in the nucleus.

  • Neutrons (n): Neutral particles also located in the nucleus.

  • Electrons (e-): Negatively charged particles orbiting around the nucleus.


Q2: Define atomic number and mass number. How are they different?


A2:

  • Atomic Number (Z): It represents the number of protons in an atom's nucleus. It defines the element's identity and determines its position in the periodic table.

  • Mass Number (A): It is the sum of protons and neutrons in an atom's nucleus. It contributes to the atom's mass but does not affect its chemical properties. Mass number = Atomic number (Z) + Number of neutrons (N).


Q3: Explain isotopes. Provide an example of an element with isotopes.


A3: Isotopes are atoms of the same element that have the same number of protons (same atomic number) but different numbers of neutrons (different mass numbers). This results in variations in atomic mass. For example, carbon has isotopes carbon-12 (6 protons, 6 neutrons) and carbon-14 (6 protons, 8 neutrons).


Q4: Describe the concept of valence electrons. How do valence electrons influence an element's chemical behavior?


A4: Valence electrons are the electrons present in the outermost energy level (valence shell) of an atom. They play a crucial role in determining an element's chemical behavior and reactivity. The number of valence electrons influences an element's ability to form bonds with other elements and participate in chemical reactions.


Q5: Explain Bohr's model of the atom. How does it describe the arrangement of electrons?


A5: Bohr's model suggests that electrons move in fixed circular orbits around the nucleus. Each orbit represents a specific energy level. Electrons can transition between orbits by absorbing or emitting energy in discrete amounts. This model explains how electrons have quantized energy levels and helped refine the understanding of atomic structure.


Q6: What is the significance of the periodic table in understanding atomic structure?


A6: The periodic table organizes elements based on their increasing atomic numbers and electron configurations. It provides a systematic way to understand the relationships between elements and predict their properties. Elements with similar electron configurations exhibit similar chemical behavior and are grouped together in columns (groups) and rows (periods) on the periodic table.


Q7: Compare and contrast protons, neutrons, and electrons in terms of their charges and locations within an atom.


A7:

  • Protons: Positively charged particles, located in the nucleus.

  • Neutrons: Neutral particles, also in the nucleus.

  • Electrons: Negatively charged particles, orbiting the nucleus in energy levels.

Q8: How do isotopes of an element differ? Provide an example of an isotope and explain why it has a different mass number.


A8: Isotopes of an element have the same number of protons (same atomic number) but different numbers of neutrons (different mass numbers). For instance, hydrogen has isotopes like hydrogen-1 (1 proton, 0 neutrons) and hydrogen-2 (1 proton, 1 neutron) due to varying neutron counts.


Q9: Explain how the electronic configuration of an atom influences its chemical behavior.


A9: The electronic configuration determines the distribution of electrons in different energy levels. It affects an element's reactivity by determining how easily electrons can be gained, lost, or shared in chemical reactions. Elements with similar electronic configurations often display similar chemical properties.


Q10: What is the relationship between atomic number, atomic mass, and the number of protons and neutrons in an atom?


A10: Atomic number is equal to the number of protons in an atom. Atomic mass is the sum of protons and neutrons. Atomic mass - Atomic number gives the number of neutrons. The arrangement of protons, neutrons, and electrons defines the atom's identity, behavior, and properties.

Remember that these questions and answers are based on the ICSE Class 8 syllabus, and you should refer to your official textbooks and materials for the most accurate and comprehensive information.


Short Questions and Answers


Q1: What are subatomic particles?

A1: Subatomic particles are the tiny components that make up atoms. They include protons, neutrons, and electrons.


Q2: What is the role of protons in an atom?

A2: Protons are positively charged particles found in the nucleus of an atom. They contribute to the atom's mass and determine its identity.


Q3: Define atomic number.

A3: The atomic number is the number of protons in an atom's nucleus. It identifies the element and its position in the periodic table.


Q4: What is an isotope?

A4: Isotopes are atoms of the same element with the same number of protons (atomic number) but different numbers of neutrons (mass number).


Q5: Explain the concept of valence electrons.

A5: Valence electrons are electrons in the outermost energy level of an atom. They influence an element's chemical reactivity and bonding.


Q6: Who proposed the Bohr model of the atom?

A6: Niels Bohr proposed the Bohr model, which depicts electrons in fixed orbits around the nucleus.


Q7: How do electrons move in Bohr's model of the atom?

A7: Electrons move in fixed circular orbits at different energy levels around the nucleus.


Q8: What is the significance of the periodic table?

A8: The periodic table organizes elements based on their atomic numbers and electron configurations, helping predict their properties.


Q9: What determines an element's position in the periodic table?

A9: An element's atomic number and electron configuration determine its position in the periodic table.


Q10: What is the relationship between atomic number and the number of protons?

A10: Atomic number is equal to the number of protons in an atom.


Q11: How do isotopes of an element differ?

A11: Isotopes have the same number of protons but different numbers of neutrons.


Q12: How are mass number and atomic number related?

A12: Mass number is the sum of protons and neutrons. Atomic number is the number of protons.


Q13: What is the charge of an electron?

A13: An electron carries a negative charge.


Q14: Where are neutrons located in an atom?

A14: Neutrons are found in the nucleus of an atom.


Q15: What are valence electrons responsible for?

A15: Valence electrons are responsible for an element's chemical reactivity and bonding.


MCQ type Questions


Here are 10 multiple-choice questions (MCQs) based on the ICSE Class 8 syllabus, along with their answers:

Question 1: What is the smallest particle of an element that retains its properties?

a) Proton

b) Neutron

c) Electron

d) Nucleus

Answer: c) Electron


Question 2: Which subatomic particle is responsible for the identity of an element?

a) Neutron

b) Electron

c) Proton

d) Photon

Answer: c) Proton


Question 3: The number of protons in an atom determines its:

a) Atomic mass

b) Mass number

c) Atomic number

d) Valence electrons

Answer: c) Atomic number


Question 4: Isotopes of an element have the same number of:

a) Neutrons

b) Electrons

c) Protons

d) Valence electrons

Answer: c) Protons


Question 5: Which of the following particles has a negative charge?

a) Proton

b) Neutron

c) Electron

d) Nucleus

Answer: c) Electron


Question 6: Which scientist proposed the planetary model of the atom?

a) Rutherford

b) Bohr

c) Dalton

d) Mendeleev

Answer: b) Bohr


Question 7: The outermost energy level of an atom is known as the:

a) Nucleus

b) Valence shell

c) Electron cloud

d) Neutron level

Answer: b) Valence shell


Question 8: What is the sum of protons and neutrons in an atom's nucleus called?

a) Atomic number

b) Mass number

c) Valence number

d) Electron number

Answer: b) Mass number


Question 9: Elements with similar electronic configurations are placed in the same:

a) Group

b) Period

c) Row

d) Shell

Answer: a) Group


Question 10: What determines the chemical properties of an element?

a) Atomic mass

b) Number of neutrons

c) Number of protons

d) Number of electrons

Answer: d) Number of electrons

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