Atomic Structure Book Back Questions 8th Science Lesson 12
8th Science Lesson 12
12] Atomic Structure
Book Back Questions with Answer and Do You Know Box Content
Do You Know?
John Dalton, son of a poor weaver, began his career as a village school teacher at the age of 12. He became the principal of the school seven years later. In 1793, he moved to Manchester to teach Physics, Chemistry and Mathematics in a college. He proposed his atomic theory in 1803. He carefully recorded each day, the temperature, pressure and amount of rainfall from his youth till the end. He was a meticulous meteorologist.
The fact that air is a poor conductor of electricity is a blessing in disguise for us. Imagine what would happen if air had been a good conductor of electricity. All of us would have got electrocuted, when a minor spark was produced by accident.
Electricity, when passes through air, removes the electrons from the gaseous atoms and produces cations. This is called electrical discharge.
In television tube cathode rays are deflected by magnetic fields. A beam of cathode rays is directed toward a coated screen on the front of the tube, where by varying the magnetic field generated by electromagnetic coils, the beam traces a luminescent image.
When hydrogen gas was taken in a discharge tube, the positively charged particles obtained from the hydrogen gas were called protons. Each of these protons are produced when one electron is removed from one hydrogen atom. Thus, a proton can be defined as an hydrogen ion (H+). H 🡪 H+ + e–
When invisible radiation falls on materials like zinc sulphide, they emit a visible light (or glow). These materials are called fluorescent materials.
Choose the best answers:
1. The same proportion of carbon and oxygen in the carbon dioxide obtained from different sources proves the law of _______________.
(a) Reciprocal proportion
(b) Definite proportion
(c) Multiple proportion
(d) Conservation proportion
2. Cathode rays are made up of
(a) Neutral particles
(b) Positively charged particles
(c) Negatively charged particles
(d) None of the above
3. In water, hydrogen and oxygen are combined in the ratio of ____________ by mass.
(a) 1:8
(b) 8:1
(c) 2:3
(d) 1:3
4. Which of the following statements made by Dalton has not undergone any change?
(a) Atoms cannot be broken
(b) Atoms combine in small, whole numbers to form compounds
(c) Elements are made up of atoms
(d) All atoms of an elements are alike
5. In all atoms of an element
(a) The atomic and the mass number are same
(b) The mass number is same and the atomic number is different
(c) The atomic number is same and the mass number is different
(d) Both atomic and mass numbers may vary
Fill in the blanks:
1. _______________ is the smallest particle of an element.
2. An element is composed of ____________ atoms.
3. An atom is made up of ___________, ______________ and _______________.
4. A negatively charged ion is called _____________, while positively charged ions is called ______________.
5. _____________ is a negatively charged particle (Electron/Proton).
6. Proton is deflected towards the _________ charged plate (positively, negatively).
Match the following:
1. Law of conservation of mass – Sir William Crookes
2. Law of constant proportion – James Chadwick
3. Cathode rays – Joseph Proust
4. Anode rays – Lavoisier
5. Neutrons – Goldstein
Answers:
Choose the best answers:
1. definite proportion 2. negatively charged particles 3. 1:8 4. All atoms of an elements are alike
5. the atomic and the mass number are same
Fill in the blanks:
1. Atom 2. Same kind of 3. Proton, electron, Neutron 4. Anion, Cation 5. Electron 6. Negatively
Match the following:
1. Law of conservation of mass- Lavoisier
2. Law of constant proportion- Joseph Proust
3. Cathode rays- Sir William Crookes
4. Anode rays- Goldstein
5. Neutrons- James Chadwick