7th Std Science Term 1 Solution in English | Lesson.4 Atomic Structure

Lesson 4. Atomic Structure

Atomic Structure Book Back Solution 2021 - 2022

Lesson 4. Atomic Structure

I . Choose the correct answer.

1. The basic unit of matter is ________

  1. Element
  2. Atom
  3. Molecule
  4. Electron

Ans : Atom

2. The subatomic particle revolve around the nucleus is _______

  1. Atom
  2. Neutron
  3. Electron
  4. Proton

Ans : Electron

3. _______ is positively charged

  1. Proton
  2. Electron
  3. Molecule
  4. Neutron

Ans : Proton

4. The atomic number of an atom is _____

  1. Number of neutrons
  2. Number of protons
  3. Total number of protons and neutrons
  4. Number of atoms

Ans : Number of protons

5. _______________ Nucleons comprises of

  1. Protons and electrons
  2. Neutrons and electrons
  3. Protons and neutrons
  4. Neutrons and Positron

Ans : Protons and neutrons

II. Fill in the blanks:

1. The smaller particles found in the atom is called _________________.

Ans : Subatomic particles. 

2. The nucleus has __________________ and _______________ .

Ans : protons and neutrons

3. The _______________ revolve around the nucleus.

Ans : electrons

4. If the valency of carbon is 4 and that of hydrogen is 1 , then the molecular formula of methane is_________________ .

Ans : CH4

5. There are two electrons in the outermost orbit of the magnesium atom. Hence, the valency of magnesium is_______________ .

Ans : 2

III. Match the following:

1. Valency Fe
2. Neutral Particle Proton
3. Iron Electrons in the outermost Orbit
4. Hydrogen Neutron
5. Positively charged Particle Monovalent
Ans : 1 – C, 2 – E, 3 – A, 4 – B, 5 – D

IV. True of False.

1. The basic unit of an element is molecule.

Ans : False

Cu. An. : The basic unit of an element is atoms.

2. The electrons are positively charged.

Ans : False

Cu. An. : The electrons are negatively charged.

3. An atom is electrically neutral.

Ans : True.

4. The nucleus is surrounded by protons

Ans : False 

Cu. An : The nucleus is surrounded by protons

V. Complete the analogy.

1. Sun: Nucleus, planets: ________________.

Ans : Electrons

2. Atomic number: ________________, Mass number: number of protons and neutrons.

Ans : number of protons or electrons 

3. K: Potassium, C: ____________________.

Ans : Corban 

VI. Assertion and reason:

1. Assertion : An atom is electrically neutral.

Reason : Atoms have equal number of protons and electrons.

Answer : Both are true and Reason is the correct explanation of Assertion.

2. Assertion : The mass of an atom is the mass of its nucleus.

Reason : The nucleus is at the centre.

Answer : Both are true and Reason is the correct explanation of Assertion.

3. Assertion : The number of protons or the number of neutrons is known as atomic number.

Reason : The mass number is the sum of protons and neutrons.

Answer : Assertion is false but the Reason is true statement.

Correct statement : The number of protons and neutrons is mass number.

VII. Give very short answer:

1. Define – A atom.

The atom is the smallest particles of a chemical element that retains its chemical properties.

2. Name the sub-atomic particles.

Proton, Electron, Neutrons.

3. What is atomic number?

The number of electrons or protons in an atom is called the atomic number of that atom. It is denoted by the letter Z.

4. What are the characteristics of proton?

The proton is the positively charged particle and it’s located in the nucleus. It positive charge is of the same magnitude as that of the electron’s negative charge.

5. Why neutrons called neutral particles?

Neutrons are the particles in an atom that have a neutral change. They are not positive like protons. They are not negative like electrons. So they are called as neutral particles.

VIII. Answer briefly

1. Distinguish Isotopes from Isobar.

Isotopes Isobar
Isotopes are atoms of the same element thus have same atomic number but different mass number. Isobar is such atoms which have same mass number but different atomic numbers. Thus isobars are different elements.
Ex. Hydrogen has three isotopes protium with deuterium, tritium atomic number 1 but mass number 1,2,3. Ex. Calcium and Argon are isobar as they have atomic number 20 and 18 but their mass number is 40.

2. What are isotones? Give one example.

Isotones are the atoms of different elements with same number of neutrons.

13 C6 Neutrons = 13 – 6 = 7

14 C7 Neutrons = 14 – 7 = 7

3. Differentiate mass number from atomic number.

Elements Compounds
1. The number of electrons or protons in an atoms is called atomic of that atom. The number of protons and neutrons present is its nucleus is called mass number of atom.
2. It is denoted by Z. It is denoted by A.
Ex. Helium has 2 protons and two electrons. hence its atomic number will be 2 Ex. Sodium has 11 protons and 12 neutrons. hence its mass number A = 11 + 12 = 23

4. The atomic number of an element is 9. It has 10 neutrons. Find the element from the periodic table. What will be its mass number? 

The element is Fluorine. Its mass number A=n + p = 10 + 9 = 19

Mass number of Fluorine = 1

IX. Answer in detail:

1. Draw the structure of an atom and explain the position of the sub-atomic particles.

Structure of an atom

Position of the subatomic

Particles : 1. Protons, 2. Electrons, 3. Neutrons

  • The nucleus of atom contains the protons and neutrons.
  • The outermost regions of the atom are called electron shells and contain the electrons
  • The protons have positive charge white neutrons have a neutral charge.
  • Electrons circle around the nucleus of an atom they are negatively charged.

2. The atomic number and the mass number of an element is 26 and 56 respectively. Calculate the number of electrons protons and neutrons in its atom. Draw the structure.

Atomic number Z = 26
Mass number A = 56
No. of protons P = ?
No. of electrons = ?
No. of neutron N = ?
Name of the element is iron (Fe)
No. of proton (P) = 26
Mass number A = n + p
56 = n + p
n = 56 – 26
No. of neutrons, n = 30
In an element No. of protons an No. of electrons = No. of protons = 26

Structure of iron:

அணு அமைப்பு பாட வினா மற்றும் விடைகள் - 2021

(Fe = 2, 8, 14, 2)

3. What are nucleons? Why are they called so? Write the properties of the nucleons?

Nucleons are sub-atomic particles which are located in the nucleus of atoms.’

Neutron and proton exist within the nucleus of the atom together they are called as nucleons

Properties of Nucleons:

  • Nucleons have same mass as if they were identical particles that differ only in their electric charge.
  • The proton carries a charge +1 and the neutrons are neutral.
  • The size nucleon is about 1:6 fm (Femto meters)
  • The force that holds the nucleus together is very short range.

4. Define valency? What is the valency of the element with atomic number 8? What is the compound by the element with hydrogen?

(i). Valency is defined as the combining capacity of an element.

(ii). Valency of the element with atomic number : 8

Name of the element: oxygen : 0

Atomic number : 8

Valency : 2

Water (H2O) is the oxide of hydrogen and most familiar oxygen compound.


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