Practice Worksheets for Class 8 Science: Atomic Structure
Access printable practice worksheets for Atomic Structure designed to align with the 2026-27 academic syllabus for Class 8 Science. These structured exercises help students evaluate their conceptual understanding and improve exam readiness.
Practice Atomic Structure Worksheets for Class 8 Science
Access the complete worksheet PDF for Atomic Structure below. Regular practice with these targeted questions builds familiarity with standard exam patterns and helps secure higher marks in final Science evaluations.
A. Check Point
1. What is an atom?
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Answer: An atom is the smallest particle of an element that takes part in a chemical reaction.
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2. Define molecule.
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Answer: A molecule is the smallest particle of an element or compound that can exist freely, made of two or more atoms joined together.
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3. Why are atoms called the building blocks of matter?
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Answer: All matter is made of atoms, just as a wall is made of bricks.
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4. Name the scientists who gave models of the atom.
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Answer: John Dalton, J.J. Thomson, Ernest Rutherford and Niels Bohr (and James Chadwick, who discovered the neutron).
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5. Describe the main postulates of Dalton's atomic theory.
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Answer: Matter is made of tiny indivisible particles called atoms. Atoms of one element are identical in mass and properties. Atoms of different elements differ. Atoms combine in simple whole-number ratios to form compounds. Atoms can neither be created nor destroyed in a chemical reaction.
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6. Fill in the blanks: 1. The three fundamental particles are ____, ____ and ____. 2. The charge on proton and electron is ____ and ____; the neutron has ____ charge. 3. ____ suggested the heavy positively charged nucleus. 4. The electron was discovered by ____ and the neutron by ____. 5. The nucleus is composed of ____ and ____.
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Answer: 1. protons, neutrons and electrons; 2. positive, negative, no (zero); 3. Rutherford; 4. J.J. Thomson, James Chadwick; 5. protons, neutrons.
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1. What are atomic number and mass number?
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Answer: Atomic number is the number of protons in the nucleus of an atom. Mass number is the total number of protons and neutrons in the nucleus.
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2. The atomic number of an element is 8. What does it tell you?
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Answer: The atom has 8 protons and, if neutral, 8 electrons. The configuration is 2, 6, and the element is oxygen.
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3. Atomic number 92, mass number 238: find the particles.
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Answer: Protons = 92, electrons = 92, neutrons = 238 - 92 = 146 (uranium).
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10. True or False: 1. Removing or adding electrons forms ions. 2. Loss of electrons gives negative ions. 3. Positive and negative ions combine to form ionic compounds. 4. Gain of electrons gives negative ions.
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Answer: 1. True; 2. False (loss gives positive ions); 3. True; 4. True.
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B. Keywords
11. Define: anion, cation, chemical bond, isotopes, valency, valence electrons, valence shell.
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Answer: Anion: a negatively charged ion. Cation: a positively charged ion. Chemical bond: the force that holds atoms together in a compound. Isotopes: atoms of the same element with the same atomic number but different mass numbers. Valency: the combining capacity of an atom. Valence electrons: electrons in the outermost shell. Valence shell: the outermost shell of an atom.
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C. Exercise
(i) The fundamental particles are (a) electrons (b) protons (c) neutrons (d) electrons, protons and neutrons
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Answer: (d).
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(ii) The electron was discovered by (a) J.J. Thomson (b) Rutherford (c) Dalton (d) Bohr
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Answer: (a) J.J. Thomson.
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(iii) The neutron was discovered by (a) Rutherford (b) James Chadwick (c) Goldstein (d) Thomson
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Answer: (b) James Chadwick.
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(iv) The nuclear model was proposed by (a) Rutherford (b) Bohr (c) Thomson (d) Goldstein
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Answer: (a) Rutherford.
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(v) The maximum number of electrons in an orbit is (a) 2n2 (b) 2n2+1 (c) 2n (d) none
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Answer: (a) 2n2 (n is the shell number).
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(vi) The number of electrons in the outermost orbit to follow the octet rule is (a) 8 (b) 4 (c) 16 (d) 5
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Answer: (a) 8.
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18. Fill in the blanks: 1. Rutherford showed that ____ rays come out of unstable nuclei. 2. Electrons revolve in fixed paths called ____. 3. The number of protons plus neutrons is its ____. 4. Atomic number is the number of ____ in the nucleus. 5. ____ is the combining capacity of an atom.
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Answer: 1. alpha; 2. orbits (shells); 3. mass number; 4. protons; 5. Valency.
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D. Tables and Numerical Questions
1. An atom usually contains three main particles. Complete the table.
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Answer:
| Particle | Charge |
|---|---|
| Proton | Positive (+1) |
| Neutron | None (neutral) |
| Electron | Negative (-1) |
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2. Write the electronic configuration of elements whose atomic numbers are given.
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Answer: The atomic numbers were in a table that is not in the text. Use this rule: fill shells 2, 8, 8 in order. For example, Z = 3 gives 2,1; Z = 9 gives 2,7; Z = 11 gives 2,8,1; Z = 17 gives 2,8,7.
Teacher's Note: The values of A to D were not printed in the extracted text; apply the rule above.
3. Particles A (3 protons, 4 neutrons, 2 electrons), B (9, 10, 10), C (17, 18, 17), D (17, 20, 17). a. Which is a cation, an anion, a pair of isotopes? b. Formula of C with hydrogen. c. Formula of the compound of A and B.
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Answer: a. A is the cation (3 protons, only 2 electrons: Li+), B is the anion (9 protons, 10 electrons: F-), and C and D are isotopes (same 17 protons, different neutrons). b. C is chlorine, so HCl. c. A is lithium (Li+) and B is fluoride (F-), so LiF.
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4. Chlorine has atomic number 17 and isotopes with mass numbers 35 and 37. (a) What is atomic number? (b) Electronic configuration of chlorine? (c) Complete the table of isotopes.
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Answer: (a) The number of protons in the nucleus. (b) 2, 8, 7. (c) Cl-35: 17 protons, 17 electrons, 18 neutrons. Cl-37: 17 protons, 17 electrons, 20 neutrons.
Teacher's Note: Neutrons = mass number - atomic number.
5. Elements A to E: (neutrons, protons, electrons) A 22,18,18; B 18,17,17; C 10,9,9; D 7,7,7; E 20,17,17. Choose (a) a pair of isotopes (b) the element with mass number 19 (c) the element with mass number 37.
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Answer: Mass number = neutrons + protons: A = 40, B = 35, C = 19, D = 14, E = 37. (a) B and E (both have 17 protons); (b) C; (c) E.
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E. True or False
1. The atom is an indivisible particle. 2. The neutron has a positive charge. 3. The nucleus contains the mass of the atom. 4. All hydrogen atoms have the same atomic number and mass number. 5. Loss of electrons gives a positive ion. 6. The combining capacity of aluminium is 3.
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Answer: 1. False; 2. False; 3. True (almost all the mass); 4. False (isotopes differ in mass number); 5. True; 6. True.
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F. Define
25. Define: atom, molecule, atomic number, mass number, isotope.
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Answer: Atom: the smallest particle of an element. Molecule: a group of atoms bonded together. Atomic number: the number of protons in the nucleus. Mass number: the total of protons and neutrons. Isotope: atoms of the same element with different mass numbers.
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G. Answer the Following
1. Write the fundamental particles and describe each in one line.
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Answer: Proton: a positively charged particle in the nucleus. Neutron: a neutral particle in the nucleus. Electron: a negatively charged, very light particle revolving around the nucleus.
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2. What is atomic number? Write the atomic number of the first five elements.
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Answer: The number of protons in an atom. Hydrogen 1, helium 2, lithium 3, beryllium 4, boron 5.
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3. What is atomic mass?
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Answer: The mass of an atom, mostly from the protons and neutrons in the nucleus; it is approximately equal to the mass number.
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4. An atom has 4 protons, 5 neutrons and 4 electrons. Give its atomic number and mass number.
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Answer: Atomic number = 4; mass number = 4 + 5 = 9 (beryllium).
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5. Draw atomic structures of sodium (11, 23), chlorine (17, 35) and carbon (6, 12).
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Answer: Sodium has 11 protons and 12 neutrons, chlorine has 17 protons and 18 neutrons, and carbon has 6 protons and 6 neutrons.
Teacher's Note: The diagrams are below.
6. What are isotopes? Give an example.
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Answer: Atoms of the same element with the same atomic number but different mass numbers. Example: chlorine-35 and chlorine-37 (or hydrogen, deuterium and tritium).
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7. Why can we write the electronic configuration if we know the atomic number?
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Answer: The atomic number tells the number of protons, which equals the number of electrons in a neutral atom, and electrons are filled shell by shell in a fixed pattern (2, 8, 8).
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8. What is the electronic configuration, atomic number and mass number of Na+?
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Answer: Na has configuration 2,8,1. Na+ has lost one electron, so it is 2,8. Atomic number is still 11 and mass number is still 23.
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9. Which is chemically more reactive, element X (atomic number 18) or Z (atomic number 16)?
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Answer: Z (16) is more reactive. Its configuration is 2,8,6, so it needs two electrons to complete its octet. X (18) is 2,8,8, which is a full outer shell, so it is inert (argon).
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10. The electronic configurations of X and Y are given; when they form a compound, give the mass of one mole of the compound.
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Answer: The configurations were shown as a figure that is not in the text, so the final number cannot be computed here. To solve it, find the atomic numbers from the configurations, add the atomic masses of the atoms in the formula and write the answer in grams.
Teacher's Note: I am not able to give the number without the figure; please check the worksheet.
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Atomic Structure Practice Sheet and Solutions for Class 8 Science
Atomic Structure Printable Worksheet for Class 8 Science
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FAQs
You can download the teacher-verified PDF for CBSE Class 8 Science Atomic Structure Worksheet Set 01 from StudiesToday.com. These practice sheets for Class 8 Science are designed as per the latest CBSE academic session.
Yes, our CBSE Class 8 Science Atomic Structure Worksheet Set 01 includes a variety of questions like Case-based studies, Assertion-Reasoning, and MCQs as per the 50% competency-based weightage in the latest curriculum for Class 8.
Yes, we have provided detailed solutions for CBSE Class 8 Science Atomic Structure Worksheet Set 01 to help Class 8 and follow the official CBSE marking scheme.
Daily practice with these Science worksheets helps in identifying understanding gaps. It also improves question solving speed and ensures that Class 8 students get more marks in CBSE exams.
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