Atomic Foundations of Matter Class 9 Worksheet with Answers Science Chapter 9

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Class 9 Atomic Foundations of Matter Worksheet

Worksheet On Atomic Foundations of Matter Class 9

Atomic Foundations of Matter Worksheet Class 9

→ Octet Rule: Atoms tend to gain, lose, or share electrons to achieve eight electrons in their outermost shell.

→ Element: A pure substance made up of only one type of atom.

→ Compound: A substance formed when two or more elements combine chemically in a fixed ratio.

→ Physical Change: A change in which no new substance is formed and only physical properties change.

→ Chemical Change: A change in which new substances with different properties are formed.

→ Solution: A homogeneous mixture in which one substance is dissolved in another.

→ Mixture: A combination of substances that are not chemically combined and can be separated by physical means.

→ Effervescence: The bubbling or fizzing caused by the release of a gas during a chemical reaction.

→ Law of Conservation of Mass: Mass can neither be created nor destroyed in a chemical reaction; therefore, the total mass remains constant.

→ Reactants: Substances that take part in a chemical reaction.

→ Products: Substances formed as a result of a chemical reaction.

→ Precipitate: An insoluble solid formed during a chemical reaction in a solution.

→ Law of Constant Proportions (Definite Proportions): A compound always contains the same elements combined in a fixed ratio by mass.

→ Dalton’s Atomic Theory: A theory stating that matter is made of atoms, which are indivisible and combine in simple whole-number ratios to form compounds.

→ Molecule: An electrically neutral group of two or more atoms bonded together that can exist independently and shows all the properties of that substance.

→ Neutral Entity: A particle (like a molecule) having no overall charge.

→ Chemical Bond: The force of attraction that holds atoms together in a molecule or compound.

→ Covalent Bond: A bond formed by sharing of electrons between atoms.

→ Single Bond: A bond formed between two atoms by sharing one pair of electrons.

→ Double Bond: A bond formed between two atoms by sharing two pairs of electrons.

→ Covalent Compound: A compound formed by interaction between atoms through a shared pair of electrons.

→ Ionic Bond: A bond formed by the transfer of electrons from one atom to another, resulting in oppositely charged ions.

→ Ion: A charged particle formed by the loss or gain of electrons.

→ Cation: A positively charged ion formed by the loss of electrons.

→ Anion: A negatively charged ion formed by the gain of electrons.

→ Ionic Compound: A compound formed due to the electrostatic force of attraction between oppositely charged ions.

→ Electrostatic Force of Attraction: The force that holds oppositely charged ions together.

→ Crystal Lattice: A regular, repeating three-dimensional arrangement of ions in an ionic compound.

→ Polyatomic Ion: An ion formed by the combination of atoms of two or more elements.

→ Chemical Formula: A symbolic representation of a compound showing the elements present and their ratios.

→ Electrical Conductivity: The ability of a substance to conduct electricity.

→ Atomic Mass: The mass of an atom, usually expressed in atomic mass units (u).

→ Molecular Mass: The sum of the atomic masses of all the atoms in a molecule.

→ Formula Unit: The simplest whole-number ratio of ions in an ionic compound.

→ Formula Unit Mass: The sum of atomic masses of all atoms present in a formula unit of an ionic compound.

Class 9 Science Exploration Chapter 9 Worksheet

Class 9 Science Atomic Foundations of Matter Worksheet

A. Multiple Choice Questions

Question 1.
Which of the following is an ionic compound?
(a) CH₄
(b) CCl₄
(c) NH₃
(d) NaCl

Question 2.
Who proposed the Law of Conservation of Mass?
(a) John Dalton
(b) Joseph Proust
(c) Antoine Lavoisier
(d) Rutherford

Question 3.
Which of the following correctly represents a compound formed by Mg²⁺ and Cl^–
(a) MgCl
(b) MgCl₂
(c) Mg₂Cl
(d) Mg₂Cl₂

Question 4.
Which of the following is NOT a compound?
(a) Water
(b) Carbon dioxide
(c) Oxygen
(d) Sodium

Question 5.
This question consists of an Assertion (A) and a Reason (R). Read the Assertion and Reason and choose the appropriate answer.
Assertion (A): Sugar solution does not conduct electricity.
Reason (R): Sugar does not form ions in solution.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.

Question 6.
This question consists of an Assertion (A) and a Reason (R). Read the Assertion and Reason and c the appropriate answer.
Assertion (A): The formula unit represents the simplest ratio of ions in an ionic compound.
Reason (R): Ionic compounds do not exist as single molecules.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.

B. State True (T) or False (F).

Question 1.
The Law of Constant Proportions applies to mixtures.

Question 2.
Covalent compounds form ions in aqueous solutions.

Question 3.
Ionic compounds can conduct electricity when dissolved in water.

Question 4.
The formula H₂O indicates two oxygen atoms and one hydrogen atom.

Question 5.
Chlorine forms an anion by gaining an electron.

Question 6.
Atoms combine in fractional ratios to form compounds.

Question 7.
Cations and anions are collectively called ions.

C. Fill in the blanks.

Question 1.
In an open system, mass appears to decrease because escapes.

Question 2.
If atoms could combine in any ratio, compounds would not have composition.

Question 3.
Sodium loses one electron to form a ion.

Question 4.
The force holding ions together is called force of attraction.

Question 5.
The Law of Constant Proportions was proposed by .

Question 6.
The gas produced when baking soda reacts with vinegar is .

Question 7.
The force that holds atoms together is called a bond.

Question 8.
Dalton’s Atomic Theory states that atoms are particles.

D. Assign one word to the following.

Question 1.
The smallest particle of an element.

Question 2.
A positively charged ion.

Question 3.
A negatively charged ion.

Question 4.
Bond formed by the sharing of electrons.

Question 5.
Bond formed by transfer of electrons.

Question 6.
A group of atoms carrying a charge.

Question 7.
An electrically neutral group of atoms.

E. Match the Columns.

Question 1.
Match the polyatomic ions given in Column I with their formulae given in Column II.

Column I	Column II
(i) Hydroxide	(a) \(\mathrm{HCO}_3^{-}\)
(ii) Nitrate	(b) \(\mathrm{SO}_4^{2-}\)
(iii) Sulphate	(c) OH–
(iv) Carbonate	(d) \(\mathrm{NH}_4^{+}\)
(v) Ammonium	(e) \(\mathrm{CO}_3^{2-}\)
(vi) Hydrogencarbonate	(f) \(\mathrm{NO}_3^{-}\)

Question 2.
Match the compounds given in Column I with their corresponding type of bonds given in Column II

Column I	Column II
(i) H2	(a) Double covalent bond
(ii) O	(b) Single covalent bond
(iii) NaCl	(c) Two double bonds
(iv) CO2	(d) Ionic bond

F. Differentiate between the following.

Question 1.
Ionic Compounds and Covalent Compounds

Question 2.
Cations and Anions

G. Very Short Answer Type Questions

Question 1.
What is meant by formula unit mass?

Question 2.
What type of bond is present in CaCl₂?

Question 3.
What is meant by the term chemical formula?

H. Short Answer Type Questions

Question 1.
What is a molecule? Give an example.

Question 2.
An element ‘X’ has valency 3. Write the formula of its:
i. Chloride
ii. Sulphate
iii. Carbonate
iv. Nitrate

Question 3.
Why is it necessary to perform chemical reactions in a closed system to verify the law of conservation of mass?

I. Long Answer Type Questions

Question 1.
Explain how atoms combine to form molecules through covalent bonding with examples.

Question 2.
State and explain the main postulates of Dalton’s Atomic Theory.

Question 3.
In an experiment, 1.288 g of copper oxide was obtained from 1.03 g of copper. In another experiment, 3.672 g of copper oxide is obtained on reduction of 2.938 g of copper. Show that this data verifies the law of constant proportions.

Wonder Why

A. Give reasons for the following.
Question 1.
Mass is conserved even when no residue is left after burning a substance.

Question 2.
Noble gases are generally unreactive.

Question 3.
Atoms combine to form chemical bonds.

Question 4.
Covalent compounds generally have low melting points.

Question 5.
Water does not show the properties of hydrogen and oxygen.

Question 6.
Salt solution conducts electricity, but sugar solution does not.

Question 7.
Ionic compounds form crystal lattices instead of existing as individual molecules.

B. Observe the given figure and answer the following questions.

Question 1.
What type of bond is shown in the diagram?

Question 2.
How many pairs of electrons are shared between the atoms?

Question 3.
What is the stability achieved by oxygen atoms?

Question 4.
Write the formula of the molecule formed.

C. Read the paragraph and answer the following questions.
A crystalline solid was analysed and found to have a highly ordered internal structure. The particles were arranged in a repeating pattern extending in all directions. The solid was hard, had a high melting point, and did not conduct electricity in the solid state. However, when the substance was melted, it allowed the flow of electricity. Scientists explained that the behaviour of the substance depends on the arrangement and mohility of its particles.

Question 1.
What type of solid is described in the passage?

Question 2.
Why does it not conduct electricity in solid state?

Question 3.
Why does it conduct electricity when molten?

Question 4.
What is the internal arrangement of particles called?

Question 5.
Predict whether this substance would be soluble in water. Give a reason.

Question 6.
Would this substance conduct electricity in aqueous solution? Explain.

Question 7.
Why does this substance have a high melting point?

D. Complete the table by writing the formula and chemical name of the compounds formed by combining the given components (elements or polyatomic ions) using their valencies/charges.

E. Read the statements given below and complete them.
Question 1.
Hydrogen burns, oxygen supports burning, but water ________ fire.
· This is because: ________

Question 2.
Mass seems to ________ in some reactions carried out in open containers.
· This is because: __________

Question 3.
Oxygen forms _______ molecules instead of existing as single atoms.
· This is because: _______

Question 4.
Water from rivers, lakes, and oceans becomes chemically after purification.
· This is because:

Learn By Doing

A. Substances show different behaviours in terms of solubility and electrical conductivity. A student takes samples of naphthalene, sodium chloride, calcium chloride, copper sulphate, sugar, and camphor and performs the following steps: Analyse 1
· Checks the solubility of each substance separately in water, kerosene and petrol.
· Tests electrical conductivity in both solid and aqueous states using a simple circuit.
Observe carefully and record the expected observations in the table below.

Compound	Solubility in water	Solubility in kerosene	Solubility in petrol	Electrical Conductivity (Solid State)	Electrical Conductivity (Aqueous Solution)
Naphthalene
Sodium chloride
Calcium chloride
Copper sulphate
Sugar
Camphor

B. Riya conducted an experiment to study whether mass is conserved during a chemical reaction. She took vinegar in a conical flask and added baking soda. In the first trial, she kept the flask open and observed bubbling along with a decrease in mass after the reaction. In the second trial, she fixed a balloon at the mouth of the flask before mixing the substances.
Based on the above experiment, answer the following questions:

Question 1.
What observation indicates that a chemical reaction has taken place?

Question 2.
Identify the gas produced during the reaction.

Question 3.
Why does the mass decrease in the open flask setup?

Question 4.
Why does the mass remain unchanged when a balloon is fixed to the flask?

Question 5.
Which law is demonstrated by this experiment?

Question 6.
Does the decrease in mass in the first trial mean that mass is destroyed? Explain.

C. A student conducts an experiment to verify whether mass is conserved during a chemical reaction. The student takes 10 g of calcium carbonate in a closed container and heats it. On heating, calcium carbonate decomposes to form calcium oxide and carbon dioxide gas. After the reaction is complete, the mass of calcium oxide obtained is found to be 5.6 g.

Based on the above experiment, answer the following questions:
Question 1.
Calculate the mass of carbon dioxide gas formed during the reaction.

Question 2.
Verify whether the Law of Conservation of Mass is obeyed in this experiment.

Question 3.
The student repeats the experiment in an open container and observes a decrease in mass. Explain the reason for this observation.

Question 4.
Why should this experiment be performed in a closed container?

Explore with Curiosity

A. While preparing cement, specific proportions of materials must be followed. Explain how this relates to chemical laws and what could happen if proportions are not maintained.

B. In a laboratory, a salt solution allows electricity to pass through it, while a sugar solution does not. Explain this difference based on the nature of bonding and the particles present in the solutions.

C. When a candle burns completely, it seems to disappear without leaving any residue. Explain what happens to the matter and whether this violates the Law of Conservation of Mass.

D. Two unknown compounds, A and B, are given. Compound A dissolves in water, conducts electricity, and has a high melting point. Compound B also dissolves in water but does not conduct electricity and has a low melting point. What can you infer about the nature of compounds A and B?

E. In a competitive quiz, students are asked to identify the correct name of SFg. Some options given are “sulphur fluoride”, “sulphur hexafluoride”, and “hexasulphur fluoride”. Many students select different apswers due to confusion in prefix usage. Write the correct naming of SFg and discuss the importance of prefixes in representing the structure and composition of covalent compounds.

Suggested Activities

A. Using simple materials like clay, beads, or coloured paper, construct 3D models of molecules such as water (H₂0), carbon dioxide (CO₂), and ammonia (NH₃). Represent atoms using different colours and show bonds using sticks or threads to indicate electron sharing. Label each atom and identify whether the bonds formed are single or double covalent bonds, thereby visualising molecular structure.

B. Prepare simple cards showing common ions such as Na⁺, Ca²⁺, Al³⁺, Cl^–, O^2-, and OH^–. Shuffle and distribute the cards among players. Each player tries to form electrically neutral compounds by matching cations and anions correctly. After forming compounds, write their chemical formulae and verify whether the charges are balanced.

C. Observe common household substances like salt, sugar, water, baking soda, and vinegar. Predict whether each substance contains ionic or covalent compounds and whether it will conduct electricity when dissolved in water. Record your predictions and observations in a table to connect classroom learning with everyday life.

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