Samacheer Kalvi 7th Science Term 1 Unit 3 Book Back Question and Answers:

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Samacheer Kalvi 7th Science Book Back Term 1 Unit 3 Solution Guide PDF:

TN State Board Class 7th Science Subject Term 1 Unit 3 one mark and two mark solutions guide PDF available below.

Science – Term 1

Unit 3 Matter Around Us

I. Choose the appropriate answer :

1. Which of the following is an example of a metal?
(a) Iron
(b) Oxygen
(c) Helium
(d) Water
Answer:
(a) Iron

2. Oxygen, hydrogen, and sulphur are examples of which of the following?
(a) Metals
(b) Non-metals
(c) Metalloids
(d) Inert gases
Answer:
(b) Non-metals

3. Which of the following is a short and scientific way of representing one molecule of an element or compound?
(a) Mathematical formula
(b) Chemical formula
(c) Mathematical symbol
(d) Chemical symbol
Answer:
(d) Chemical symbol

4. The metals which is a liquid at room temperature
(a) Chlorine
(b) Sulphur
(c) Mercury
(d) Silver
Answer:
(c) Mercury

5. An element which is always lustrous, malleable and ductile
(a) non-metal
(b) metal
(c) Metalloid
(d) gas
Answer:
(b) metal

II. Fill in the blanks :

1. The smallest particle of matter that can exist by itself ______
2. A compound containing one atom of carbon and two atoms of oxygen is ______
3. ______ is the only non-metal conducts electricity.
4. Elements are made up of ______ kinds of atoms.
5. ______of some elements are derived from Latin or Greek names of the elements.
6. There are ______ number of known elements.
7. Elements are the ______ form of pure substances.
8. The first letter of an element always written in ______ letter.
9. Molecule containing more than three atoms are known as ______
10. ______ is the most abundant gas in the atmosphere.

Answer:

1. atom
2. CO₂
3. Graphite
4. same
5. Symbol
6. 118
7. simplest
8. capital
9. polyatomic molecule
10. Nitrogen

III. Analogy:

1. Mercury: liquid at room temperature:: Oxygen: _________
2. Non metal conducting electricity: _______ :: Metal conducting electricity: Copper
3. Elements: combine to form compounds:: Compounds: ________
4. Atoms: fundamental particle of an element:: ________ fundamental particles of a compound

Answer:

1. Gas at room temperature
2. Graphite
3. can be split into elements
4. elements

IV. State True of False. If False, give the correct statement.

1. Two different elements may have similar atoms.
Answer:
True

2. Compounds and elements are pure substances.
Answer:
True

3. Atoms cannot exist alone; they can only exist as groups called molecules.
Answer:
True

4. NaCl represents one molecule of sodium chloride.
Answer:
True

5. Argon is monoatomic gas.
Answer:
True

V. Answer in brief.

1. Write the chemical formula and name the elements present in the following compounds:
a. Sodium chloride
b. Potassium hydroxide
c. Carbon-di-oxide
d. Calcium oxide
e. Sulphur dioxide
Answer:

		Chemical formula	Elements present
a.	Sodium chloride	NaCl	Sodium (Na), Chlorine (Cl)
b.	Potassium hydroxide	KOH	Potassium (K), Oxygen (O), Hydrogen (H)
c.	Carbon-di-oxide	CO2	Carbon (C), Oxygen (O2)
d.	Calcium oxide	CaO	Calcium (C), Oxygen (O2)
e.	Sulphur dioxide	SO2	Sulphur (S), Oxygen (O2)

2. Classify the following molecules as the molecules of element or compound.

Answer:

3. What do you understand by chemical formula of a compound? What is its significance?
Answer:

1. A chemical formula is a symbolic representation of one molecule of an element or a compound.
2. It provides information about the elements present in the molecule and the number of atoms of each element. The chemical formula tells us the types of atoms and the number of each type of atom in one molecule of substance.

4. Define the following terms with an example of each:
a. Element
b. Compound
c. Metal
d. Non-metal
e. Metalloid
Answer:
(a) Element: It is a substance that cannot be broken down into simpler substance by chemical means Ex. : Oxygen, Hydrogen, Gold & Helium.

(b) Compound A compound is a pure substance that is formed when the atoms of two or more elements combine chemically in definite proportions. Ex: H?0, NaCl.

(c) Metal A chemical element that is an effective conductor of electricity and heat can be defined as a metal. Ex.: Copper, Iron, Silver, etc.

(d) Non-Metal Non-metal is an element that doesn’t have the characteristics of metal including, (i.e.) ability to conduct heat or electricity luster or flexibility. Ex. Carbon Iodine, Sulphur.

(e) Metalloid: Metalloid is a chemical element that exhibits some properties of metals and some of non-metals. Metalloids are generally semiconductors. Ex. : Silicon. Arsenic, Antimony, and Boron.

5. Write the symbols for the following elements and classify them as solid, liquid, and gas.
Aluminum, carbon, chlorine, mercury, hydrogen, and helium.
Answer:

Element	Symbol	Classification
Aluminum	Al	Solid
Carbon	C	Solid
Chlorine.	Cl	Gas
Mercury.	Hg	Liquid
Hydrogen.	H	Gas
Helium	He	Gas

6. Classify the following as metals, non-metals and metalloids
Sodium, Bismuth, Silver, Nitrogen, Silicon, carbon, chlorine, Iron, copper.
Answer:

Metal	Non-metal	Metal	Non-metal
Sodium	Metal	Carbon	Non-metal
Bismuth	Metal	Chlorine	Non-metal
Silver	Metal	Iron	Metal
Nitrogen	Non-metal	Copper	Metal
Silicon	Metalloid

7. Classify the following as elements and compounds.
Water, common salt, sugar, carbon dioxide, iodine and lithium
Answer:

Elements	Compounds
Water	Compound
Common salt	compound
Sugar	Compound
Carbon dioxide	Compound
Iodine	Element
Lithium	Element

8. Write the chemical formula for the following elements.
a. Hydrogen
b. Nitrogen
c. Ozone
d. Sulphur
Answer:

Elements	Formula
Hydrogen	H
Nitrogen	N
Ozone	O3
Sulphur	S

9. What are elements? What are they made of? Give two examples.
Answer:

1. Elements are chemically the simplest substances and hence cannot be broken down using chemical reactions.
2. It is made entirely from one type of atom.
3. Example: Hydrogen, Oxygen is made from atoms containing a single proton and a single electron.

10. Define molecule.
Answer:

1. When an atom combines with another atom (or atoms) and forms a compound it is called a molecule.
2. A molecule is made up of two or more atoms chemically combined.

11. What are compounds? Give two examples.
Answer:
A compound is a pure substance that is formed when the atoms of two or more elements combine chemically in definite proportions.
Example : H₂O, NaCl,

12. Give an example of the elements derived from their Latin names.
Answer:

Element	Latin Name	Symbol
Copper	Cuprum	Cu
Lead	Plumbum	Pb
Potassium	Kalium	K
Iron	Ferrum	Fe
Mercury	Hydrargyrum	Hg
Sodium	Natrium	Na

13. What is the atomicity of elements?
Answer:
Atomicity is the total number of atoms present in one molecule of an element, compound, or substance.

14. Calculate the atomicity of H2S04.
Answer:
A molecule of sulphuric acid (H₂S0₄) consists of 2 hydrogen atoms, 1 Sulphur atom, and 4 oxygen atoms. Hence its atomicity 2 + 1 + 4 = 7.

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