Samacheer Kalvi 7th Science Term 1 Unit 3 Book Back Question and Answers/Solutions:
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Samacheer Kalvi 7th Science Book Back Chapter 3 Term 1 Answers/Solutions Guide PDF:
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7th Science – Term 1 Chapter 3
Matter Around Us
I. Choose the appropriate answer:
1. Which of the following is an example of a metal?
2. Oxygen, hydrogen, and sulphur are examples of which of the following?
(d) Inert gases
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
(d) Chemical symbol
4. The metals which is a liquid at room temperature
5. An element which is always lustrous, malleable and ductile
II. Fill in the blanks :
- The smallest particle of matter that can exist by itself ______
- A compound containing one atom of carbon and two atoms of oxygen is ______
- ______ is the only non-metal conducts electricity.
- Elements are made up of ______ kinds of atoms.
- ______of some elements are derived from Latin or Greek names of the elements.
- There are ______ number of known elements.
- Elements are the ______ form of pure substances.
- The first letter of an element always written in ______ letter.
- Molecule containing more than three atoms are known as ______
- ______ is the most abundant gas in the atmosphere.
- polyatomic molecule
- Mercury: liquid at room temperature:: Oxygen: _________
- Non metal conducting electricity: _______ :: Metal conducting electricity: Copper
- Elements: combine to form compounds:: Compounds: ________
- Atoms: fundamental particle of an element:: ________ fundamental particles of a compound
- Gas at room temperature
- can be split into elements
IV. State True of False. If False, give the correct statement.
1. Two different elements may have similar atoms.
2. Compounds and elements are pure substance.
3. Atoms cannot exist alone; they can only exist as groups called molecules.
4. NaCl represents one molecule of sodium chloride.
5. Argon is mono atomic gas.
V. Answer in brief.
1. Write the chemical formula and name the elements present in the following compounds:
a. Sodium chloride
b. Potassium hydroxide
d. Calcium oxide
e. Sulphur dioxide
|Chemical fromula||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)|
3. What do you understand by chemical formula of a compound? What is its significance?
- A chemical formula is a symbolic representation of one molecule of an element or a compound.
- 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: 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 semi-conductors. 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.
6. Classify the following as metals, non-metals and metalloids
Sodium, Bismuth, Silver, Nitrogen, Silicon, carbon, chlorine, Iron, copper.
7. Classify the following as elements and compounds.
Water, common salt, sugar, carbon dioxide, iodine and lithium
8. Write the chemical formula for the following elements.
9.What are elements? What are they made of. Give two examples.
- Elements are chemically the simplest substances and hence cannot be broken down using chemical reactions.
- It is made of entirely from one type of atom.
- Example : Hydrogen, Oxygen is made from atoms containing a single proton and a single electron.
10. Define molecule.
- When an atom combines with another atom (or atoms) and forms a compound it is called as molecule.
- A molecule is made up of two or more atoms chemically combined.
11.What are compounds? Give two examples.
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 for the elements derived from their Latin names.
13. What is atomicity of elements?
Atomicity is the total number of atoms present in one molecule of an element, compound or a substance.
14. Calculate the atomicity of H2S04.
A molecule of sulphuric acid (H2S04) consists of 2 hydrogen atom, 1 Sulphur atom and 4 oxygen atoms. Hence its atomicity
2 + 1 + 4 =7.
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