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Class VII Science T1U3 Matter around us Textbook Solutions
Matter Around Us
Evaluation
I. Choose the appropriate answer.
1. Which one of the following is an example for a metal?
a. Iron
b. Oxygen
c. Helium
d. Water
Ans: a. Iron
2. Oxygen, hydrogen, and sulphur are examples for
a. metals
b. non-metals
c. metalloids
d. inert gases
Ans: 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
Ans: b. Chemical formula
4. The metal which is liquid at room temperature is
a. chlorine
b. sulphur
c. mercury
d. Silver
Ans: c. mercury
5. An element which is always lustrous, malleable and ductile is
a. non-metal
b. metal
c. metalloid
d. Gas
Ans: b. metal
II. Fill in the blanks.
1. The smallest particle of matter that can exist by itself is ____________ .
Ans: atom
2. A compound containing one atom of carbon and two atoms of oxygen is ____________ .
Ans: Carbon di oxide
3. ___________is the only non-metal which conducts electricity.
Ans: Graphite
4. Elements are made up of _________ kinds of atoms.
Ans: same
5. ____________ of some elements are derived from Latin or Greek names of the elements.
Ans: Symbols
6. There are ____________ number of known elements.
Ans: 118
7. Elements are the ____________ form of pure substances.
Ans: simplest
8. The first letter of an element is always written in ____________letter.
Ans: Capital
9. Molecules containing more than three atoms are known as ____________.
Ans: polyatomic molecules
10. ____________ is the most abundant gas in the atmosphere.
Ans: Nitrogen
III. Analogy.
1. Mercury : Liquid at room temperature :: Oxygen: gas at room temperature.
2. Non-metal conducting electricity : Graphite :: Metal conducting electricity : Copper
3. Elements : Combine to form compounds :: Compounds : Combine to form mixtures.
4. Atoms : Fundamental particles of an element :: Molecules : Fundamental particles of a compound.
IV. State true of false. If false, give the correct statement.
1. Two different elements may have similar atoms.
False.
Atoms only make one element different from another.
2. Compounds and elements are pure substances.
True
3. Atoms cannot exist alone. They can only exist as groups called molecules.
True
4. NaCl represents one molecule of sodium chloride.
True
5. Argon is monoatomic gas.
True
V. Answer in brief.
1. Write the chemical formula and name the elements present in the following compounds.
2. Classify the following molecules as the molecules of element or compound.
Ans:
1. O2 - Oxygen -Molecule
2. CO2 - Carbon dioxide -Compound
3. N2 - Nitrogen -Molecule
4. NaCl - Sodium Chloride -Compound
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 for each.
a. Element
Matter in its simplest form is called an element and it can not be broken down further.
Example: Oxygen, Hydrogen etc
b. Compound
A compound is a pure substance that is formed when the atoms of two or more elements combine chemically in definite proportions.
Example: Water, Sodium Chloride
c. Metal
Elements that are typically hard, malleable,ductile and good conductors of heat and electricity are called metals.
Example: Copper, Iron, Gold etc.
d. Non-metal
A nonmetal is an element that is generally a poor conductor of heat and electricity and looks dull and soft.
Example: Carbon, Phosphorus etc.
e. Metalloid
The elements which exhibit the properties of both metals and nonmetals are called metalloids.
Example: Silicon, Arsenic etc
5. Write the symbols for the following elements and classify them as solid, liquid and gas.
6. Classify the following as metals, non-metals and metalloids.
7. Classify the following as elements and compounds.
8. Write the chemical formula for the following elements.
9. What are elements? What are they made of? Give two examples.
Matter in its simplest form is called an element and it can not be broken down further.
Example: Oxygen, Hydrogen etc
10. Define molecules.
A molecule is made up of two or more atoms chemically combined.
11. What are compounds? Give two examples.
Molecules of a compound consist of a fixed number of different types of atoms chemically combined.
12. Give an example for the elements derived from their Latin names.
13. What is atomicity of elements?
Atomicity implies the total number of atoms present in one molecule of an element, compound or a substance.
14. Calculate the atomicity of H2SO4.
Sulphuric acid - H2SO4
Sulphuric acid contains = 2 Hydrogen atom
= 1 Sulphur atom
= 4 Oxygen atom
--------
Total = 7
--------
So, the atomicity of H2SO4 - Sulphuric acid is 7.
VI. Answer in detail.
1. Differentiate metals and non-metals.
2. Explain the characteristics of compounds
A compound is formed only when the constituent elements combine in a fixed
proportion.
The properties of a compound are different from those of its constituent elements.
A compound cannot be broken down by physical methods. This is because a compound is made up of different elements
that are chemically combined. Sodium chloride cannot be separated by physical
methods such as filtration.
A compound can be separated into its constituent elements by chemical methods
only.
3. Describe the different ways in which we can write the symbols of elements. Give
appropriate examples.
The symbols of most elements start with the first letter of their English in Capitals. Ex. Boron- B, Carbon - C
When there is more than one element that starts with the same letter, alongwith the first letter their second letter is also taken to write the symbol.
Ex. Bismuth Bi, Calcium - Ca
First letter of the symbol is always in Capitals and the second letter of the symbol is always in small letters.
When the first two letters of the two elements start with the same letters, then the First letter of the element and third letter of the element is used to write symbols.
Ex. Argon- Ar, Arsenic- As
Some elements' symbols are the first letter of their Greek or Latin name.
Ex. Sodium- Natrium - Na
Iron - Ferrum -Fe
4. Differentiate between elements and compounds.
5. Write any five characteristics of compounds.
This question is repeated. Answer is the same as given in question number 2.
6. Compare the properties of metals and nonmetals. Give three examples for each.
This question is repeated. Answer is the same as given in question number 1.
7. Write down the properties of metalloids.
Metalloids exhibit the properties of both metals and nonmetals.
An appearance of metalloids are similar to metals
Metalloids are less conductive than metal
Metalloids are more brittle than metals
In general metalloids have nonmetallic chemical properties.
Ex.Silicon, arsenic, antimony, and boron are some examples of metalloids.
VII. Rewrite the given sentence in correct form.
1. Elements contain two or more kinds of atoms and compounds contain only one kind of atom.
Compounds contain two or more kinds of atoms and elements contain only one kind of atom.
VIII. Higher Order Thinking Skills.
1. List out the metals, non-metals and metalloids which you use in your house, schools. Compare their properties.
2. What changes take place in the movement and arrangement of particles during
heating process?
When a matter is heated,
Movement of the particle inside the matter increase
Internal energy increase and the volume of matter also increases
During heating the matter begins to expand and the distance between the particles increases.
During heating and expansion, the size of the particle remains the same size.
3. In the diagram given below, the circle, square and triangle represent the atoms of
different elements.
Identify all combinations that represent
a. molecule of a compound
b. molecule of an element consisting of two atoms
c. molecule of an element consisting of three atoms
a.
b.
c.
4. Aakash noticed that the metal latch on gate was difficult to open during hot sunny days. However, it was not difficult to open the same latch at night. Aakash observed that the latch and the gate are exposed to the sun during day time.
a. Formulate a hypothesis based on the information provided.
b. Briefly state how you would test the hypothesis.
As the metal tends to expand on heating, during sunny days, the metal latch on the gate was difficult to open.
In general, the temperature decreases at night, so the metal latch contrats and there is no difficulty in opening the latch.
Practically it can be tested with a small iron bolt and nut. Heat the bolt alone for sometime and try to screw the nut with the help of gloves. It may not be possible to do; but after cooling, the bolt and nut may be screwed easily. This proves that metal expands on heating and contracts on cooling.
IX Consider the following statements and choose the correct option.
a. Both assertion and reason are true and reason is the correct explanation of assertion.
b. Both assertion and reason are true, but reason is not the correct explanation of assertion.
c. Assertion is true but reason is false.
d. Assertion is false but reason is true.
1. Assertion: Oxygen is a compound.
Reason: Oxygen cannot be broken down into anything simpler.
2. Assertion: Hydrogen is an element.
Reason: Hydrogen cannot be broken down into anything simpler.
3. Assertion: Air is a compound.
Reason: Air consists of carbon dioxide.
4. Assertion: Air is a mixture of elements only.
Reason: Only nitrogen, oxygen and neon gases exist in air.
5. Assertion: Mercury is solid in room temperature.
Reason: Mercury is a non-metal.
Answers:
d. Assertion is false but reason is true.
b. Both assertion and reason are true, but reason is not the correct explanation of assertion.
d. Assertion is false but reason is true.
Both the statements are false.
Both the statements are false.
