The comprehensive approach in SCERT Class 8 Basic Science Textbook Solutions Chapter 5 Elements and Compounds Important Questions ensure conceptual clarity.
Elements and Compounds Extra Questions and Answers Class 8 Basic Science Chapter 5 Kerala Syllabus
Elements and Compounds Class 8 Important Questions
Question 1.
All matter is made up of minute particles called _____________ .
a) Atom
b) Molecule
c) Element
d) Compound
Answer:
a) Atom
Question 2.
____________ discovered that water could be split into hydrogen and oxygen by passing electricity through it.
a) Mendeleev
b) Henry Moseley
c) Cavendish
d) Humphry Davy
Answer:
d) Humphry Davy
Question 3.
Cr is the symbol for which element?
a) Calcium
b) Chromium
c) Chlorine
d) Carbon
Answer:
b) Chromium
Question 4.
Who invented the modern periodic table?
Answer:
Henry Moseley
Question 5.
An ammonia molecule contains one nitrogen atom and three hydrogen atoms. How would you represent five ammonia molecules?
Answer:
5NH3
Question 6.
Find the relation and fill up the blanks.
Sodium – (Na): Natrium – Latin name
Potassium – (K): ______________ .
Answer:
Kalium – Latin name
Question 7.
Find the monoatomic element from the following.
a) Hydrogen
b) Helium
c) Oxygen
d) Chlorine
Answer:
b) Helium
Question 8.
Find the Odd one out.
a) Rutherfordium
b) Nobelium
c) Rubidium
d) Einsteinium
Answer:
Rubidium (Others are synthetic elements)
Question 9.
Which group is not included in Dobereiner’s triads?
a)
| Li, Na, k |
b)
| He, Ne, Ar |
c)
| Ca, sr, Ba |
d)
| CI, Br, I |
Answer:
b)
| He, Ne, Ar |
Question 10.
Give an example of a polyatomic element.
Answer:
Phosphorous (P4)
Sulphur (S8)
Question 11.
a) What is the white powder formed when magnesium burns in air?
b) Write its chemical formula.
Answer:
a) Magnesium Oxide
b) MgO
Question 12.
a) Which substances are obtained when sugar is heated strongly in a dry boiling tube?
b) Which of these is an element? Which is a compound?
Answer:
a) Carbon – water
b) Element – Carbon
Compound – Water
Question 13.
What is the basis for naming the elements given below?
a) Mendelevium
b) Rubidium
Answer:
a) From the name of the scientist Mendeleev
b) From the basis of red colour
Question 14.
Write the names of two elements that are found in liquid state at normal temperature.
Answer:
Mercury, Bromine
Question 15.
How do elements and compounds differ?
Answer:
Elements are pure substances made up of the same type of atoms. They cannot be further divided into components through chemical reactions.
Compounds are pure substances formed by the combination of atoms of two or more elements in a fixed ratio. These can be dissociated into constituent elements through chemical reactions.
Question 16.
The symbol for the element hydrogen is H. What is the difference between 2H and H2?
Answer:
2H refers the two atoms of Hydrogen.
H2 refers to a nitrogen molecule formed by two atoms.
Question 17.
Find the number of molecules and the total number of atoms in the following.
a) O2
b) 5F2
Answer:
a) No. of molecules – 1
Total no. of atoms – 2
b) No. of molecules – 5
Total no. of atoms – 10
Question 18.
It is said that oxygen is an element and carbon dioxide is a compound. Why?
Answer:
In an oxygen molecule, there are only the same type of atoms.
In carbon dioxide, there is the combination of atoms of the elements oxygen and carbon in a fixed ratio.
Question 19.
a) What are the components of water?
b) How can we separate the components of water?
Answer:
a) Hydrogen, Oxygen
b) Water can be split into its components by passing electricity through it.
Question 20.
a) What are periods and groups in the periodic table?
b) How many of these are there in the modern periodic table?
Answer:
a) The horizontal rows in the table are called periods and the vertical columns are called groups. Elements in a group show similar chemical properties.
b) Periods – 7
Groups – 18
Question 21.
When the element carbon burns in air, it combines with oxygen to form carbon dioxide gas.
a) Write what are the reactants and products in this reaction.
b) Write the chemical equation for this reaction using symbols and chemical formulas.
Answer:
a) Reactants: – Carbon (C)
Oxygen (O2)
Products – Carbon dioxide (CO2)
b) C + O2 → CO2
Question 22.
Classify the following into elements and compounds and list them.
• Carbon
• Carbon dioxide
• Ammonia
• Sodium chloride
• Oxygen
• Sodium
Answer:
| Elements | Compounds |
| • Carbon • Oxygen • Sodium |
• Carbon dioxide • Ammonia • Sodium Chloride |
Question 23.
Write any three ideas in John Dalton’s atomic theory.
Answer:
- All matter is made up of minute particles called atoms.
- An atom is the smallest particle that can participate in a chemical reaction.
- An atom cannot be divided during a chemical reaction.
- An atom cannot be created or destroyed.
- All atoms of an element are of the same size, property and mass.
- Atoms of different elements differ in their size, property and mass, (any three)
Question 24.
The molecular formula of a compound is H2SO4.
a) What elements are contained in this compound?
b) Find the total number of molecules contained in 5H2SO4 and also the total number of atoms.
Answer:
a) Hydrogen (H)
Sulphur (S)
Oxygen (O)
b) Number of molecules = 5
Total number of atoms = 35
(H = 10, S = 5, O = 20)
Question 25.
What are the advantages of the periodic table prepared by Mendeleev?
Answer:
- Mendeleev arranged the 63 elements known till that day in ascending order of their atomic masses and prepared a table.
- Blank spaces were left for elements to be discovered and their properties were predicted.
- Elements with similar properties were grouped together to simplify the study of elements and their compounds.
Question 26.
What are the limitations of Mendeleev’s periodic table?
Answer:
- The order of atomic mass was not strictly followed in the case of all elements. Hydrogen could not be given an exact position.
- Elements with very different properties had to be placed in the same group.
Question 27.
The names of some scientists and their contributions are given in the table. Write them in the correct order.
| A | B |
| Splitting of water by passing electricity through it | Henry Moseley |
| Representation of elements by letters | Sir Humphry Davy |
| Modern Periodic table | Berzelius |
Answer:
| A | B |
| Splitting of water by passing electricity through it | Sir Humphry Davy |
| Representation of elements by letters | Berzelius |
| Modern Periodic table | Henry Moseley |
Question 28.
Sugar is heated strongly in a dry boiling tube.
a) What will be the observation?
b) What products are formed?
c) What are the elements in sugar?
Answer:
a) Observation – A black substance remains in the boiling tube.
b) Carbon (C), Water (H2O)
c) Carbon (C), Hydrogen (H), Oxygen(O)
Question 29.
Below are some statements related to early attempts at element classification. Match the statements with the ones in brackets that match them.
(Mendeleev, Dobereiner, Berzelius, Lavoisier, Newlands, Henry Moseley)
a) Classified the then-known elements into metals and non-metals.
b) Classified the elements of similar properties into groups of three.
c) Arranged the elements in ascending order of their atomic masses.
Answer:
a) Lavoisier
b) Dobereiner
c) Mendeleev
Question 30.
The names, nomenclature, and symbols of some elements are given in A, B, C columns. Match these in the correct order and write them.
| A Element |
B Nomenclature |
C Symbol |
| Chromium | From the Latin name | Cr |
| Copernicium | From the Greek word, which means colour | Cn |
| Copper | From the name of a scientist | Cu |
Answer:
| A Element |
B Nomenclature |
C Symbol |
| Chromium | From the Greek word, which means colour | Cr |
| Copernicium | From the name of a scientist | Cn |
| Copper | From the Latin name | Cu |