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class VIII

Key Concepts

atoms, molecules, electrons, protons, cations, anions, cathode, anode, isotopes, valency

essential questions

1. What is an element?
2. What is an atom?
3. What happens to an atom when its structure is changed?
4. How do knowledge and understanding of elements impact different aspects of our lives?


  1. What are isotopes? Give example.
  2. What are Electrovalent compounds? Give example
  3. What are the essential conditions required to form electrovalent compounds? Show with examples
  4. What are covalent compounds?
  5. Which one of the following contains ionic, covalent and coordinate bonds? a) NaOH  b) NaCl  c) NaCN  d) NaNC
  6. How many different types of atom are in an NH3 molecule?
  7. In a dot and cross diagram, what does each dot represent?
  8. What is the greatest number of covalent bonds that one carbon atom can form?
  9. Read the following statements and mark True or false:

a) Silver objects become green and lose their shine with passage of time

b) Silver reacts with carbon dioxide and moisture present in the atmosphere



  1. What is Dalton’s Atomic Theory?
  2. Describe the cathode and anode ray experiment and their significance.
  3. How did Chadwick prove that neutron have mass too but no charge?
  4. Looking at the formulas of Atomic mass and atomic number, can you tell the difference between the two. Give with examples
  5. Explain in detail the uses and harmful effects of Radioactivity
  6. Explain the difference between Cations and Anions by using example of K and Cl.


  1. As per the electronic configuration, an element has 2 electrons in K and 5 electrons in L shell. What can you tell about this element by looking at the electronic configuration?
  2. The oxide of sulphur (which can be further oxidised) when dissolved in water gives : a) H2S b) H2SO4 c) H2SO4     d) H2


  1. An unknown metal X when place in copper sulphate solution, red brown pieces of copper fall to the bottom of the test tube. When metal X is placed in aluminium sulphate solution, no change is observed. What is metal X?
  2. Substances X reacts with dilute HCL violently, Y reacts slowly while Z does not react all. X, Y, Z could be respectively: a)Cu, Al.Fe     b) Al, Na, Cu    c) Na, Cu, Fe   d) K, Al, Cu
  3. Read the following statements carefully and identify X, Y and Z respectively. a) X is stored under kerosene b) Y catches fire on exposure to air and stored water  c) Z reacts with steam  Choose the correct option: a) Na, Mg, Cu b) Na, P, Fe c) Cu, Zn, K       d) Zn, Cu, Na