Structure of the Atom — Science STD 9 — Question

There are three substances X, Y and Z. The substance X does not have a fixed melting point or boiling point and it still shows the individual properties of its constituents. The substance Y is a pure substance which occurs in nature as such. The substance Y has a fixed melting point and boiling point but it cannot be broken down into simpler substances by any chemical means. The substance Z is also a pure substance whose properties are entirely different from those of its constituents. The substance Z can, however, be divided by electrolysis into two substances which belong to the same class of substances as Y.

1. What type of substance could X be? Name one substance like X.
2. What type of substance could Y be? Name one substance like Y.
3. What type of substance could Z be? Name one substance like Z.
4. Whish process involves absorption or release of an appreciable amount of energy: formation of substance X or formation of substance Z?
5. Name the three groups into which all the substances like Y are divided on the basis of their properties.

When extremely small particles X derived from the another of a flower were suspended in a liquid Y and observed through a microscope, it was found that the particles X were moving throughout the liquid Y in a very zig zag way. It was also observed that warmer the liquid Y, faster the particles X moved in its surface.

1. What could particles X be?
2. What do you think liquid Y is?
3. What is the zig-zag movement of particles X?
4. What is causing the zig-zag movement of particles X?
5. Name the scientist who discovered this phenomenon.
6. What does this experiment tell us about the nature of liquid Y?

Classify the following as chemical or physical changes:

• Cutting of trees.
• Melting of butter in a pan.
• Rusting of almirah.
• Boiling of water to form steam.
• Passing of electric current, through water and the water breaking down into hydrogen and oxygen gases.
• Dissolving common salt in water.
• Making a fruit salad with raw fruits.
• Burning of paper and wood.

In this crossword puzzle (Figure), names of 11 elements are hidden. Symbols of these are given below. Complete the puzzle.

1. Cl
2. H
3. Ar
4. O
5. Xe
6. N
7. He
8. F
9. Kr
10. Rn
11. Ne

There is a large group of materials P which can be divided into three groups Q, R, and S on the basis of their properties. The substances belonging to group Q can be solids, liquids or gases. The solids belonging to group Q are usually electrical insulators. Most of the substances of group R are solids which are good conductors of electricity. The substances belonging to group S are neither insulators like Q nor good conductors like R. The properties of S are intermediate between those of Q and R.

1. What could the group of materials P be?
2. Name the substances Q. Give two examples of such substances.
3. Name the substances R. Write two examples of such substances.
4. Name the substances S. Give two examples of such substances.
5. Out of Q, R and S, which substances are malleable and ductile?

Describe the process to show that the dye used in blue/black ink is a mixture of two or more components with diagram.

Give the main differences between physical changes and chemical changes.

The atom of an element X has 7 electrons in its M shell:

1. Write the electronic configuration of element X.
2. What is the atomic number of element X?
3. Is it a metal or a non-metal?
4. What type of ion will be formed by an atom of element X? Write the symbol of the ion formed.
5. What could element X be?

State the law of constant proportions. Give one example to illustrate this law.

What weight of oxygen gas will contain the same number of molecules as 56g of nitrogen gas?
(O = 16u; N = 14u)