Science [5 marks Questions]

Merits of modern periodic table:

1. The modern periodic table is based on the atomic numbers of elements which is the most fundamental property of elements.
2. It helps us to understand why elements in a group show similar properties but elements in different groups show different properties.
3. It explains the reasons for the periodicity in properties of elements.
4. It tells us why the properties of elements are repeated after 2, 8, 18 and 32 elements.

1. No. This is because the elements Na, Si and Cl do not have similar properties even though the atomic mass of middle element Si is almost equal to the average atomic mass of first element Na and third element Cl.
2. Yes. This is because the elements Be, Mg and Ca have similar properties and the atomic mass of middle element Mg is almost equal to the average atomic mass of first element Be and third element Ca.

1. A (size decreases from left to right in a period).
2. K (valency of k = 3; valency of o = 1).
3. I (metallic character decreases from left to right in a period).
4. G (non - metallic character increases from left to right in a period).
5. B (or j).
6. F (or n).

1. Newlands' law of octaves is illustrated by the above arrangement of elements.
2. John Newlands is the scientist who proposed this classification of elements.
3. This classification is compared with a characteristic of the musical scale because the repetition of the properties of elements is just like the repetition of the eighth note in an octave of music.

4. Limitation:

Newlands' law of octaves could only be applied up to the element calcium.

1. On moving from left to right in a period, the chemical reactivity of elements first decreases and then increases.

Example: In the 3rd period of elements, sodium is a very reactive element, magnesium is less reactive whereas aluminium is still less reactive. Silicon is the least reactive in the third period. Now, phosphorus is quite reactive, sulphur is still more reactive whereas chlorine is very reactive.

2. On moving from left to right in a period, the basic nature of oxides decreases and the acidic nature of oxides increases.

Example: In the 3rd period of the periodic table, sodium oxide is highly basic in nature and magnesium oxide is comparatively less basic. The aluminium and silicon oxides are amphoteric in nature. Phosphorus oxides are acidic, sulphur oxides are more acidic whereas chlorine oxides are highly acidic in nature.

Advantages of the periodic table:

1. It has made the study of chemistry systematic and easy.
2. It is easier to remember the properties of an element if its position in the periodic table is known.
3. The type of compounds formed by an element can be predicted by knowing its position in the periodic table.
4. It is used as a teaching aid in chemistry in schools and colleges.

1. 2.

For groups 1 and 2, the number of valence electrons is equal to the group number.

2. 2.

Valency is determined by the number of valence electrons present in the atom of the element.

3. 5.

For groups 13 to 18, the number of valence electrons is equal to (group no. – 10).

4. 3.

The number of electrons lost or gained by one atom of an element to achieve the nearest inert gas configuration, gives us the valency.

1. d.
2. c.
3. e.
4. Covalent bond.
5. Ionic bond.

1. Neon (2, 8).
2. Magnesium.
3. Silicon (2, 8, 4).
4. Boron (2, 3).
5. Carbon (2, 4).