Science [5 marks Questions]

1. The symbols of elements in increasing order of their atomic numbers are:

H, He, Li, Be, B, C, N, O, F, Ne, Na, Mg, Al, Si, P, S, Cl, Ar, K, Ca.

2. The symbols of elements in increasing order of their group numbers are as follows.

1. X is in Group 17, period 3 and Y is in group 2, period 4.
2. X is a non-metal, While Y is a metal.
3. Oxide of element Y would be basic. This compound is formed by ionic bond.
4.  

1. The available information suggests that the element X is nitrogen (N) and exists in diatomic form as N, Electronic configuration of N(Z = 7); 2, 5. It has five valence electrons.
2.  

3.  

The arrangement of given elements in the Modern Periodic table is listed below.

Group/ Period	1	2	13	14
3		Mg
4	K	Ca	Ga	Ge

We know that metallic character decreases from left to right in the periodic table. In the given elements, excluding Mg, remaining elements are placed in same period so the metallic character will decrease from K to Ge and order of metallic character would be;
Ge < Ga < Ca < KNow, as we move down in a group, metallic nature of elements increases. So, Ca is more metallic than Mg. Similarly, Mg will be less metallic than K because in period, metallic nature decreases from left to right. Hence the increasing order of metallic character would be;
Ge < Ga < Mg < Ca < K

1. Element with 3 as atomic number, i.e. Lithium.
2. Element with 9 as atomic number, i.e. Fluorine.
3. Fluorine.
4. Carbon, valency 4.

Inert gases could be placed in Mendeleev’s Periodic Table without disturbing the original order.
Noble gases; like Helium, Neon and Argon had been mentioned by various scientists even before Mendeleev. But these gases could be grouped together as noble gases much later than Mendeleev’s discovery. Mendeleev used 63 elements till his periodic table because these were the only known elements till his time. However, he was bold enough to leave gaps in his periodic table. He had predicted that that more elements would be discovered in times to come.
Mendeleev’s Periodic Table was the first comprehensive attempt to classify elements on the basis of their chemical properties. This is the main reason that new elements could be easily placed in Mendeleev’s Periodic Table without disturbing the original order.

1. Sodium (Group 1 and Period 3) or Potassium (Group 1 and Period 4).
2. Phosphorus (Group 15 and Period 3). It shows variable valencies 3 and 5 and is stored under water.
3. Carbon (Group 14 and Period 2).
4. Helium (Group 18 and Period 1).
5. Aluminium (Group 13 and Period 3).

Across:

1. Magnesium.

3. Tin.
4. Iodine.

Down:

2. Sodium.

5. Lithium.
6. Neon.
7. Astatine.
8. Iron.
9. Boron.

Mendeleev purposed the relation between atomic masses of elements and their properties. He examined that physical and chemical properties of elements are periodic function of their atomic masses. He arranged all known 63 elements according to their atomic masses.
He examined the compounds formed by elements hydrogen and oxygen. He used these elements because they readily form different compounds with other elements like hydride and oxides.
The chemical properties of hydrides and oxides were used to determine the chemical properties of different elements and that again used for their classification. He recorded properties of all 63 elements and paired the elements which exhibit same chemical properties. Later he arranged elements on the basis of their similarities in chemical properties and found that most of the elements were arranged in order of their increasing atomic masses.
In this arrangement, he also observed the periodic recurrence of elements with similar physical and chemical properties. He formulated the periodic law which states that the properties of elements are the periodic function of their atomic masses.