Periodic Table || Mendellev's periodic table || Modern Periodic Table

Q1. What is periodic table?

Ans:

The table which is obtained after the arrangement of elements according to their similarities and dissimilarities is called periodic table.

Q2. State Mandeleev's periodic law.

Ans:

It states that the physical and chemical properties of the elements are the periodic functions of their atomic masses.

Q3.What are meant by group and period?

Ans:

The horizontal row in a periodic table is called period and vertical column is called group.

Q4. What are the advantages of Mendeleev's periodic table?

Ans:

The following are the advantages of Mandeleev's periodic table;

1. It was the first systemic arrangement of elements in a table.
2. It is promoted the discovery of new elements by leaving the gaps.

Q5. List out the draw backs of Mandeleev's periodic table.

Ans:

The following are the some drawbacks of Mendeleev's periodic table;

1. The position of hydrogen is not properly explained.
2. Some chemically dissimilar elements have been placed in the same group.
3. Metals and non metals were not separated.

Q6. State modern periodic law.

Ans:

It states that the physical and chemical properties of elements are periodic function of their atomic number.

Q7. What are the advanatages of modern periodic table?

Ans:

The advantages of modern periodic table are;

• Hydrogen is kept in group I of periodic table.
• The wrong position of some elements like potassium and argon has been solved by arranging with respect to their atomic number.
• Metals and non-metals are separated.

Q8. Distinguish between Mendeleev's periodic table and Modern Periodic table.

Ans:

Mendeleev's Periodic Table	Modern Periodic Table
i) Elements are arranged in increasing order of their atomic mass.	i) Elements are arranged in increasing order of their atomic number.
ii) There were only 63 elements.	ii) There are about 118 elements.

Q9. The elements of group VIII are called inert or nobel gas, why?

Ans:

The outermost orbit of group VIII elements contain eight electrons. This means they are stable and do not take part in chemical reaction. So, they are called inert or noble gas.

Q10. Identify the group and period of following elements: Oxygen, Calcium, Lithium, Argon, Magnesium.

Ans:

Elements	Group	Period
Oxygen	VIA	2
Calcium	IIA	4
Lithium	IA	2
Argon	VIIIA	3
Magnesium	IIA	3

Q11. Give reason:

1. Neon is an inert gas.
Ans:
The outermost orbit of Neon contains eight elements. It does not lose, gain or share its valence electrons during chemical reaction. So, neon is an inert gas.
2. The valency of oxygen is two.
Ans:
Osygen atom tries to get two electrons during chemical change to be stable. So, its valency is two.
3. The elements of group IA are called alkali metals.
Ans:
The elements of group IA of modern periodic tbale are
4. CHlorine is claled reactive non-mental
Ans:
The outermost orbit of chlorine contains seven electrons and chlorine atom tries to get one electron to be stable. So, chlorine is called reactive non-metal.

Q12. Define chemical reaction. 

Ans:

The process in which one or more substances undergo change in molecular level to form a new substance is called chemical reaction.

Q13. What is mneant by word equation? Write with example. 

Ans:

The chemical reaction expressed in the name of chemical substance is called word equation. For example;

Hydrogen + Oxygen = Water

Potassium Chlorate = Potassium chloride + Oxygen

Q14. Define formula equation with example.

Ans:

The chemical equation expressed in terms of chemical formula or molecular formula is called formula equation. For example;

H₂ + O₂ = H₂O

Q15. What are reactants and products?

Ans:

The chemical substance which undergo chemical change to form a new substance are called reactants.

The new substances which are formed as a result of chemical change are called products.

Q16. Write any three differences between the physical and chemical change.

Ans:

Physical Change	Chemical Change
Physical change is a temporary change during which no new substance is formed.	Chemical change is a permanent change in which new substances are formed.
It is a temporary change.	It is a permanent change.
Change in energy is usually not seen. Example: Melting of ice.	Usually chnage is absorbed or evolved. Example: Burning of Magnesium ribbon.