Nik Syllabus

Carbon and its compounds, Periodic Classification of Elements, How do Organisms Reproduce, Heredity & Evolution, Electricity, Magnetic Effect of current, Our Environment, Management of Natural Resources.

Periodic Table - 

1. As we move along a period (means Left to Right), size decreases as electrons are being added in the same shell and with increase in atomic no. effective nuclear charge increases, hence electrons are held tightly by the nucleus.

2. As we move down the group, size increases as electrons are being added in the new shells and due to shielding effect effective nuclear charge decreases hence electrons are loosely held by the nucleus.

Valence electrons - Total no. of electrons in the outermost shell

Valency - No. of electrons lost or gain to attain noble gas configuration.

+ve means electron donation

-ve means electron gain.

Q1 How could the Modern Periodic Table remove various anomalies of Mendeléev’s Periodic Table? 

Ans. Modern Periodic Table is based on arrangement of elements on their atomic No. However, Mendeleev's Periodic Table is based on the arrangement of elements on their atomic mass. 

Q2 Name two elements you would expect to show chemical reactions similar to magnesium. What is the basis for your choice? 

Ans. Two elements show chemical reactions similar to magnesium are: Be, Ca.

Be and Ca both belong to Gp 2 and both have two electrons in their outermost shell like Mg.

Q3 Name 

(a) three elements that have a single electron in their outermost shells. - Li, Na, K, Rb, Cs, Fr

(b) two elements that have two electrons in their outermost shells - Be, Mg, Ca, Sr, Ba, Ra

(c) three elements with filled outermost shells - He, Ne, Ar, Kr, Xe, Rn.

Q4 (a) Lithium, sodium, potassium are all metals that react with water to liberate hydrogen gas. Is there any similarity in the atoms of these elements? 

Ans. These belong to Gp 1 family and they have only one electron in their outermost shell and hence these are strong metals.  They react with water to liberate hydrogen gas.

(b) Helium is an unreactive gas and neon is a gas of extremely low reactivity. What, if anything, do their atoms have in common?

Ans. Both He and Ne belong to Gp 18 family. They have fully filled outermost shell. They neither gain or lose electrons. They are inert. They are commonly known as noble gases.

5. In the Modern Periodic Table, which are the metals among the first ten elements? 

Ans. Li, Be.

6. By considering their position in the Periodic Table, which one of the following elements would you expect to have maximum metallic characteristic? 

Ga Ge As Se Be 

Ans. Ga.

Metallic character decreases left to right and increases down the group.

Be and Ga are metallic in nature. Ga is bigger in size and hence has more tendency to lose electrons.

Intext Questions: 

1. Use Mendeléev’s Periodic Table to predict the formulae for the oxides of the following elements: K, C, AI, Si, Ba. 

Ans.K2O, CO2, Al2O3 , SiO2, BaO.

2. Besides gallium, which other elements have since been discovered that were left by Mendeléev in his Periodic Table? (any two)

Ans. Germanium and Scandium

3. What were the criteria used by Mendeléev in creating his Periodic Table? 

Ans. The criteria used by Mendeleev in creating his periodic table were: 

(i) The atomic mass of the elements was used to arrange the elements. 

(ii) Grouping the elements according to their similar chemical properties.

4. Why do you think the noble gases are placed in a separate group?

Ans. Due to following reasons: 

a. full filled outermost shell

b. They are inert and do not react

1. Did Döbereiner’s triads also exist in the columns of Newlands’ Octaves? Compare and find out.

Ans. Yes, Dobereiner's triads also exist in the columns of Newlands Octaves. For example, the second column of Newlands classification has the elements lithium (Li), sodium (Na) and Potassium (K), which constitute a Dobereiner's triad.

2. What were the limitations of Döbereiner’s classification?

Ans.  Dobereiner could find only three triads; . i.e total of 9 elements only. The law was not holding good for elements having very high mass or very low mass. Not all groups obeyed the Law of Triads.

3. What were the limitations of Newlands’ Law of Octaves?

Ans. The major limitations of Newlands' law of octaves were : 

(i) It was applicable to only lighter elements having atomic masses upto 40 u, i.e., upto calcium

(ii) It was assumed that only 63 elements existed in nature and no new elements would be discovered in the future.

Q4 Calculate Valency and Valence electrons of Gp 17.

Ans. F, Cl, Br, I belong to Gp 17 family. They have seven electrons in their outermost. Their Valency is 1. Their Valence electrons are 7.

Carbon & Its Compounds

- Every elements wants to attain noble gas electronic configuration and they do it by either losing or gaining electrons.

- Metals lose electrons and attain configuration of the nearest noble gas. Like Li loses one electron and attains configuration of Noble Gas He.

- Non metals gain electrons and attain configuration of the nearest noble gas. Like F gains one electron and attain configuration of noble gas Ne.

- However elements in the mid of the periodic table make covalent bonds to satisfy themselves to reach noble gas configuration.

- Covalent Bond: - When a bond is formed by two atoms by sharing one electron by each.

- Carbon has four electrons in its outermost shell. Its valency and valence electrons both are four. It cannot gain or lose four electrons in total due to following reasons: 

a. it could gain four electrons forming C4- anion. But it would be difficult for the nucleus with six protons to hold on to ten electrons, that is four extra electrons.

b. it could lose four electrons forming C4+ cation. But it would require a large amount of energy to remove four electrons leaving behind a carbon cation with six protons in its nucleus on to just two electrons.

- Carbon forms four covalent bonds.