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1. s, p – block elements are called representative elements because these are the elements which take part in chemical reactions because of incompletely filled outermost shell. 

2. These elements undergo chemical reactions to acquire the nearest noble gas configuration by losing or gaining or sharing of electrons. 

3. So they are called representative elements.

1. Physical and chemical properties of elements are related to their electronic configurations, particularly the outer shell configurations. 

2. Therefore, all the elements in a group should have similar chemical properties. 

3. Similarly, across the table from left to right in any period, elements get an increase in the atomic number by one unit between any two successive elements. 

4. Therefore, the electronic configuration of valence shell of any two elements in a period is not same. Due to this reason, elements along a period possess different chemical properties.

i) Y belongs to second period.

ii) Z belongs to second group,

iii) X belongs to 18th group.

1. 1s² 2s² 2p⁶ 3s² 3p 

2. 3 

3. VII A or 17 

4. Halogen family 

5. 7 

6. 1 

7. Non-metal

A karate player can break a pile of tiles with a single blow of his hand because the force exerted by him is large enough to break these tiles as the momentum of his land is reduced to zero.

According to electronic configuration A = Be B = Mg C = P D = Ne

1.  A and D i.e. Be and Ne coming within the same period. [They have same valence shell (n = 2)]

2. A and B i.e., Be and Mg coming within the same group. [They have same valence subshell with same valency (2s² and 3s²)]

3. D, i.e. Ne is the noble gas element. [It has valency as ‘O’ and it has ‘8’ electrons in valence shell].

4. Element ‘C’ i.e. ‘P’ belongs to 3 period and VA group.

Mass of the toy car, m = 200g = 0.2kg 

Speed, v = 5 m/s

Momentum, p = mv = 1kg.m/s

The quantity is electronic configuration. 

1. Modern periodic table is based on electronic configuration. So elements are arranged in ascending order of their atomic numbers. 

2. The chemical properties of elements depend on valence electrons. The elements in same group have same number of valence electrons. So the elements belonging to same group have similar properties. 

3. So the construction of modern periodic table mainly depends on electronic configuration. 

4. Thus electronic configuration plays a major role in the preparation of modern periodic table. So its role is thoroughly appreciated.

1) Depending upon which sub-shell the differentiating electron enters, the elements are classified into s, p, d and f-block elements. They are 

1. s – block elements, 

2. p – block elements,

3. d – block elements, 

4. f – block elements.

2) s – block elements : 

i) If the differentiating electron enters in s-subshell, then the elements are called s-block elements. 

ii) IA (1), IIA (2) group elements belong to this block. 

3) p – block elements : 

i) If the differentiating electron enters in p-subshell, then the elements are called p-block elements. 

ii) IIIA(13), IV A (14), V A (15), VIA (16), VIIA (17) belong to p-block. 

4) d – block elements : 

i) If the differentiating electron enters in d-subshell, then the elements are called d – block elements. 

ii) I B, II B, III B, IV B, V B, VI B, VII B, VIII B belong to d-block elements. 

iii) They are also called transition elements. 

5) f – block elements : 

i) If the differentiating electrons enter in f-subshell, then the elements are called f-block elements. 

ii) These are divided into two types a) Lanthanides (41 elements), b) Actinides (5f elements). 

iii) These are also called as inner transition elements. 

Advantage of this classification : 

1) The systematic grouping of elements into groups made the study simple. 

2) Each period begins with the electron entering a new shell and ends with the complete filling of s and p-sub-shells of that shell.

Limitations of Mendeleeffs periodic table : 

1) Anomalous pair of elements : Certain elements of highest atomic weights precede those with lower atomic weights. 

Eg : Tellurium (atomic weight 127.6) precedes iodine (atomic weight 126.9). 

2) Dissimilar elements placed together : 

a) Elements with dissimilar properties were placed in same group as sub-group A and subgroup Bt 

Eg : Alkali metals like Li, Na, K, etc. of IA group have little resemblance with coinage metals like Cu, Ag, Au of IB group. 

b) Cl of VII A group is a non-metal and Mn of VII B group is a metal.

Method of overcoming the limitations of Mendeleeffs periodic table by modern periodic table : 

1. In modern periodic table, elements are arranged in the ascending order of their atomic numbers. So this arrangement eliminated the problem of anomalous series. 

Eg : Though Tellurium (Te) has more atomic weight than Iodine (I), its atomic number is one unit less compared to Iodine.

2. The elements with similar outer shell (valence shell) electronic configurations in their atoms are in the same column called group in modern periodic table. So the elements have similar properties overcoming the Mendeleeffs second limitation.

Modern periodic law : 

‘The physical and chemical properties of elements are the periodic function of the electronic configurations of their atoms”.

Construction of the long form periodic table : 

1. Based on the modern periodic law, the modern periodic table is proposed. 

2. This periodic table is known as long form of the periodic table. 

3. Long form periodic table is the graphical representation of Aufbau principle.

4. The modern periodic table has 18 vertical columns called groups and 7 horizontal rows known as periods. 

5. There are 18 groups, represented by using Roman numerals I to VIII, with letters A and B in traditional notation, (or) 1 to 18 by Arabic numerals. 

6. There are 7 periods. These periods are represented by Arabic numerals 1 to 7. 

7. The number of main shells present in the atom of particular atom decides to which period it belongs. 

8. First period consists 2 elements, 2nd and 3rd periods contains 8 elements each, 4th and 5th periods contains 18 elements each, 6 period contains 32 elements and 7th period is incomplete. 

9. The elements are classified into s, p, d and f block elements. 

10. Inert gases are placed in 18th group.

Given, mass of electron = 9.1 × 10⁻³¹kg

K. E. = 3.0 × 10⁻²⁵J

\(\because\) K. E. = \(\frac{1}{2}\)mv²

v = \(\sqrt{\frac{2K.E}{m}}\) = \(\sqrt{\frac{2\times3.0\times10^{-25}kg\,m^2s^{-1}}{9.1\times10^{-31}\,kg}}\)

= 812 ms⁻¹

Now, apply de-Broglie equation,

Wavelength, \(\lambda\) = \(\frac{h}{mv}\)

= \(\frac{6.626\times10^{-34}Js}{9.1\times10^{-31}kg\times812\,ms^{-1}}\)

= 8967 × 10⁻¹⁰m

= 896.7 nm

The square of the amplitude of the electron wave, i.e.,. \(\psi^2\)at any point gives probability of finding an electron at that point. The region around the nucleus which represents the electron density at different points is known as an orbital, so the wave function for an electron in an atom is known as orbital wave function.

\(\because\) mass of proton = 1.67 × 10⁻²⁷kg

K. E. = 5 × 10⁻²⁷

\(\because\) K.E = \(\frac{1}{2}\)mv²

\(\therefore\) v = \(\sqrt{\frac{2K.E}{m}}\)

= \(\sqrt{\frac{2\times5\times10^{-27}}{1.6\times10^{-27}}m/s}\)

= 5.98 m/s

Ernest Rutherford.

Bohr’s theory ignores de-Broglie concept of dual behaviour of election and also contradicts with the Heisenberg’s uncertainty principle. Whereas, Schrodinger equation is based on quantum mechanics which deals with the microscopic objects having dual behaviour like particle as well as wave.

The splitting of spectral lines in an electric field is called the Stark effect.

Electronic configuration of element with atomic no. 12- (2,8,2) 

K is 2 

L is 8 

M is 2

The orientation of the orbital with an external magnetic field determines the magnetic orbital quantum number.

The element which is mentioned is Calcium (Ca) it is located in the fourth period and second group.

Dobereiner made groups of three elements each, having similar chemical properties and called them triads. He arranged the three elements in a triad in an increasing order of atomic mass and showed that the atomic mass of the middle element was approximately equal to the mean or the atomic masses of the other two elements.

Examples : Lithium (Li), Sodiun (Na), Potassium (K) form Dobereiner’s triad.

After calcium, every 8th do not possess properties similar to that of the first.

It was assumed that only 63 elements existed in nature and no new elements would be discovered in the future. But later on several new elements were discovered whose properties did not fit into the law of octaves.

(i) The Law was applicable to elements up to Calcium (Ca) only.

(ii) Properties of new discovered elements did not fit into the law of octave

He could only find 3 triads in elements due to this his concept was discarded.

The total number of periods in modern periodic table is seven

The magnetic orbital quantum number takes values from – l to l.

(a) No, because all these elements do not have similar properties although the atomic mass of silicon is average of atomic masses of sodium (Na) and chlorine (Cl).
(b) Yes, because they have similar properties and the mass of magnesium (Mg) is roughly the average of the atomic masses of Be and Ca.

Wave: Surging movement of water, electricity, etc.

Spectrum: A spectrum is a group of wavelengths or frequencies.

Intensity: The amount of energy per unit volume is called intensity.

Line spectrum: The colours correspond to certain discrete wavelengths of light and are called Line spectrum. It Is also known as discrete spectrum.

Quantum numbers: The numbers indicate the probability of finding the electron in the space around the nucleus.

Shell (or) orbit: The path of an electron around the nucleus is called shell or orbit.

1. When two atoms come sufficiently close together the valence electrons of each atom experience the attractive force of the nucleus in the other atom. 

2. The nucleus and the electrons in the inner shell remain unaffected when atoms come close together. 

3. The electrons in outer most shell of an atom get affected. 

4. Thus electrons in valence shell are responsible for the formation of bond between atoms.

Correct option is  B) N > O

Correct option is  B) Oxygen

Sub-shells: Atomic orbitals are also called sub-shells.

Correct option is  B) Si, N

Correct option is  B) O

Option : a. 6.626× 10^-34Js

Option : b. dumbbell

Option : b. size of the orbital

Option : a. Pauli’s exclusion principle

The photosynthetic reaction which does not require light (lightindependent) is called dark reaction. A dark reaction occurs in the stroma portion of chloroplast so it is called stroma reaction. It is also called Blackman’s reaction. Dark reaction is influenced by temperature. The different chemical reactions of dark reaction are enzymatic. Enzymes of stroma catalyze these reactions. Enzymatic reactions of dark reaction occur in the form of a Cycle and they were studied by Melvin Calvin, Benson and Bassham in 1949. So dark reaction is also called Calvin cycle or Calvin Benson cycle. They used tracer technique by using C₁₄O₂ in unicellular alga Chlorella and found a path of CO₂ in each step of a chemical reaction. The ATP and NADPH of light reaction are used for the fixation of CO₂ during the dark reaction. The main event of dark reaction is the fixation of CO₂. So dark reaction is also called CO₂ fixation cycle.

Lactic acid fermentation is the process of anaerobic respiration which does not involve intake of oxygen (O₂ ) and release of carbon dioxide (CO₂ ).

Correct option is B) Carbon dioxide