Question

1. State Morden Periodic law?
2. What is Electromagnetic Spectrum ?
3. Why Alkali Metals do not occur free state in nature ?
4. State the following

a) Pauli's Exclusion principle
b) Hund's rule of maximum multiplicity ​​​​​​
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Answer 1

1. The chemical and physical properties of elements are periodic functions of their atomic number. This is called the modern periodic law.

2.The electromagnetic spectrum is a continuum of all electromagnetic waves arranged according to frequency and wavelength.

3.Alkalimetals are highly reactive because of their high electropositivity and lower ionisation
enthalphies. Hence they occur in combined state but not in free state.

4a) Pauli exclusion principle

• According to this principle, an orbital can have maximum two electrons and these must have opposite spins.
• In other words, no two electrons in an atom can have all the four quantum numbers exactly the same.
• As we know that fourth quantum number is m, 1/2 is spin up and -1/2 is spin down and hence if the first three quantum numbers are same for two electrons then the electrons must have opposite spins in an orbital.

4b) Hund's Rule Of Maximum Multiplicity

It states that,pairing of electrons in the orbital belonging to the same subshell does not take place until each orbital belonging to that subshell has got one electron each ,ie, it has to be singly occupied first,after that pairing of electrons takes place.