Structure Of Atom

Electronic configuration gives the information regarding the manner in which electrons in an atom occupy the shells, sub shells and orbitals of that atom.

The short hand notation - nl^x - consists of principal energy level (n), the letter representing sub level (l) like s,p,d,or f and number of electrons in that sub level are written as superscript (x). example of hydrogen is given below-

If n is the number of principle energy shell, then maximum number of

electrons that can be accommodated is given as 2n² .

For first shell n = 1, so maximum number of electrons is 2(1)² = 2

Second shell n = 2 , so maximum number of electrons is 2(2)² = 8….so on

The maximum number of electrons that can be accommodated in a sub shell is 2(2l + 1), where l = 0,1,2,3…so on for s,p,d,f sub shells respectively.

For example,

i. s sub shell, l = 0 , number of electrons accommodated are 2

ii. p sub shell, l = 1 , number of electrons accommodated are 6……….so on

The maximum number of electrons that can be accommodated in an orbital is 2.

“s” sub shell has 1 orbital, so its occupancy is 2.

“p” sub shell has 3 orbitals, so its occupancy is 6 electrons and so on .

If n is the number of principle energy shell , n subshells are present in it.

For example first shell has one subshell , i.e. s subshell

Second shell (n = 2) has 2 sub shells , i.e. s and p sub shells

Third shell (n = 3) has 3 sub shells , i.e. s,p and d sub shells and so on…

Two spin orientations are possible for an electron in an orbital. Positive and

negative spin which are represented as + 1/2 and -1/2 respectively.

(a) M shell.

(b) 10 electrons. K shell has 2 electrons and L shell has 8 electrons. So, as given M shell has electrons equal to the number of electrons in K and L shells. So, its 2 + 8 = 10.

(c) Atomic number is equal to total number of electrons . so total electrons is equal to electrons in K, L and M shells, i.e. 2 + 8 + 10 = 20

(d) 1s²2s²2p⁶3s²3p⁶4s² – calcium

Rainbow is a natural spectrum of colors caused by the dispersion of sun light by tiny water droplets present in atmosphere. This spectrum has no sharp boundaries in between colors. It consists of different wavelengths with no gap. That’s why rainbow is an example of continuous spectrum.

Two elliptical orbits are added by Sommerfeld in third Bohr’s orbit. In an attempt to account for the structure (splitting) of line spectra known as fine spectra, Sommerfeld added these elliptical orbits.

The spectrum of electromagnetic radiation transmitted through a substance showing dark bands due to absorption at specific wavelengths is called absorption spectrum.

The region of space around a nucleus where the probability of finding an electron is maximum is called an orbital whereas Bohr’s orbits refer to the fixed defined paths around nucleus, which electrons follow based on their energies.

1. principle quantum number – n- determines the main shell which contains electron. Determines its distance from nucleus and its energy.

2. angular momentum quantum number – l – determines the sub shell in which electron is present, i.e. s or p or d or f sub shell .

3. magnetic quantum number – m- determines the orbital of electron in that sub shell.

The short hand notation – nl^x - consists of principal energy level (n), the letter representing sub level (l) like s,p,d,or f and number of electrons in that sub level are written as superscript (x). example of hydrogen is given below-

This is used to write electronic configuration of atoms of element.

Hund’s rule doesn’t support this. According to Hund’s rule electron pairing in orbital starts only when all available empty orbitals of same energy are singly occupied. Here, in 2p subshell, pairing started without electrons filling the other orbitals.

Aufbau’s principle is violated here. According to this principle electrons should fill orbitals in increasing order of energy. 1s has lower energy than 2s and 2p. so, electron filling should happen at 1s first followed by 2s and 2p.

Sodium atomic number is 11.

Its configuration is 1s²2s²2p⁶3s¹

The differentiating electron is 3s¹

n = 3

l = 0

m = 0

spin = -1/2 or + 1/2

In these cases, a completely full (d¹⁰) or half full (d⁵) d-orbital is more stable than a partially filled d sub shell, so an electron from 4s gets excited and rises to 3d orbital. This makes them stable.

Expected configurations based on Aufbau principle –

Cr – [Ar]4s²3d⁴

Cu – [Ar]4s²3d⁹

Actual configurations

Cr – [Ar]4s¹3d⁵

Cu – [Ar]4s¹3d¹⁰

The spectrum of frequencies (bright bands seen) of electromagnetic radiation emitted due to atomic transition in an element from high to low energy state.

(i) l = 0 means s sub shell, n = 2 means second principle shell.

So, its orbital lies in 2s (the one and only orbital in s subshell) with m = 0

(ii) n = 1, l = 0, m_l = 0 , m_b = + 1/2

L is at a higher energy level. Far the shell from nucleus, more is its energy. K represents shell 1, which is next to nucleus followed by L,M,N respectively. So, energy of K<L<M<N…..so on. Larger shells have more energy.

we know that

Where c = velocity of light =

λ = wavelength, given as 1m

μ = frequency = ?

so,

note: s^-1 = 1 Hz