Structure of Atom Test - 30

According to Bohr's theory, the electrons absorb or emit photons thus altering their energy while jumping to higher or lower orbits, i.e., during electronic transition. Hence statement B is false. Hence answer is option B.

The number of protons found in the nucleus of an atom of a given element is called atomic number. Elements are placed in periodic table according to their atomic number.

The electron configuration of an atom shows the number of electrons in each sublevel in each energy level of the ground state atom. 
Here, $$1s^2 2s^2 2p^6 3s^2 3p^2 3d^5 4s^1$$ is ground state electronic configuration of Cr.
Note: To write the electronic configuration a more convenient way is shown in figure below.

Number of protons in the nucleus $$=$$ Atomic number of an atom $$= 12$$

Hence option C is correct.

The electrons revolve around the nucleus only in certain fixed paths called orbits. They are K, L, M, N, etc. Each orbit consists of a fixed number of electrons. The electrons are distributed in the orbits according to the formula $$2n^2$$.

P has $$5$$ electrons in the second shell ($$n = 2$$) , thus the electronic configuration is: $$2,5$$ and atomic no. $$= 7$$ 
Q has $$5$$ electrons in the third shell ($$n = 3$$) , thus the electronic configuration is: $$2,8,5$$ and atomic no. $$= 15$$. 

It was in $$1913$$ that Neils Bohr put forth the stability of the atom and with the help of Planck's quantum theory explain the reason for spectral lines. Bohr first made use of quantum theory to explain the structure of atoms and proposed that the energy of electrons in an atom is quantized.

Niels Bohr introduced the atomic Hydrogen model in 1913. He described it as a positively charged nucleus, comprised of protons and neutrons, surrounded by a negatively charged electron cloud. In the model, electrons orbit the nucleus in atomic shells. The atom is held together by electrostatic forces between the positive nucleus and negative surroundings.

Bohr’s Postulates

1. An atom has a number of stable orbits in which an electron can reside without the emission of radiant energy. Each orbit corresponds, to a certain energy level.

2. An electron may jump spontaneously from one orbit (energy level E1) to the other orbit (energy level E2) (E2 > E1); then the energy change AE in the electron jump is given by Planck’s equation

∆E = E2-E1 = hv

Where h = Planck’s constant.

And v = frequency of light emitted.

3. The motion of an electron in a circular orbit is restricted in such a manner that its angular momentum is an integral multiple of h/2π, Thus

mvr = nh/2π, where m = mass of the electron

v = velocity of the electron

r = radius of the orbit an

n = an integer called principal quantum number of the electron.:

4. A special surface around nucleus which contained orbits of equal energy and radius was called shell. These shells are numbered from inside to outwards as 1, 2, 3, 4 etc. and called K, L, M, N etc., respectively.

Elements	Electronic Configuration	Block	Group	Period
$$Ge$$ (32)	$$[Ar]\ 3d^{10}\  4s^2\ 4p^2$$	d	14	4
$$As$$ (33)	$$[Ar]\ 3d^{10}\  4s^2\ 4p^3$$	d	15	4
$$Se$$ (34)	$$[Ar]\ 3d^{10}\  4s^2\ 4p^4$$	d	16	4