The Atomic Composition

·       A dense, positively charged region made up of protons and neutrons is called nucleus.

·       Electrons are negative charges that are present in orbitals outside the nucleus.

·       Mass Number of an atom is the sum of proton and neutron present in the nucleus and it is represented by A.

·       Atomic number is represented by Z which is equal to the number of protons in an atom. Since, an atom is electrically neutral, number of protons is also equal to number of electrons.

·       Isotopes are atoms of the same element with different number of neutrons but same number of protons.

Properties of Isotopes

Ø  The outer shell of electrons influences chemical properties. Because isotopes still have the same number of electrons, these properties will not change.

Ø  The physical properties of an atom are determined by their nuclei. Properties such as density, rate of diffusion, melting, and boiling change as the number of neutrons changes which is also responsible for change in mass. 

Uses of Radioisotopes

Ø  Carbon-14 is used to determine the age of organisms. This is known as radiocarbon dating.

Ø  Iodine-131/Iodine 125 can be used to treat thyroid cancer and detect thyroid function. Iodine 125 is a gamma emitter that can treat prostate cancer and brain tumors.

Question: What is mass spectroscopy and on which factors it depends upon?

Answer: A mass spectrometer separates individual isotopes from a sample of atoms and calculates their masses. The deflection of ion depends on absolute mass of ion, charge on the ion, strength of magnetic field and velocity. To get detailed analysis on this topic visithttps://youtube.com/channel/UCoqI7C9rI2UbFPITF2bPgnQ. 

Calculation of Atomic Mass

We can calculate relative atomic mass using the following formula because relative atomic mass is the weighted average of the relative masses of an elements isotopes.

Ar = (relative isotopic mass1 * percent abundance1) + (relative isotopic mass2 * percent abundance2) … / 100

Electronic Configuration

Emission Spectrums

Photons emitted from atoms as excited electrons return to a lower energy level produce emission spectrum.

§  When electrons return from higher energy state to n = 1 then, the series is called Lyman Series and radiation produced is UV light.

§  When electrons return from higher energy state to n = 2 then, the series is called Balmer Series and it produces visible light.

§  When electrons return from excited state to n = 3, the series is called Paschen Series and infrared rays are emitted. 

Orbitals

Basically, these 3 rules control the electron filling capacity of the atom.

1.     Paulis Exclusion Principle states that no more than two electrons can occupy the same orbital, and that two electrons in the same orbital must spin in opposite directions.

2.     The Aufbau Principle states that electrons are assigned to the orbitals with the lowest energy first.

3.     Hunds Third Rule states that orbitals of the same sub-level should be filled singly first, then doubly. If a sub-level has more than one orbital available, electrons occupy different orbitals with parallel spins 

Subshells

Orbitals are divided into s, p, d and f subshells.

§  s: 1 orbital 2 electrons

§  p: 3 orbitals 6 electrons

§  d: 5 orbitals 10 electrons

§  f: 7 orbitals 14 electrons

§  s orbitals have spherical shape.

§  p orbitals have dumbbell shape.

Question: How to write an electron configuration?

Answer: Electronic configuration is written based on certain rules from the above mentioned 3 principles. To get detailed notes on electronic configuration, kindly checkhttps://youtube.com/channel/UCoqI7C9rI2UbFPITF2bPgnQ. 

Electrons in Atoms

First Ionization Energy

The energy required to remove one mole of electrons from one mole of gaseous atoms is called first ionization energy. It is given by

X (g)           X+ (g) + e-

 Factors affecting first ionization Energy

§  The ionization energy increases as the proton number increases. This is because having more protons in the nucleus means that the nucleus produces more attractive force, requiring more energy to remove an electron.

§  As the distance between positive and negative charges grows, the force of electrostatic attraction between them weakens rapidly. As a result, electrons in shells further away from the nucleus are more weakly attracted to it than those closer to it. Therefore, the energy required to remove an electron down the group decreases. 

§  The lower the electrostatic attractive forces between the nucleus and the outer electrons, the greater the shielding of outer electrons by the inner electron shells. As the number of full electron shells between the outer electrons and the nucleus increases, so does the ionization energy.

Graphs of successive ionization energies and its properties can be studied at https://youtube.com/channel/UCoqI7C9rI2UbFPITF2bPgnQ.

Calculation by I. E. by convergence line

The first ionization energy corresponds to the limit of convergence at higher frequency in an emission spectrum. Energy and wavelength can be calculated with the help of

c = νλ or E = hν

where,

·       E = energy

·       ν = frequency

·       λ = wavelength

·       h is Planck’s Constant = 6.63 * 10^(-34) J/s

·       c is speed of light = 3 * 10^8 m/s