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Atomic Structure of Isotopes
Nucleons are the components of the nucleus of an atom. A nucleon can either be a proton or a neutron. Each element has a unique number of protons in it, which is described by its unique atomic number. However, several atomic structures of an element can exist, which differ in the total number of nucleons.
These variants of elements having a different nucleon number (also known as the mass number) are called isotopes of the element. Therefore, the isotopes of an element have the same number of protons but differ in the number of neutrons.
The atomic structure of an isotope is described with the help of the chemical symbol of the element, the atomic number of the element, and the mass number of the isotope. For example, there exist three known naturally occurring isotopes of hydrogen, namely, protium, deuterium, and tritium. The atomic structures of these hydrogen isotopes are illustrated below.
The isotopes of an element vary in stability. The half-lives of isotopes also differ. However, they generally have similar chemical behavior owing to the fact that they hold the same electronic structures.
Atomic Structures of Some Elements
The structure of atom of an element can be simply represented via the total number of protons, electrons, and neutrons present in it. The atomic structures of a few elements are illustrated below.
Hydrogen
The most abundant isotope of hydrogen on the planet Earth is protium. The atomic number and the mass number of this isotope are 1 and 1, respectively.
Structure of Hydrogen atom: This implies that it contains one proton, one electron, and no neutrons ( total number of neutrons = mass number – atomic number)
Carbon
Carbon has two stable isotopes – 12C and 13C. Of these isotopes, 12C has an abundance of 98.9%. It contains 6 protons, 6 electrons, and 6 neutrons.
Structure of Carbon atom: The electrons are distributed into two shells and the outermost shell (valence shell) has four electrons. The tetravalency of carbon enables it to form a variety of chemical bonds with various elements.
Oxygen
There exist three stable isotopes of oxygen – 18O, 17O, and 16O. However, oxygen-16 is the most abundant isotope.
Structure of Oxygen atom: Since the atomic number of this isotope is 8 and the mass number is 16, it consists of 8 protons and 8 neutrons. 6 out of the 8 electrons in an oxygen atom lie in the valence shell.
Heisenberg’s uncertainty principle: Heisenberg stated that no two conjugate physical quantities can be measured simultaneously with 100% accuracy. These will always be some error or uncertainty in the measurement.
Drawback: Position and momentum are two such conjugate quantities that were measured accurately by Bohr (theoretically).
Stark effect: Phenomenon of deflection of electrons in the presence of an electric field.
Zeeman effect: Phenomenon of deflection of electrons in the presence of a magnetic field.
Dual Nature of Matter
The electrons which were treated to be particles, the evidence of photoelectric effect shows they also have wave nature. This was proved by Thomas young with the help of his double slit experiment.
De-Broglie concluded that since nature is symmetrical, so should be light or any other matter wave.
Quantum Numbers
- Principal Quantum number (n): It denotes the orbital number or shell number of electron.
- Azimuthal Quantum numbers (l): It denotes the orbital (sub-orbit) of the electron.
- Magnetic Quantum number: It denotes the number of energy states in each orbit.
- Spin Quantum number(s): It denotes the direction of spin, S = -½ = Anticlockwise and ½ = Clockwise.
Electronic Configuration of an Atom
The electrons have to be filled in the s, p, d, f in accordance with the following rule.
- Aufbau’s principle: The filling of electrons should take place in accordance with the ascending order of energy of orbitals:
- Lower energy orbital should be filled first and higher energy levels.
- The energy of orbital α(p + l) value it two orbitals have same (n + l) value, E α n
- Ascending order of energy 1s, 2s, 2p, 3s, 3p, 4s, 3d, . . .
- Pauli’s exclusion principle: No two electrons can have all the four quantum numbersto be the same or if two electrons have to be placed in an energy state they should be placed with opposite spies.
- Hund’s rule of maximum multiplicity: In the case of filling degenerate (same energy) orbitals, all the degenerate orbitals have to be singly filled first and then only pairing has to happen.