JEE MAIN 2020 NEWS
NATIONAL LEVEL ONLINE TEST
Atomic Structure is one of the essential chapters included in the syllabus of JEE Main. Almost 2-4 questions are necessarily asked in the exam. The Atomic structure helps a lot in understanding the meaning of different terms such as Atomic mass, Atomic Radius, Size of an atom, Electronic Configuration, Orbitals, and its Structure, etc. These terms are widely used while understanding other chapters such as Periodic Table and Chemical Bonding as well.
In the year 1803, Dalton explained a theory regarding the composition of matter. According to the theory, an atom is defined as the smallest part of matter that is a part of the chemical reaction. According to Dalton’s atomic theory, the law of conservation of mass, law of constant composition and law of multiple proportions very successfully, but are unable to come to any conclusion in many experiments. Further modern studies revealed that an atom is not indivisible but can be broken down.
All the objects around you, including book, pen, table, or something else constitute the matter of the universe. The matter is any substance that takes a particular space and has mass. According to Dalton, the matter is made up of very small, indivisible particles known as atoms. The concept which was proposed in 1808, was accepted for many years.
The main postulates of Dalton’s atomic theory include:
However, according to many types of researches done by many renowned scientists and the discovery of radioactivity created confusion; it was doubted that atom was not only the tiniest indivisible particle but it also has challenging complex structures of its own and were made up of smallest particles such as electrons, protons, neutrons, etc. Almost 35 different subatomic particles are known but three particles namely electron, proton, and neutron were considered as the fundamental particles.
The existence of electrons in atoms was first proposed by J.J. Thomson, after experimenting with the conduction of electricity through gases at low pressures and high voltage. The e/m ratio for cathode rays is certain with the value of 1.76 x 108 C/g
Atom is electrically neutral, in case it contains negatively charged electrons then it also contains some positively charged particles. The same theory was confirmed by Goldstein in his discharge tube experiment with the perforated cathode. When high voltage was passed between the electrodes of a discharge tube it was observed that some rays came from the directions of anode that later passed through the holes in the cathode. These anode rays include positively charged particles that were formed by ionization of gas molecules through cathode rays.
The charge to mass ratio of positive charge is maximum when the tube gets filled with hydrogen gas as hydrogen is the lightest element. These positively charged particles are called protons. e/m differ based on the nature of gas taken in the discharge tube. The positive particles are positive residues of the gas left when the gas is ionized. The neutral charge particle, neutron was introduced by James Chadwick by shelling boron or beryllium with a–particles.
Practice with JEE Main Question Paper
The atoms are made by a combination of three fundamental particles. The charge and mass of these fundamental particles include:
|Approximate relative mass||1/1836||1||1|
|Mass in kg||9.109×10–31||1.673×10–27||1.675×10–27|
|Mass in amu||5.485×10–4||1.007||1.008|
|Actual Charge||4.8 × 10–10||4.8 × 10–10||0|
Postulate: – Atoms are a sphere of positive charge in between which the number of electrons is embedded.
Limitations: – This theory was unable to satisfactorily explain the results of the scattering experiment carried out by Rutherford.
Limitations: - This theory was unable to explain the stability and electronic structure of the atom.
Atomic Number (Z) – They are the number of protons or electrons of a neutral atom.
Mass Number (A) – It include the total number of protons and neutrons in an atom
Nucleons- Nucleons include protons and neutrons that are present in a nucleus. So, all these fundamental particles are being referred to as nucleons
Isotopes- Isotopes are atoms of the element that have the same atomic number but different mass number e.g. 1H1, 1H2, 1H3.
Isobars- Isobars are the atoms with the same mass number but different atomic numbers, e.g. 15P32 and 16S32
Isotones- They are the atoms with the same number of neutrons but different number of protons or mass number, e.g. 6C14, 8O16, 7N15
Isoelectronic- Isoelectronic are the atoms, molecules, or ions that have same number of electrons.
Wavelength (λ) – It is the distance between two neighboring troughs or crests.
Frequency (ν) - It is the number of times a wave passes through a given point in a medium in one second. ν = c/λ
Velocity (c) = Velocity is the distance traveled by the wave in one second. c = νλ
Wave number = It is the number of wavelengths per cm.
Amplitude (a) = Amplitude is the actual height of the crest or depth of the trough. It helps in determining the intensity of the beam of light
JEE Main Chemistry section carries a weightage of 30-40 % and is considered an important section in one of the most popular entrance exams. This section helps to understand a lot about chemistry and also modern physics. Almost 2 to 3 questions are asked from this section every year in the JEE Advanced and 1 to 2 questions in JEE Mains. The candidates with a good understanding of topics have higher chances of getting a good score in the JEE exams. So study harder to ace the exam!!