Atoms
Introduction:
Every element is made up of tiny, invisible particles known as atoms. Every atom is a sphere in which the total mass is equally distributed and the nucleus is surrounded by negatively charged electrons. According to Dalton's Atomic Theory, all elements are made up of very small, invisible particles known as atoms. Atoms of the same element are identical, but atoms of different elements differ. According to Thomson's Atomic Model, the total mass is uniformly distributed and negatively charged electrons are randomly inserted. The atom is completely neutral. Rutherford made the following observations based on this experiment. The nucleus is a relatively small area that contains the whole positive charge and virtually all of the mass of the atom. Negatively charged electrons circle the nucleus in a variety of orbits. The entire negative charge on an electron equals the total positive charge on the nucleus. As a result, the atom as a whole is neutral. The electrostatic force of attraction between the electrons and the nucleus provides the centripetal force required by the electron for rotation. Louis-Broglie proposed the daring theory that matter must have a dual nature as well. He realised the duality theory for matter after making the following observations: Matter and electromagnetic radiation make up the entirety of the universe's energy. Nature is drawn to symmetry. Because radiation has a dual nature, the matter must have a dual nature as well. Every moving particle, according to the hypothesis, Broglie's has a wave associated with it. De-Broglie waves, often known as matter waves, are such waves.
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List of topics according to NCERT and JEE Main/NEET syllabus:
- Dalton's Atomic Theory.
- Thomson's Atomic Model.
- Limitations of Thomson's Atomic Model.
- Impact Parameter.
- Rutherford's Scattering Formula.
- Limitations of Rutherford Atomic Model.
- Bohr’s Atomic Model
- Hydrogen Spectrum Series
- Wave Model
Related Topics,
Important concepts and Laws:
Bohr’s Atomic Model
The angular momentum of an electron can be an integer multiple of (h / 2π) for certain non-radiating orbits called stationary orbits.
mvr = nh / 2π
where n = I, 2, 3,... is referred to as the principal quantum number.
Only when an electron jumps from one permissible orbit to another permitted orbit can energy radiation occur.
Energy of emitted photon
hv = E2 – E1
E1 and E2.are the energy of electrons in orbits, respectively.
The radius of an electron's orbit is determined by
$r=n 2 h 2 / 4 \pi 2 m K Z e 2 \Rightarrow r \propto n 2 / Z$
n = principle quantum number
h = Planck’s constant
m = mass of an electron
$\mathrm{K}=1 / 4 \pi \varepsilon$
Z = atomic number
e = electronic charge.
The electron's velocity in any orbit is determined by
$v=2 \pi K Z e 2 / n h \Rightarrow v \propto Z / n$
The frequency of an electron in any orbit is calculated as follows:
$v=K Z e 2 / n h r=4 \pi 2 Z 2 e 4 m K 2 / n 3 h 3$
The kinetic energy of an electron in any orbit is calculated as follows:
$$
\text { Ek }=2 \pi 2 m e 4 Z 2 K 2 / \mathrm{n} 2 \mathrm{~h} 2=13.6 \mathrm{Z} 2 / \mathrm{n} 2 \text { electron Volt }
$$
Potential energy of electron in any orbit is given by
$$
\begin{aligned}
& E p=-4 \pi 2 m e 4 Z 2 K 2 / n 2 h 2=27.2 \mathrm{Z} 2 / \mathrm{n} 2 \text { electron Volt } \\
& \Rightarrow E p=\alpha Z 2 / n 2
\end{aligned}
$$
The total energy of an electron in any orbit is calculated as follows:
$$
E=-2 \pi 2 m e 4 Z 2 K 2 / n 2 h 2=-13.6 Z 2 / n 2 \text { electron Volt }
$$
⇒$E p=\alpha Z 2 / n 2$
Each element produces a specific spectrum of radiation that is unique to that element. The line spectrum is a series of separate parallel lines that make up the spectrum.
The Lyman Collection When an electron jumps from orbit n = 2, 3, 4,... to orbit n = 1, a Lyman series is formed. This series belongs to the ultraviolet spectrum.
The Balmer Collection is a collection of works by Balmer When an electron jumps from a n = 3, 4, 5,... orbit to a n = 2 orbit, a Balmer series line is formed. This series is set in the visual realm.
Paschen Collection When an electron jumps from orbit n = 4, 5, 6,... to orbit n = 3, a line of Paschen series is formed. This series belongs to the infrared spectrum.
Series Brackett When an electron jumps from the n = 5,6, 7,... orbit to the n = 4 orbit, a Brackett series line is formed. This series belongs to the infrared spectrum.
Series Pfund When an electron jumps from orbit n = 6,7,8,... to orbit n = 5, a Pfund series is formed. This series belongs to the infrared spectrum.
NCERT Notes Subject wise link:
- NCERT Notes for class 12 Physics.
- NCERT Notes for class 12 Chemistry.
- NCERT Notes for class 12 Mathematics.
- NCERT Notes for class 12 Biology.
Importance of Atoms for class 12
Unit-8, Atoms, and Nuclei are covered in Chapter 12 of Class 12 Physics. According to the new CBSE curriculum, the total weightage of Unit-7 (Dual Nature of Radiation & Matter) and Unit-8 in the board exam is 12 marks. In admission examinations like JEE and NEET, Unit 8 is heavily weighted. It carries a weightage of 3% in NEET, and 1 or 2 questions from this unit are expected to appear in the JEE Main Exam. Full marks on your board examinations are feasible if you study and comprehend the ideas thoroughly. It is not difficult to achieve full marks in any chapter if you work hard. In terms of grades, the situation with Physics Chapter 12 is no different. Physics, as a scientific topic, is all about facts and figures, and in order to get this knowledge straight on your test paper, you'll need to have all of your ideas crystal clear, as well as a firm foundation that will give you the confidence to attempt and solve all of the problems properly.
- NCERT solutions for class 12 physics chapter atoms
- NCERT exemplar solutions for class 12 physics chapter atoms
- NCERT notes for class 12 physics chapter atoms
NCERT Solutions Subject wise link:
- NCERT solutions for class 12 Physics.
- NCERT solutions for class 12 Chemistry.
- NCERT solutions for class 12 Mathematics.
- NCERT solutions for class 12 Biology.
NCERT Exemplar Solutions Subject wise link:
Frequently Asked Questions (FAQs)
Thomson's Model is also known as Plum Pudding Model. From the beginning of Chapter 12 of Class 12 Physics, you will study about the many atomic model theories. The Thompson Model is one of them. The atom is said to be like a plum or a watermelon in this concept. There is a reddish orangish fleshy portion with seeds embedded in it, similar to watermelon or plum. Thompson believed that the positive charge of the atom is represented by the fleshy section, while the negatively charged electrons are represented by the seeds.
It was unable to explain the origin of hydrogen and other atoms' spectrum series, as well as large angle scattering of – particles.
During its orbital motion, an electron should generate energy in the form of an electromagnetic wave, according to Maxwell's electromagnetic wave theory. As a result, the radius of the electron's orbit would steadily decrease, eventually falling inside the nucleus, and the Rutherford atomic model will be unable to describe the atomic line spectrum.
The radius of the initial orbit of the hydrogen atom is defined as Bohr's radius. It has a value of 5.29 x 10-11m ~ 0.53 Å.
"Atoms" is the title of Chapter 12 of Physics in CBSE Class 12. The many atomic model theories developed by various physicists are explored in this chapter. Thomson's Model of Atom, Rutherford Atomic Model, and Bohr's Model of Atom, commonly known as Bohr's Theory, developed by Neil Bohr, are some of the model hypotheses explored.
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Questions related to
Correct Answer: Involvement with the complexities of the day to day life.
Solution : The correct option is 3.
Baconian liberal education is the involvement with the complexities of the day to day life.
Explanation:
It is stated that "The magnificent ideals that have ever haunted of though the human mind and given us our highest proofs of future immortality by reason of the impossibility of their fulfillment here are splintered into atoms by contact with life's realities."
- Baconian liberal education is clearly linked to everyday life.
Correct Answer: Avogadro made a distinction between atoms and molecules.
Solution : The correct option is Avogadro made a distinction between atoms and molecules.
Avogadro distinguished molecules from atoms for the first time in 1811. He also proposed Avogadro's Law: equal amounts of gas at the same pressure and temperature have the same number of molecules.
Correct Answer: To be in pursuit of the ideal in the company of immortals
Solution : The correct option is 1
Explanation:
As stated in the passage, "Why such thinkers fly to the solitude of their own thoughts, or he the silent companionship of the immortals and if they care to present their verse to the world that these views take a sombre and melancholy setting from "the pale cast of thought" in which they were engendered."
- Therefore, great thinkers enjoy spending time alone with their thoughts in order to pursue the ideal in the company of immortals.
Correct Answer: Isotopes
Solution : The correct answer is Isotopes.
Isotopes are those atoms which have the same number of protons but different numbers of neutrons.
For example- There are three isotopes of Hydrogen. They are Protium, Deuterium, and Tritium. Where Protium only has one electron and one proton, Deuterium has one electron, one proton, and one neutron, while Tritium has one electron, one proton, and two neutrons.
Correct Answer: In their thoughts, with an exceptional calm.
Solution : The appropriate response is 2.
In their thoughts, with an exceptional calm.
Explanation
"Why such thinkers fly to the solitude of their own thoughts, or he the silent companionship of the immortals and if they care to present their verse to the world that these views take a somber and melancholy setting from "the pale cast of thought" in which they were engendered." is mentioned.
- Therefore, great thinkers are happy to keep their ideas to themselves because if they share them with others, it will be obvious where their ideas came from—weak displays of thought.