Structure of the Atom - Notes, Topics, Formula, Books, FAQs
The structure of atoms is a very important topic for understanding the physical and chemical properties of various atoms and molecules. Scientists tried to explain the atomic structure from time to time and gave various models of atoms like Dalton's model, Thomson's model, Bohr's model, etc. The electronic configuration of atoms provides insights related to various chemical reactions of elements. The important topics of the structure of atoms class 11 are mentioned below in this article.
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- Important Topics Of Atomic Structure
- Atomic Structure Overview:
- Line spectrum of hydrogen
- Quantum numbers:
- Atomic structure formula:
- How To Prepare The Atomic Structure
- Books For Atomic Structure:
- Some Solved Examples
Atomic structure is a fundamental topic to be studied in chemistry and modern physics. Atoms are extremely important particles that makeup all the materials on Earth. Atoms are present in our bodies and they bond together to form molecules, which make up matter. Everything in the universe is composed of individual atoms of various elements that combine together to form molecules. The basic structure of an atom consists of a nucleus containing protons and neutrons and a cloud of electrons revolving around the nucleus.
In this chapter, the aspirant will learn some important and basic terms electrons, protons, neutrons, atomic number, mass number, isotopes, isobars, velocity, frequency, wavelength, wavenumber, orbitals, quantum numbers, etc.
Important Topics Of Atomic Structure
Thomson Atomic Model:
Thomson had just discovered electrons in 1897, and this was actually the first model to try speaking about the internal configuration of atoms. This is commonly referred to as the "plum pudding model.". Thomson Atomic Model has many postulates which tell about the model.
Rutherford Atomic Model And Its Limitations:
The Rutherford Atomic Model, proposed by Ernest Rutherford, had several limitations like it could not explain the stability of atoms, it did not explain how electrons are arranged inside the atom, and many more.
Electromagnetic Radiation:
Electromagnetic Radiation refers to the transmission of energy through oscillating electric and magnetic fields at the speed of light
Planck's Quantum Theory:
Planck's Quantum Theory states that energy can only be absorbed or emitted by atoms and molecules in discrete quantities which is called Quanta.
Photoelectric Effect:
The Photoelectric Effect is the emission of electrons from a material caused by electromagnetic radiation such as ultraviolet light.
Bohr's Model Of An Atom:
Bohr's Model Of An Atom is a model that describes an atom as a small, positively charged nucleus surrounded by negatively charged electrons in circular orbits.
Hydrogen Spectrum:
The Hydrogen Spectrum is the line spectrum emitted by a hydrogen atom when an excited hydrogen atom returns to its ground state.
De Broglie Relationship:
The De Broglie Relationship describes the relationship between a particle's wavelength and its momentum. It was introduced in 1924 by French physicist Louis de Broglie.
Quantum Numbers:
The Quantum Numbers, are those which describe the location of an electron in an atom. They determine the properties of atomic orbital and electrons in that orbital.
Radial Nodes And Planar Nodes:
Radial Nodes and Planar Nodes are the regions in an orbit where the probability of finding an electron is zero. These are the spherical surfaces around the nucleus.
Frequency, Time Period, And Angular Frequency:
Frequency, Time Period, And Angular Frequency is the important topic of atomic structure. All these are parameters of periodic motion to define it completely. Frequency is defined as the number of vibrations per second or the number of complete oscillations per second. The time period is the time taken by a particular electron to revolve in a particular orbit.
Electronic Configuration:
Electronic Configuration describes the location of an electron around the nucleus of an atom. It is written by following the standard notation.
Stability Of Orbitals: Half-filled And Completely-filled:
Stability Of Orbitals: Half-filled And Completely-filled is the topic of atomic structure in which we study the stability of orbitals as Half-filled and completely-filled orbitals are more stable than other configurations because of symmetry and exchange energy.
Atomic Structure Overview:
In this chapter, the candidate will, first of all, know about the atomic theory proposed by Dalton in 1808 who regarded the atom as the indivisible particle of matter. At the end of the nineteenth century, it was proved that atoms are divisible and consist of three fundamental particles: Electrons, protons, and neutrons. Faraday then discovered electrons using a cathode ray discharge tube experiment. Neutrons were discovered by James Chadwick by bombarding a thin sheet of beryllium with $\alpha-$ particles. Various atomic models were proposed to explain the structure of the atom. The aspirant will know about Thomson's plum-pudding model, Rutherford's atomic model, and Bohr's model of an atom.
Line spectrum of hydrogen
When an electric discharge is passed through gaseous hydrogen, the $\mathrm{H}_2$ molecules dissociate and the energetically excited hydrogen atoms produced emit electromagnetic radiation of discrete frequencies. These radiations are emitted because of electronic transitions upon de-excitation to different energy levels and on the basis of the final energy level of transition, the hydrogen spectrum consists of several series of lines named after their discoverers like Lyman series, Balmer Series, Paschen Series, Bracket Series, Pfund Series.
Line Spectrum of Hydrogen-like atoms
$
\frac{1}{\lambda}=R Z^2\left(\frac{1}{n_1^2}-\frac{1}{n_2^2}\right)
$
Where $R$ is called Rydberg constant, $R=109677 \mathrm{~cm}^{-1}, Z$ is atomic number
$n_1=$ final orbit occupied after de-excitation $=1,2,3 \ldots$
$\mathrm{n}_2=$ initial orbit occupied before de-excitation
Lyman Series spectrum:
Transition of electrons from higher orbits to $n=1$ result in the Lyman Series
$
n_1=1 \text { and } n_2=2,3,4 \ldots
$
For the H atom, this lies in the Ultraviolet region. For elements with higher $Z$, the Balmer lines lie in the Ultraviolet region
Balmer Series Spectrum:
The transition of electrons from higher orbits to $n=2$ results in the Balmer Series
Where $n_1=2$ and $n_2=3,4,5,6 \ldots$
For H atom, this generally lies in visible region.
Paschen, Bracket and Pfund Series spectrums:
The transition of electrons from higher orbits to $n=3,4$ and 5 respectively result in the Paschen, Bracket and the Pfund Series
These lines lie in the Infrared Region for H atom.
The aspirant will also learn about Planck's quantum theory in which substances absorb or radiate energy discontinuously in the form of small packets. The phenomenon of the photoelectric effect in which there is the ejection of an electron from the surface of a metal when light of suitable frequency strikes on its surface is something very interesting to know in this chapter. Following it an aspirant will come across four quantum numbers like the principal quantum number, azimuthal quantum number, magnetic quantum number and spin quantum number including the shape and size of different orbitals.
The shape of s orbital: (spherical)
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The shape of p orbital:(dumbbell-shaped)
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The shape of the d orbital:
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Rules for filling of electrons in various orbitals is a very important part to be studied in this chapter which will be helpful in the rest of the chemistry portion especially in inorganic and organic chemistry.
Rules For Filling Orbitals:
Rule 1 - Aufbau's principle - Lowest energy orbitals are filled first. Thus, the order of filling $1 \mathrm{~s}, 2 \mathrm{~s}, 2 \mathrm{p}, 3 \mathrm{~s}, 3 \mathrm{p}, 4 \mathrm{~s}, 3 \mathrm{~d}$, etc.
Rule 2 - Pauli Exclusion Principle - Only two electrons are permitted per orbital and they must be of opposite spin.
Rule 3- Hund's Rule - No pairing of electron starts in any of the degenerate orbitals until all orbitals of the subshell contain one electron each with parallel spin.
Quantum numbers:
They are the set of four numbers that explain the state of electron i.e., location, energy, type of orbital, orientation of orbital, etc. in an atom. Various quantum numbers are as follows:
1. Principal quantum number( $n$)
2. Azimuthal quantum number($l$)
3. Magnetic quantum number( $m$ )
4. Spin quantum number($s$)
Atomic structure formula:
1. The velocity of the electron in nth Bohr orbit:
$v=2.18 \times 10^8 \frac{Z}{n} \mathrm{~cm} / \mathrm{sec}$
2. The radius of nth Bohr orbital:
$r_n=0.529 \frac{n^2}{z} A^0$
3. The total energy of an electron in nth orbit:
$E_n=-13.6 \frac{z^2}{n^2} \mathrm{eV}$
4. The kinetic energy of electron: -(total energy of electron):
$13.6 \frac{Z^2}{n^2} \mathrm{eV}=-\mathrm{P} \cdot \mathrm{E} / 2$
5.The potential energy of the electron:
$-27.2 \frac{Z^2}{n^2} \mathrm{eV}$
6. Line Spectrum of Hydrogen-like atoms
$
\frac{1}{\lambda}=R Z^2\left(\frac{1}{n_1^2}-\frac{1}{n_2^2}\right)
$
Where R is called Rydberg constant, $R=1.097 * 10^7$ where $\mathrm{Z}=$ atomic number.
7. De-Broglie wavelength
$\lambda=\frac{h}{m v}=\frac{h}{p}$
How To Prepare The Atomic Structure
The first and foremost thing a candidate should do is to read the NCERT book and be thorough with all the topics covered in this chapter. In order to get away with the confusion of "How to prepare for atomic structure" the aspirant can also take the help of animation and videos which are easily available on the internet, to understand the shape of orbitals, photoelectric effect, Bohr's model and other related topics. It is very important to have a clear picture of the experimental setup and observations in the mind of the candidate. The candidate should also focus on the previous year's question papers related to atomic structure. Based on analysis, it is found that most of the numerical problems are from Bohr's theory and the hydrogen spectrum. These are important topics from exam point of view. So, the candidate should try to solve as many problems from these two topics.
Books For Atomic Structure:
To prepare for atomic structure, these are some reference books that should be consulted;
1. J.DLee
2. O.P.Tandon
| Also read, |
Some Solved Examples
Example 1: When an electron jumps from $n=4$ to $n=2$ then the change in angular momentum is approximately.
1) $1.1 \times 10^{-34} \mathrm{Js}$
2) (correct) $2.2 \times 10^{-34} \mathrm{Js}$
3) $3.3 \times 10^{-34} \mathrm{Js}$
4) $4.1 \times 10^{-34} \mathrm{Js}$
Solution
The angular momentum of the electron in any $\mathrm{n}^{\text {th }}$ Bohr Orbit is given by
$
\begin{aligned}
& m v r=\frac{n h}{2 \pi} \\
& \Delta L=4\left(\frac{h}{2 \pi}\right)-2\left(\frac{h}{2 \pi}\right)=\frac{h}{\pi} \\
& \Delta L=\frac{6.626 \times 10^{-34}}{3.14}=2.2 \times 10^{-34}
\end{aligned}
$
Hence, the answer is the option (2).
Example 2: Which of the following statements is incorrect for Bohr's model of an atom?
1) (correct) It is valid for a multi-electronic species
2) Angular momentum of an electron is quantized
3) The centripetal force of attraction required for circular motion is provided by the electrostatic force of attraction between the electron and the nucleus
4) Orbits have fixed energy and are referred to as stationary states
Solution
Bohr's model is valid for only electronic species.
All other given statements given in the options are correct.
Hence, the answer is the option (1).
Example 3: The de-Broglie wavelength of a particle of mass 6.63 g moving with a velocity of $100 \mathrm{~ms}^{-1}$ is:
1) (correct) $10^{-33} \mathrm{~m}$
2) $10^{-35} \mathrm{~m}$
3) $10^{-31} \mathrm{~m}$
4) $10^{-25} \mathrm{~m}$
Solution
As discussed in concept:
De-Broglie wavelength:
$
\begin{aligned}
& \lambda=\frac{h}{m v}=\frac{h}{p} \\
& \text { - wherein }
\end{aligned}
$
where $m$ is the mass of the particle
V: its velocity
p: its momentum
So,
$
\begin{aligned}
& \lambda=\frac{6.625 \times 10^{-34}}{6.63 \times 10^{-3} \times 100} \\
& \lambda=10^{-33} \mathrm{~m}
\end{aligned}
$
Hence, the answer is the option (1).
Example 4: The electronic configuration of copper is:
1) (correct) $[\operatorname{Ar}] 3 d^{10} 4 s^1$
2) $[\operatorname{Ar}] 3 d^9 4 s^2$
3) $[\operatorname{Ar}] 3 d^{10} 4 s^2$
4) $[\operatorname{Ar}] 3 d^8 4 s^2$
Solution
Ideally, the electronic configuration of Cu must be [Ar] $3 d^9 4 s^2$ but in this case, the electrons in d-orbitals are not symmetrically filled. Thus to maintain the symmetricity, one electron from the 4 s -orbital goes to the d-orbital and thus Cu maintains the electronic configuration as $[A r] 3 d^{10} 4 s^1$.
Hence, the answer is the option (1).
Frequently Asked Questions (FAQs)
Atoms are made of Protons, Neutrons and Electrons.
In a neutral atom, the number of electrons are equal to number of protons.
Proton is almost 1850 times heavier than electron.
The structure of atom was discovered inititally by John Dalton.
Isotopes are variants of a particular chemical element that have the same number of protons but different numbers of neutrons. This means they have the same atomic number but different mass numbers.
Electrons are arranged in energy levels around the nucleus. Each energy level can hold a specific maximum number of electrons. The first level holds up to 2 electrons, the second level can hold up to 8, the third level can hold up to 18, and so on, following the 2n² rule.
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19 Dec'24 09:43 PM