Structure Of An Atom, Learn atom constituents, Atomic Numbers, Mass Number, Isotopes, and Isobars

Safalta Expert Published by: Noor Fatima Updated Mon, 24 Oct 2022 05:29 PM IST

Highlights

Here is important and relevant information regarding Class 9 Chapter Structure Of An Atom. Read the article to learn about the same. 

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Structure of an Atom: The invention of the atom was a novel beginning to a new and comprehensive world of science. However, small an atom be, it includes a plethora of significant concepts inside. Therefore, it is appropriately explained in the chapter structure of an atom of class 9. The chapter will help you understand important topics like different models of an atom, fundamental components of an atom, atomic number, distribution of electrons, mass number, and valencies. So, here we go.

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Let us begin and cover this topic of the CBSE class 9 syllabus. 

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Table of Content
Fundamental constituents of an atom
Atomic structure of Oxygen
Atomic structure of Helium
Atomic structure of Carbon
Rutherford’s model of an atom
Drawbacks of Rutherford’s model of an atom
Thomson’s Model of an Atom
Drawbacks of Thomson’s model of the atom
Bohr’s Model of an atom 
Distribution of Electrons in different shells
Valency
Atomic Number (Z)
Mass Number (A)
Isotopes
Isobars

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Fundamental constituents of an atom

An atom consists of 3 basic particles, namely protons, electrons, and neutrons. The nucleus of the atom has protons and neutrons. Here, Protons are positively charged, and neutrons are neutrons. The electrons are negatively charged and are located in the outermost shell, called the electron shell.

Protons
Protons were discovered by Ernest Goldstein in 1886. He discovered that the different conditions in a similar chamber, the anode released positively charged particles called Canal rays. These were later named protons.

Electrons
These negatively charged particles were discovered by J. J Thomson in 1897. He explained that the cathode towards the anode discharges negatively charged particles in a cathode ray experiment.

Neutrons
Neutrons were discovered by J Chadwick. He invented a subatomic particle with neutral nature and mass equal to protons in the nucleus of all atoms.
 

Atomic structure of Oxygen

The oxygen atoms involve 8 protons, 8 electrons, and 8 neutrons. The mass number of oxygen atoms is 16.
 

Atomic structure of Helium

Helium atom has 2 protons, 2 electrons, and 2 neutrons. The mass number of helium atoms is 2.

Also read:
Electric Charges and Static Electricity
Electric Charge
Conductors and Insulators
Basic Properties of Electric Charge
Forces between Multiple Charges
Charging by Induction
Magnetic effect of Electric Current
Electric Flux
Electric Dipole
Potential energy of a dipole in an external field
 

Atomic structure of Carbon

The carbon atom has 6 protons, 6 electrons, and 6 neutrons. The mass number of carbon atoms is 12.
 

Atomic structure of Hydrogen

The hydrogen atom has only one proton, one electron, and no neutrons. 

Different models of the structure of atoms
The discovery of atoms brought the formulation of multiple theories by many prominent scientists. Some of the important theories about the structure of an atom, as per the chapter, are discussed below-
 

Rutherford’s model of an atom

Rutherford carried out an experiment showering the alpha (α)-particles on a gold foil. He examined the rotation of the alpha (α)-particles after going through an atom and made some assumptions about the experiment. These assumptions are as follows-
  1. The particles turn aside 180 degrees after bombing the nucleus.
  2. The size of the nucleus is minute compared to the total size of the atom.
  3. Most of the atom space is vacant as the particles went through the gold foil without any obstacle.
  4. The electrons rotate in the centre in a specified course.
  5. The positively charged centre is known as the Nucleus, and all the mass of an atom exists in the centre.
  6. These are the postulates presented by Rutherford using scattering of alpha (α)-particles on a gold foil experiment.

Drawbacks of Rutherford’s model of an atom

Rutherford’s model presented a completely new model of the structure of the atom. However, there are some drawbacks to the model. These are as follows-
  1. The electrons rotate in an unbalanced path. They undergo acceleration, emitting energy. When the electrons orbit, they lose energy. As a result, these negatively charged particles would collapse into the nucleus. 
  2. This course would make an atom extremely unsteady while an atom is highly stable. 
  3. This model failed to explain the atomic number concept as it talked about only the presence of protons in the nucleus.

Thomson’s Model of an Atom

J. J Thomson suggested that the structure of an atom is the same as that of a Christmas pudding, where the negatively charged particles electrons are implanted like currants in the sphere. 

He suggested the following-
  1. The structure of an atom is a positively charged sphere that entrenches electrons in it.
  2. An atom is electrically neutral as the number of protons and electrons is equal.

Drawbacks of Thomson’s model of the atom

This model field explains the structure of protons and electrons in their arrangement. 
 

Bohr’s Model of an atom 

Bohr developed a model to get over the drawbacks of Rutherford’s model. He stated the following assumptions-
  1. An atom allows only a discreet amount of rotation for the electrons to rotate and make the outer arrangement of an atom.
  2. While rotating electrons do not lose energy in these orbitals or energy levels
  3. When the negatively charged particles move from one energy shell to another, the magnitude changes.

Distribution of Electrons in different shells

Bohr Bury's model recommended the structure of particles in different revolutions. Following are the rules to write the number of particles in diverse orbitals-
  1. The outermost path can hold a maximum number of 8 electrons 
  2. The formula 2n^2 gives the room to the maximum number of electrons intact shell n=1, 2, 3, 4 for K=2, L=8, M=18, N=32. 
  3. The electrons brim up the interior levels first as they abide by the stepwise brimming of orbitals.

Maximum number of electrons in L shell 
Second shell=8
Using the formula 2n^2 number of electrons in any shell can be determined.
 

Valency

The next significant topic in the structure of atoms is valency. The electrons in the outermost crust are called valence electrons. These valence electrons are liable for the valency of an atom.

Valency is the propensity of an item to react when the other atoms are of similar or different elements. The items that brim up the outermost courses reflect chemical activity in the valence electrons. This reactivity is liable for the creation of molecules between one or more atoms.

The valency turns nil for an atom when the outer bonds have eight negatively charged particles or no electrons to lose. The particle with eight negatively charged particles in the outermost shell is an octet. These molecules are mostly static in nature.
  • Magnesium (Mg)  with a configuration (2, 8, and 2) has a valency of two.
  • Oxygen (O)  with a configuration (2, 8, and 6)  has a valency of 2. 
  • Helium (He) contains two negatively charged elements in the outermost shell. Therefore, the valency turns to be 2.
  • Neon (Ne) with a configuration (2, 8, and 8) has 8 negatively charged elements.

Atomic Number (Z)

The nucleus of an atom contains Protons, and the atomic number is equal to the number of protons in one atom of an element. 
As the atom is electrically neutral in nature, the number of positively and negatively charged elements is the same. Symbol Z denotes an Atomic number. 
Understanding these significant points of the chapter Structure of an Atom will be helpful-
  • Number of protons in an atom = Atomic number (Z)
  • Number of Electrons in an atom = Atomic number (Z)
  • Number of Neutrons= Mass number A – Atomic number (Z)

Mass Number (A)

The Mass number signifies the total number of protons and neutrons in the nucleus of an atom. Symbol A denotes the Mass number. Symbol N indicates the Total numerous of neutrons.
Mass Number = Atomic Number + Number of Neutrons in the Nucleus of the Atom
A = Z + n°
The mass number is also referred to as the Nucleon Number. 
 

Isotopes and Isobars

Isotopes and Isobars are significant topics that you must learn about for having a better command of the chapter Structure of an Atom.

Isotopes

The items of similar elements with the same atomic number and different mass numbers are called Isotopes.
For example, Hydrogen contains three isotopes Protium, Deuterium, and Tritium. 

Isobars

The atoms with different molecules and the same mass number are called Isobars.
For example, in calcium, the Atomic number is 20 and in argon, the Atomic number is 18. The mass number of both these elements is the same, i.e., 40.
We hope that this blog provided you with all the information about the chapter structure of an atom. It will lend you a hand in understanding the Class 9 science syllabus in a better way. You can reach out to Safalta school online for taking assistance from experts regarding your studies.
 

What are the limitations of J. J Thomson’s model of an atom?

This model field explains the structure of protons and electrons in their arrangement. 

What are the shortcomings of Rutherford’s model of an atom?

Rutherford’s model presented a completely new model of the structure of the atom. However, there are some drawbacks to the model. These are as follows-
  • The electrons rotate in an unbalanced path. They undergo acceleration, emitting energy. When the electrons orbit, they lose energy. As a result, these negatively charged particles would collapse into the nucleus. 
  • This course would make an atom extremely unsteady while an atom is highly stable. 
  • This model failed to explain the atomic number concept as it talked about only the presence of protons in the nucleus.

What does Bohr’s model of an atom talk about?

Bohr Bury's model recommended the structure of particles in different revolutions. Following are the rules to write the number of particles in diverse orbitals-
  • The outermost path can hold the highest number of 8 electrons 
  • The formula 2n^2 gives the room to the maximum number of electrons intact shell n=1, 2, 3, 4 for K=2, L=8, M=18, N=32. 
  • The electrons brim up the interior levels first as they abide by the stepwise brimming of orbitals.

What is the structure of an atom?

An atom consists of 3 basic particles, namely protons, electrons, and neutrons. The nucleus of the atom has protons and neutrons. Here, Protons are positively charged, and neutrons are neutrons. The electrons are negatively charged and are located in the outermost shell, called the electron shell.

Can an atom be destroyed?

According to the law of conservation of energy, matter can neither be created nor destroyed. Therefore, an atom cannot be destroyed.

What are the three parts of an atom?

An atom consists of 3 basic particles, namely protons, electrons, and neutrons. The nucleus of the atom has protons and neutrons. Here, Protons are positively charged, and neutrons are neutrons. The electrons are negatively charged and are located in the outermost shell, called the electron shell.

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