Fourth Lesson
Structure of Atoms
By end of the lesson you will learn about the following thing
# Fundamental particles
# Electron, proton, neutron
# Structure of atoms
# Atomic number
# Mass number
# Isotope
# The rules of writing atomic and mass number
# Rutherford’s atom model
# Limitations of Rutherford’s atom model
# Bohr’s atom model
# Electronic configuration of atoms
1.1 Fundamental particles
In Dalton’s atomic theory atoms are indivisible. But now it is standstill. In the end of nineteen hundreds century it is proved that you can divide atoms to more dumps particles. Atoms are structured by which dumps particles are called Fundamental particles. They are Electron, proton, neutron. So we should know about these particles details.
It is mentioned that these particle’s charge and mass is very low. For the privilege of work the scientists use relative value of these particles in view of absolute value.
Electron: Electron is the dumps particle of atom. Electrons absolute mass is very low and it is 9.11 X 10-28g. Its mass is the1/1838 segment of hydrogen atom’s mass. Its charge is negative and very low (-1.60 X 10-19Coulomb). As it is dumps, it is the unit of charge and relatively it is 1. Electron’s formula is e-.
Proton: if you unset a electron from hydrogen atom, there will have a proton. For this its formula is H+. Its charge is positive and it is 1.60 X 10-19. it is relatively 1. Proton’s mass is same as hydrogen atom’s mass.
Neutron: Neutron is charge less. So its name is Neutron. In 1932, James Chadwick discovered Neutron. Its absolute mass is 1.675 X 10-24g. Its symbol is n.
1.2 Structure of atoms
There have a question that Electron, proton, neutron stand amid of an atom. In 1911 Ernest Rutherford proved that atoms have a centre. It is nucleus. Proton and neutron stand with nucleus. So nucleus bears almost all charge and mass of atoms. Electron visits around the out side of nucleus. We know atoms are dumps but nucleus is more dumps. The radius of atoms is 10-8cm and the radius of nucleus is 10-15m.
Atomic number: how many protons stand in nucleus is called Atomic number. Its symbol is Z. It is a fundamental property of simple matters. There have 6 protons in carbon atom. So carbon’s atomic number is 6. There have 8 protons in oxygen’s atom. So oxygen’s Atomic mass is 8. Sodium atomic mass is 11. Magnesium’s atomic mass is 12. The more protons in atoms, the more electrons in atoms.
Mass number: The total number of protons and neutrons in nucleus is called Mass number. Its symbol is A. Chlorine have 17 protons and 18 neutrons. So its mass number is 35.
Isotope: The same simple matter but with different mass number atoms are called Isotope. Their chemical attributes are same. Hydrogen has tree Isotope. They are hydrogen, Deuterium, Tritium. Hydrogen mass number is 1. Deuterium mass number is 2. Tritium mass number is 3.
1.3 the rules of writing atomic and mass number
You can easily determine the number of atoms, neutrons, protons and electrons in atoms. If any atom’s atomic number is Z, there will have Z protons and Z electrons. If mass number is A, there will have A-Z neutrons. By type of charge you should add or remove electrons
To show atomic and mass number, amount of charge, number of atoms you should follow the following rules.
AZXm+-
Here A = Mass number
X = Matter’s symbol
Z = Atomic number
M+- = Amount of charges
1.4 Rutherford’s Atom Model
Scientist Rutherford compared the structure of atoms with a dumps solar kingdom. For this, his model is called solar model. Its main speeches are--------
(1) Atomic centre bears all positive charge. It also bears almost all mass of atoms. Its name is nucleus. It is very dumps.
(2) Atoms are disinterested in electrically. So the numbers of electrons stand outside of nucleus are same of nucleus’s positive charges.
(3) As like the planets, electros visit around the nucleus as like sun. The static electrical attraction between positive nucleus and negative electron and the electron ‘s eccentric forces are equal
1.5 Limitations of Rutherford’s atom model
It is true that Rutherford’s atom model gives a correct order about structure of atoms but it has some limitations. For this it is not available. The limitations are---------
Planets are disinterested in electrically. But electrons are negative ions. By the James clerk Maxwell electro-magnetic information, if any ions move in a circle way, the ions will emit energy continuously and will go to small radius to visit around nucleus and will fall down into nucleus. At last, it is not possible to separate electrons from nucleus. So Rutherford’s atom model is unavailable.
1.6 Bohr’s atom model
In 1913, Niels Bohr has given a correct model about structure of atoms. Its main postulates are-------
(1) Electrons move some admitted circle way around the nucleus. In standing a fixed circle way, no electron receives or emits energy. These circle ways are called energy level.
(2) By receiving fixed energy electron can move to high energy levels. By emitting fixed electron can move to law energy levels.
1.7 Electronic configuration of atoms
We know that there has 1 electron in a hydrogen atom; there have 2 electrons in a helium atom. Again there has an atom which has 109 electrons. But there have a question that how do electrons configure in the atoms.
Answer:
(1) Every atom has two or more energy levels. Every atom is marked by n. Here n is 1, 2, 3, 4……………..etc.
(2) An energy level is known as a Shell.
(3) Which Shell stands near the nucleus, its energy is very law. By enlarge distance you can get high energy Shell. Generally electron stands in law energy Shell. But when it earns more energy it will go to high energy Shell.
THE END
