The history of the atom begins with a Greek philosopher named Democritus around 450 B.C. He wondered what would happen if we cut a piece of matter, such as chalk, into smaller and smaller pieces. He thought that a point would be reached where matter could not be cut into further small pieces.
He called those pieces ‘atomos’. In the year around 1800, a British chemist named John Dalton revived Democritus’s early ideas about the atom. He did many experiments that provided evidence for atoms.
He researched the properties of compounds. He showed that a compound always consists of the same elements in the same ratio.
He also comes with Dalton's Atomic Theory. One of his theories states that All substances are made of atoms, and they are the smallest particles of matter. They cannot be further subdivided into smaller particles. However, in the early 20th century, some scientists like J.J Thomson, Rutherford, etc, showed that atoms can be further subdivided into smaller parts, and the three subatomic particles of an atom are proton, electron, and neutron.
The number of subatomic particles in an atom is three which includes Proton, Neutron, and Electron. Each of them is discussed below.
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Protons and Neutrons together make the nucleus of an atom and are also called nucleons. Proton was first discovered by Ernest Rutherford in the year 1919 when he was performing his gold foil experiment. He projected alpha particles (called helium nuclei) at gold foil, and the positive alpha particles were deflected. From that, he concluded that a proton exists in a nucleus and protons are the subatomic particles that are positively charged. The atomic number of an atom is the number of protons present in an atom. The mass of a proton is 1.676 x 10-24 gramsand the charge is 1.602 x 10-19 Coulombs.
Electron was discovered by John Thomson in the year 1897. They are the negatively charged subatomic particles that revolve around the nucleus of an atom and are located in an electron cloud, which is the area surrounding the nucleus of the atom. The electrons can be removed or gained by an atom to form an ion. These positive and negative charged ions come together to participate in chemical bonding.
The mass of an electron is negligible as compared to the mass of a proton. It is found to have a mass equal to (1/1837) times the mass of a proton. The charge of an electron is 1.602 x 10-19 Coulombs. The 3 subatomic particles of an atom also include Neutron.
Neutron was discovered by James Chadwick in the year 1932, They are located in the nucleus with the protons. Neutron along with protons make up the nucleons. They do not carry any charge like proton or electron. The neutron determines the isotope of an atom and its stability. The number of neutrons in an atom is not necessarily equal to the number of protons. The mass of a neutron is 1.676 x 10-24 grams and it is electrically neutral.
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The Greek philosopher Aristotle, who lived about 100 years after Democritus, rejected Democritus’s idea of atoms. In fact, He thought the idea of atoms was ridiculous and ideas were accepted for more than 2000 years. After that, Dalton’s theory of Atom come into existence.
1. Define Isotopes
Isotopes are atoms of the same element that have different numbers of neutrons but the same number of electrons and protons. Eg: Hydrogen, Oxygen, and Carbon.
2. Write the number of subatomic particles of hydrogen, subatomic particles of carbon, and subatomic particles of oxygen.
As we know the subatomic particles of atoms are proton, neutron, and electron So,
1. Element: Hydrogen
Atomic number: 1
The number of electrons: 1
The number of protons: 1
Number of Neutrons: 0 (Other isotopes of Hydrogen have one and two neutrons).
2. Element: Carbon
Atomic number: 6
The number of electrons: 6
The number of protons: 6
Number of Neutrons: 6 (Other isotopes of Oxygen have 6 and 7 neutrons).
3. Element: Oxygen
Atomic number: 8
The number of electrons: 8
The number of protons: 8
Number of Neutrons: 6 (Other isotopes of Oxygen have 9 and 10 neutrons).
3. What is the total number of subatomic particles? Calculate the charge of one mole of electrons.
The total number of subatomic particles is three, they are proton, neutron, and electron.
Atom as a whole is electrically neutral. But the charge on Electron is negative, Neutral in Neutron, and positive in the proton.
Charge on One mole of an electron can be calculated as:
1 mole = 6.022 x 1023 atomsand charge of one electron = 1.6022 x 10-19 C
Therefore, the charge of one mole of electrons = 1.6022 x 10-19 x 6.022 x 1023 = 9.65 x 104 C.