Atom and properties of fundamental particles of atom
▶️ Atoms are the basic units of matter. The term 'atom' has been derived from the Greek word 'atomos' meaning indivisible.
▶️ The fundamental particles of an atom are protons ,neutrons and electrons.
All these fundamental particles are composed of even smaller particles such as quarks. All commonly observable matter is composed of up quarks and down quarks. They are the ones that bundled together in triplets to form protons (two ups and a down )and neutrons (two downs and an up).
PROTONS
▶️ Protons are positively charged particles found within atomic nuclei.
▶️ Rutherford discovered them while conducting cathode ray tube experiment ( 1911 and 1919 ).
▶️ Protons are about 99.86% as massive as neutrons.
▶️ Proton is denoted by the symbol p+ and its relative charge is +1.
▶️ The number of protons in an atom is unique to each element.
For example:
Carbon has 6 protons
Hydrogen has one proton
Oxygen has 8 protons
▶️ The number of protons in an atom is referred to as the atomic number of that element.
▶️ The number of protons also determines the chemical behaviour of the element.
ELECTRONS
▶️ Electrons are negatively charged particles found in the pathways called orbitals.Electrons surround the atomic nucleus.
▶️ Electrons are tiny compared to protons and neutrons, over 1800 times smaller than a proton or a neutron.
▶️ J.J Thomson discovered the electron in 1897.
▶️ Electrons have a negative charge and are electrically attracted to the positively charged protons.
▶️ Electron is denoted by the symbol e - and its relative charge is -1.
▶️ The number of electrons is always equal to the number of protons present in an atom hence an atom is neutral.
Examples:
Carbon has 6 electrons
Hydrogen has one electron
Oxygen has 8 electrons
NEUTRONS
▶️ Neutrons are neutral particles found within atomic nuclei.
▶️ Existence of neutron was theorised by Rutherford in 1920 and discovered by James chadwick in 1932.
▶️ Neutrons are absent in hydrogen atom.
▶️ Neutrons mass is slightly larger than that of a proton.
▶️ Number of protons and neutrons present in an atom together is referred as atomic mass.
Atomic mass = number of protons + number of neutrons
▶️ Neutron is denoted by the symbol n° and its relative charge is 0.
Examples:
Nitrogen has 7 proton and 7 neutrons hence its mass number is 14.
Magnesium has 12 protons and 12 neutrons hence its mass number is 24.
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