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General Science - Chemistry (Atoms and its Structure)

Written By STPORTAL on Sunday, March 18, 2012 | 2:46 PM


General Science - Chemistry (Atoms and its Structure):

The Structure of Atoms:
The nucleus (atomic nucleus) is the center of an atom. It is composed of one or more protons and usually some neutrons as well. The simplest atom of all, hydrogen, has one particle—called a proton—in its nucleus.

Proton is a subatomic particle with a positive fundamental electric charge of 1.6 × 10-19 coulomb and a mass of 938 MeV (1.6726231 × 10-27 kg, or about 1800 times the mass of an electron).

Neutron is a subatomic particle with no net electric charge and a mass of 940 MeV (very slightly more than a proton). Its spin is 1/2. The nucleus of most atoms (all except the most common isotope of Hydrogen, which consists of a single proton only) consists of protons and neutrons. Outside the nucleus, neutrons are unstable and have a half-life of about 15 minutes, decaying by emitting an electron and antineutrino to become a proton.

Electron (also called negatron, commonly represented as e−) is a subatomic particle which carries a negative charge. In an atom the electrons surround the nucleus of protons and neutrons in an electron configuration. The electron has a negative electric charge of -1.6 × 10-19 coulombs, and a mass of about 9.10 × 10-31 kg (0.51 MeV/c2), which is 1/1800 of the proton mass. When electrons move, free of the nuclei of atoms, and there is a net flow, this flow is called electricity, or an electric current

The nucleus (atomic nucleus) is the center of an atom. It is composed of one or more protons and usually some neutrons as well. The simplest atom of all, hydrogen, has one particle—called a proton—in its nucleus.

Proton is a subatomic particle with a positive fundamental electric charge of 1.6 × 10-19 coulomb and a mass of 938 MeV (1.6726231 × 10-27 kg, or about 1800 times the mass of an electron).

Neutron is a subatomic particle with no net electric charge and a mass of 940 MeV (very slightly more than a proton). Its spin is 1/2. The nucleus of most atoms (all except the most common isotope of Hydrogen, which consists of a single proton only) consists of protons and neutrons. Outside the nucleus, neutrons are unstable and have a half-life of about 15 minutes, decaying by emitting an electron and antineutrino to become a proton.

Electron (also called negatron, commonly represented as e−) is a subatomic particle which carries a negative charge. In an atom the electrons surround the nucleus of protons and neutrons in an electron configuration. The electron has a negative electric charge of -1.6 × 10-19 coulombs, and a mass of about 9.10 × 10-31 kg (0.51 MeV/c2), which is 1/1800 of the proton mass. When electrons move, free of the nuclei of atoms, and there is a net flow, this flow is called electricity, or an electric current.


Atomic Number:
The number of protons in an atoms nucleus is called the atomic number (Z), and determines which element the atom is (for example hydrogen, carbon, oxygen, etc.). In an atom of neutral charge, the number of electrons typically equals the atomic number.


Atomic Weight (A):
The atomic weight is the sum of neutrons and protons in the nucleus of the atom also called Mass Number.


Molecular Weight:
The molecular weight of a molecule is the sum of the atomic weights of the atoms making up that molecule. Thus the molecular weight of water (H2O) is 2 × 1.00794 (for two hydrogen atoms) + 15.9994 (one oxygen atom), or 18.01528.

Isotopes:
Isotopes are atoms of a chemical element whose nuclei have the same atomic number, Z, but different atomic weights, A. The word isotope, meaning at the same place, comes from the fact that isotopes are located at the same place on the periodic table. i.e. number of neutrons differs in the atomic nuclei. Isotopes are generally written as 12C or carbon-12, with the number denoting the total number of protons and neutrons in the atom. Four out of every five elements occur in nature as mixtures of isotopes.
Isobars have the same isotopic mass but different atomic number. e.g. Argon, Potassium and calcium 18Ar40, 19K40 , 20Ca40
Isotone contains the same number of neutrons but different numbers of protons.


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