Saturday 27 December 2008

Atomic Number and Mass Number of Atom (Nomor Atom dan Nomor Massa Atom)

Every element have a different number of protons. The number of protons is atomic number. Beside protons, in an atom consist of electrons and neutrons. In neutral atom, number of protons is equal to number of electrons. The number of electrons determine the properties of atom.
the number of protons and neutrons which located in nucleuscalled as mass number of atom. The mass of protons and neutrons is atomic mass because the mass of electron is too small, so can be neglected. The atom of an element expressed by the following symbol:

where:
X = the symbol of atom
A = mass number of atom
Z = atomic number
Example: the symbol of C atom given by , so:
mass number of atom = A = the number of protons and electrons = 12
atomic number = the number of protons = the number of electrons = 6
the number of neutrons = A - Z = 12 - 6 = 6

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Setiap atom memiliki jumlah proton yang berbeda. Jumlah proton yang kita sebut sebagai nomor atom. Selain proton, di dalam atom juga terdapat elektron dan neutron. Dalam atom netral, jumlah proton sama dengan jumlah elektron. Jumlah elektron inilah yang menentukan sifat-sifat suatu atom.
Jumlah proton dan neutron yang terletak dalam inti atom disebut sebagai nomor massa atom. Massa proton dan neutron dianggap sebagai massa atom karena massa elektron terlalu kecil sehingga dapat diabaikan. Atom suatu unsur biasanya dilambangkan sebagi berikut:

dimana:
X = lambang atom
A = nomor massa atom
Z = nomor atom
Contoh: atom C memiliki lambang , maka:
nomor massa = A = jumlah proton dan neutron = 12
nomor atom = jumlah proton = jumlah elektron = 6
jumlah neutron = A - Z = 12 - 6 = 6

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