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Atoms and Isotopes

Atom: The smallest part of an element that still maintains the properties of the element.

Proton (p+) is positively charged subatomic particle of the atomic nucleus. The atomic number of an element represents the number of protons in the nucleus.

 Electron (e-) is negatively charged subatomic particle that moves through empty space surrounding an atom’s nucleus. It carries a negative one charge. In an atom, the number of electrons is the same as the number of protons. In a cation, the number of electrons is less than the atom. In an anion, the number of electrons is greater then the atom.

Neutrons (n°) is a neutral subatomic particle in the nucleus. The number of neutrons is the atomic number subtracted from the mass number.

In summary…

Number of Protons = Atomic Number
Number of Electrons = Number of Protons = Atomic Number
Number of Neutrons = Mass Number - Atomic Number

Isotopes are atoms of the same element with the same number of protons but a different number of neutrons. In nature, most elements are found as a mixture of isotopes. Its relative abundance (how much of each type of isotope) in any sample of any element is the same.

eg) A banana is a good source of potassium.
93.25% of potassium atoms gave 20 n°.
6.73% of potassium atoms have 22 n°.
0.012% of potassium atoms have 21 n°.

In any two bananas, the relative abundance is the same.


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