Atomic Mass

(1)

(2)

• The number of protons in the nucleus of the atom is equal to the atomic number (Z).

• Henry Moseley discovered the atomic number of each element using x-rays, which led to more accurate organization of the periodic table

(3)

• Mass number of an atom is equal to the sum of the number of protons and neutrons in the nucleus.

• Dimitri Mendeleyev classified the elements according to their

chemical properties, he noticed patterns were in order with the mass number of the atom.

(4)

• Mass of a neutron is 1.6749 10^–27 kg

• Mass of a proton is 1.6726 10^–27 kg

• Mass of an atom (mass number) is calculated as mass number = protons + neutrons

(5)

• The unit of the atomic mass is «atomic mass unit» abbreviated as «u»

or «amu»

• 1 amu is also equal to 1 Dalton (Da)

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• Atoms that have the same atomic number (number of protons), but different mass numbers (number of protons and neutrons) are called isotopes.

6 proton + 6 neutron,

6 proton + 7 neutron

•

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• Mass spectrometry is used to determine the mass of an atom or molecule.

• Isotopes are separated through mass spectrometry. One can distinguish between isotopes of a given element by mass

spectrometry. A mass spectrometer separates each isotope by mass number

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•

• v² = 2eV / m

• e / m = v / H.r

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• Mathematical principle of mass spectrometry is given below:

(9)

Serie a b

Lyman 1 2,3,4 …. UV

Balmer 2 3,4,5 …. Visible

Paschen 3 4,5,6 …. IR

Bracket 4 5,6,7 …. IR

Pfund 5 6,7,8 …. IR