The atomic mass of an element is the average mass of the atoms of an element measured in atomic mass unit (amu, also known as daltons, D). The atomic mass is a weighted average of all of the isotopes of that element, in which the mass of each isotope is multiplied by the abundance of that particular isotope. (Atomic mass is also referred to as atomic weight, but the term 'mass' is more accurate.)
For instance, it can be determined experimentally that neon consists of three isotopes: neon-20 (with 10 protons and 10 neutrons in its nucleus) with a mass of 19.992 amu and an abundance of 90.48%, neon-21 (with 10 protons and 11 neutrons) with a mass of 20.994 amu and an abundance of 0.27%, and neon-22 (with 10 protons and 12 neutrons) with a mass of 21.991 amu and an abundance of 9.25%. The average atomic mass of neon is thus:
Se 34 S 16 O 8 Tm 69 Md 101 (258) Erbium 167.26 Fermium 15 Bi 83 Sb 51 As 33 P 15 N 7 Er 68 Fm 100 (257) Holmium 164.930 Einsteinium 14 Pb 82 Sn 50 Ge 32 Si 14 C 6 Ho 67 Es 99 (252) Dysprosium 162.50 Californium 13 Tl 81 In 49 Ga 31 Al 13 B 5 Dy 66 Cf 98 (251) Terbium 158.925 Berkelium 12 Hg 80 Cd 48 Zn 30 Tb 65 Bk 97. Periodic Table of the. Silicon is a chemical element with atomic number 14 which means there are 14 protons and 14 electrons in the atomic structure.
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|0.9048||×||19.992 amu||=||18.09 amu|
|0.0027||×||20.994 amu||=||0.057 amu|
|0.0925||×||21.991 amu||=||2.03 amu|
The atomic mass is useful in chemistry when it is paired with the mole concept: the atomic mass of an element, measured in amu, is the same as the mass in grams of one mole of an element. Thus, since the atomic mass of iron is 55.847 amu, one mole of iron atoms would weigh 55.847 grams. The same concept can be extended to ionic compounds and molecules. One formula unit of sodium chloride (NaCl) would weigh 58.44 amu (22.98977 amu for Na + 35.453 amu for Cl), so a mole of sodium chloride would weigh 58.44 grams. One molecule of water (H2O) would weigh 18.02 amu (2×1.00797 amu for H + 15.9994 amu for O), and a mole of water molecules would weigh 18.02 grams.
The original periodic table of the elements published by Dimitri Mendeleev in 1869 arranged the elements that were known at the time in order of increasing atomic weight, since this was prior to the discovery of the nucleus and the interior structure of the atom. The modern periodic table is arranged in order of increasing atomic number instead.
The periodic table is an arrangment of the chemical elements ordered by atomic number so that periodic properties of the elements (chemical periodicity) are made clear.
Se Periodic Table Element
Explore the chemical elements through this periodic table
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The standard form of the periodic table shown here includes periods (shown horizontally) and groups (shown vertically). The properties of elements in groups are similar in some respects to each other.
There is no one single or best structure for the periodic table but by whatever consensus there is, the form used here is very useful and the most common. The periodic table is a masterpiece of organised chemical information and the evolution of chemistry's periodic table into the current form is an astonishing achievement.