# First 20 Elements

The first 20 elements of the periodic table have been tabulated below along with their symbols and atomic numbers.

 Atomic Number Element Symbol 1 Hydrogen H 2 Helium He 3 Lithium Li 4 Beryllium Be 5 Boron B 6 Carbon C 7 Nitrogen N 8 Oxygen O 9 Fluorine F 10 Neon Ne 11 Sodium Na 12 Magnesium Mg 13 Aluminium Al 14 Silicon Si 15 Phosphorus P 16 Sulfur S 17 Chlorine Cl 18 Argon Ar 19 Potassium K 20 Calcium Ca

## What Information does the Atomic Number of an Element Provide?

The atomic number of an element provides insight into the number of protons that exist inside the nuclei of the atoms of that element and also into the number of electrons that surround these nuclei. For example, the atomic number of sodium is 11. This implies that the nucleus of the sodium atom contains 11 protons and is surrounded by a total of 11 electrons. Since the atomic number of an atom is equal to the number of electrons it contains, the electronic configuration of the element can be determined just by knowing its atomic number.

It is important to note that the number of neutrons that exist in the nucleus of an atom cannot be determined by its atomic number. Different isotopes of an element may have the same number of protons and electrons (since they have the same atomic number), but they may have varying numbers of neutrons. For example, a sodium atom may have 11, 12, or 13 neutrons (based on the isotope) but will always have 11 protons and 11 electrons.

## Why is Potassium denoted by the symbol ‘K’ and Sodium by the symbol ‘Na’?

The symbol of potassium is ‘K’ because it is derived from the medieval Latin name for the element, which was ‘Kalium’. Similarly, the symbol for the element sodium is ‘Na’ because it is used to denote its older name ‘Natrium’. Several other elements have symbols denoting their old names. A few such examples have been listed below.

• The symbol of iron is ‘Fe’, which denotes the Latin name ‘Ferrum’.
• The symbol of copper is ‘Cu’, which denotes the Latin name ‘Cuprum’.
• The symbol of silver is ‘Ag’, which denotes the Latin name ‘Argentum’.
• The symbol of tin is ‘Sn’, which denotes the Latin name ‘Stannum’.
• The symbol of antimony is ‘Sb’, which denotes the Latin name ‘Stibium’.
• The symbol of tungsten is ‘W’, which denotes the German name ‘Wolfram’.
• The symbol of gold is ‘Au’, which denotes the Latin name ‘Aurum’.
• The symbol of mercury is ‘Hg’, which denotes the Latin name ‘Hydrargyrum’.
• The symbol of lead is ‘Pb’, which denotes the Latin name ‘Plumbum’.

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