An element is defined by the IUPAC as a pure chemical substance composed of atoms with the same number of protons in the atomic nucleus. All atoms of an element have the same number of protons.
| Fact to remember | Name of the element |
|---|---|
| Atoms of elements can have different number of electrons and neutrons. | |
| A variant of an element with different number of neutrons is known as its | Isotope |
| Different physical form of an element is known as its (e.g. graphite and diamond) | Allotrope |
| Element most abundant in the Universe | Hydrogen |
| Element most abundant in the human body | Oxygen |
| Element which forms more than 10 million compounds | Carbon |
| Element with the lowest melting and boiling point | Helium |
| Element with the highest melting point | Carbon |
| Element with the highest boiling point | Tungsten |
| Element with highest density | Osmium |
| Element with lowest density | Hydrogen |
| Element with highest electronegativity | Flourine |
| Element with lowest electronegativity (highest electropositivity) | Francium |
| The first element to be produced artificially | Technitium |
| The most corrosion resistant element (which cannot be affected by water, chemicals or acids) | Iridium |
| The element which was discovered on the Sun before it was found on the Earth | Helium |
| The non-metallic element which is liquid at room temperature | Bromine |
| The metallic element which is liquid at room temperature | Mercury |
| The most reactive element | Flourine |
The Periodic Table was created to organize and categorize the known chemical elements based on their properties and to understand the relationship between the elements.
| The Periodic Table was created by Dmitry Mendeleyev, a Russian chemist and professor in 1869. |
| The table created by Mendeleyev had 63 known elements. He arranged these elements based on their atomic weights and chemical elements. The table had gaps for elements which could be discovered in future. |
| The modern periodic table has seven rows or periods. |
| It has room only for 118 elements. The last element with atomic number of 118 is Oganesson |
| Lanthanides is a group of 15 elements from atomic number 57 to 71. Together with Scandium and Yttrium they are known as rare earth elements. |
| Rare earth elements which are 17 in number are actally not rare. Most of them are commonly found |
| Actinides is a group of 15 elements from atomic number 89 to 103. All actinides are radioactive. |
| The modern periodic table has 18 columns or groups. Some important groups are listed below. |
| Group 1 - Alkali metals or Lithium group consists of Lithium, Sodium, Potassium, Rubidium, Cesium and Francium. Hydrogen is not an alkali metal even though it is listed in the first column. |
| Group 2 - Alkaline earth metals or Beryllium group consists of Beryllium, Magnesium, Calcium, Strontium, Barium and Radium. |
| Group 15 - Pnictogens or Nitrogen group consists of Nitrogen, Phosphorus, Arsenic, Antimony, Bismuth and Moscovium. |
| Group 16 - Chalcogens or Oxygen group consists of Oxygen, Sulphur, Selenium, Tellurium, Polonium and Livermorium. |
| Group 17 - Halogens or Flourine group consists of Flourine, Chlorine, Bromine, Iodine, Astatine and Tennessine. |
| Group 18 - Noble gases or Helium or Neon group consists of Helium, Neon, Argon, Krypton, Xenon, Radon and Oganesson. |