First 20 Elements Of The Periodic Table: The atomic number and symbols are important in chemistry. The atomic number of elements gives us an idea about the atomic structure of elements ...

mass number = protons + neutrons. Name the first 20 elements. The first 20 elements of the periodic table are as follows: H – Hydrogen, He – Helium, Li – Lithium, Be – Beryllium ...

Mendeleev left blank spaces in his original periodic table so that he could properly line up the known elements. Gallium, element 31, was his first gap to be filled, in 1875. The star of a popular ...

Physicists have filled in some longtime blank spaces on the periodic table, calculating electron affinities of the lanthanides, a series of 15 elements known as rare earths. Physicists at Michigan ...