The modern periodic table
Atomic number and protons
The The number of protons in the nucleus of an atom. Also called the proton number. of an A substance made of one type of atom only. was originally just its position on the periodic table. After the discovery of Subatomic particle with a positive charge and a relative mass of 1. The relative charge of a proton is +1., scientists realised that the atomic number of an element is the same as the number of protons in its The central part of an atom. It contains protons and neutrons, and has most of the mass of the atom. The plural of nucleus is nuclei..
In the modern periodic table, the elements are arranged according to their atomic number - not their The mean relative mass of the atoms of the different isotopes in an element. It is the number of times heavier an atom is than one-twelfth of a carbon-12 atom.. This fixed the problems of tellurium (52) and iodine (53) which are in the wrong order if sequenced by relative atomic mass.
In the periodic table the elements are arranged into:
- rows, called A horizontal row in the periodic table., in order of increasing atomic number
- vertical columns, called A vertical column in the periodic table containing elements with similar chemical properties., where the elements have similar The characteristics of something. In chemistry, chemical properties include the reactions a substance can take part in. Physical properties include colour and boiling point.
