PERIODIC+TABLE

=__**THE PERIODIC TABLE OF THE ELEMENTS**__=

__ORGANISATION OF THE PERIODIC TABLE__ The periodic table is an organised collection of all the known chemical elements. It is one of the chemist’s most useful tools. In the table the elements are arranged in order of increasing atomic number. The vertical columns of the periodic table are called __groups__ and are numbered 1 to 18. Each element in a group has the same number of outer shell electrons. These are called valence electrons. Valence electrons are largely responsible for chemical reactivity, as they determine how likely the atom is to bond with other atoms to form other chemical compounds. Elements in the same group usually have similar chemical properties. For example Group 1 (alkali metals), Group 2 (alkaline earth metals), Group 17 (halogens) and Group 18 (noble or inert gases). In the periodic table elements are also arranged in a series of rows called periods so that those with similar properties appear in vertical columns. Elements of the same period have the same number of electron shells; with each group across a period, the elements have one more proton and electron. **__ASSESSMENT__** Go to your Ultranet assessment section and complete the assessment on 'Navigating the Periodic Table'.