1. MODERN DAY PERIODIC TABLES
are expanded beyond Mendeleev's initial 63 elements.
Most include 108 or 109 elements,
have retained the format of rows and columns,
elements of what we now call a 'period' were listed vertically by Mendeleev,
Chemical 'groups' are now shown vertically in contrast to their horizontal format in Mendeleev's table.

2. PERIODS
Are rows in the periodic table,
Are numbered 1-7,
All elements in a row have the same number of energy levels,

3. FAMILY OR GROUPS Are columns in the periodic table,
Are numbered 1-18, and with roman numerals IA-VIIIA, IB-IIIB
Share an outer –e configuration,
Have the same number of valence electrons,
React similarly in chemical reactions

4. VALENCE ELECTRONS
Are electrons found in the outermost “s” & “p” orbitals,
Are the electrons involved in chemical reactions,
Are the electrons that are gained, lost or shared in chemical bonding.

5. TYPES OF ELEMENTS Metals- alkali & alkali earth
Non-metals- includes:noble gases & halogens
Metalloids,
Representative elements,
Transition metals,
Inner transition metals- actinide & lanthinides