Basic Chemistry The Periodic Table

The Periodic Table Organized by Dmitri Mendeleev 1869 to illustrate periodic trends in the known elements In its present form, the periodic table allows us to identify properties of elements and their trends

The Periodic Table http://en.wikipedia.org/wiki/File:Periodic_table.svg

Periods & Families The rows or periods of the periodic table tell us how many energy levels are found in atoms of each element The columns or families (also called groups) show us the general properties of each element – how its atoms combine with other elements, how it reacts, etc.

Atomic Number & Atomic Mass The atomic number tells us how many protons are in each atom The mass number tells us how many total protons and neutrons are found in an average atom Some atoms have more or fewer neutrons than average – this is why the number is expressed as a decimal 23 V Vanadium 50.942

Energy Levels The number of electrons in a neutral atom equals the number of protons Electrons are arranged in different energy levels Each energy level can hold a maximum number of electrons The outermost one can never hold more than 8 http://elements-ri2p11.wikispaces.com/file/view/Xenon_Electron_Configuration.png/198914080/Xenon_Electron_Configuration.png

Families and Valences The number of electrons in the outermost energy level tells us how atoms can combine with other atoms to make compounds All atoms “want” to have a complete outer level and will lose, gain, or share electrons to accomplish this The number of electrons an atom usually gains or loses is called its valence number

Valence Numbers You can figure out an element’s valence number by looking at which column or family it is found in +1 +2 +3 4 -3 -2 -1 Varies

Other Periodic Table Information Notice the zigzag line on the table – elements to the left are metals; those to the right are nonmetals; those on the line are metalloids Nonmetals Metalloids Metals

Compounds When atoms of different elements join together, they form compounds Generally, compounds formed from a metal and a nonmetal are called ionic compounds Those formed from two or more nonmetals are called covalent compounds We will discuss these compounds and how they are formed in the next part of this unit