Introduction to the Periodic Table

I. Development of the Table A. Dobereiner (1829) placed elements in triads-groups of 3 based on similar characteristics. 1. When he grouped elements with similar properties he found a relationship with atomic mass.

Halogen Triad ElementSymbol Atomic mass ChlorineCl35.5 BromineBr80 IodineI127 These 3 elements have similar properties. ( )/2 = 81.2

B. Mendeleev (1869) 1. Arranged elements by increasing atomic mass in columns, starting with the lightest.

Mendeleev’s Periodic Table

3. Significance of Mendeleev’s table Showed that element properties display periodicity-the tendency to recur at regular intervals Showed that element properties display periodicity-the tendency to recur at regular intervals He predicted the properties of several undiscovered elements. (blank spaces) He predicted the properties of several undiscovered elements. (blank spaces) Ex: Tellurium

C. Moseley & The Modern Periodic Table 1. Rearranged the periodic table by increasing atomic number 2. Periodic Law- physical & chem properties of elements repeat in a regular pattern when arranged in order of increasing atomic # Ex: atomic radius

II. Using the Periodic Table A. Period- horizontal row B. Group (family)- vertical column members of the same family have the same # valence e - members of the same family have the same # valence e - They have similar chem properties They have similar chem properties

C. The Groups of the Periodic Table

Group 1: Alkali Metals 1 valence 1 valence The most reactive elements The most reactive elements Never found uncombined in nature Never found uncombined in nature Soft, shiny metals Soft, shiny metals Na is so reactive it must be packaged in oil Na is so reactive it must be packaged in oil Na

Group 2: Alkaline Earth Metals 2 valence 2 valence 2 nd most reactive elements 2 nd most reactive elements Never found uncombined Never found uncombined

Transition Metals Found in the middle of the periodic table Found in the middle of the periodic table Don’t always have the same # valence Don’t always have the same # valence Example: Sometimes Cu has 1 valence and sometimes it has 2. Example: Sometimes Cu has 1 valence and sometimes it has 2.

Group 13: Boron Family 3 valence 3 valence B is a metalloid, the rest are metals B is a metalloid, the rest are metals Ex: Al Ex: Al

Group 14: The C family 4 valence 4 valence C is so abundant it has a whole branch of chemistry called organic chemistry C is so abundant it has a whole branch of chemistry called organic chemistry Si is in glass, cement, computer chips Si is in glass, cement, computer chips Sn & Pb Sn & Pb

Group 15: Then N family 5 valence 5 valence N 2 makes up 78% of the atmosphere N 2 makes up 78% of the atmosphere N & P are used as fertilizer and are cycled N & P are used as fertilizer and are cycled As As

Group 16: The O family 6 valence 6 valence O is very reactive O is very reactive Ex: S Ex: S

Family 17: The Halogens 7 valence 7 valence Most reactive nonmetals Most reactive nonmetals Form salts when they react with metals Form salts when they react with metals Ex: NaCl Usually gain 1 e Usually gain 1 e Ex: Cl & I Ex: Cl & I

Family 18: Noble Gases Have full valence Have full valence Most stable elements Most stable elements Ex: He, Ne Ex: He, Ne

Rare Earth Metals found at bottom Lanthanide series Lanthanide series Actinide series Actinide series Radioactive Radioactive Most don’t occur in nature Most don’t occur in nature Enriched Uranium

D. Physical State & Classes of Elements 1. Physical States a. Most elements are solid

b. 2 liquids = Br & Hg c. All gases are in the upper right except H. Br

2. Metals, nonmetals & metalloids a. Most elements are metals

Metals 1. Have luster 2. High melting pt 3. Conduct heat & electricity

4. Malleable 5. Ductile 6. Solid at room temp except Hg 7. Lose e when they bond

8. Are subject to corrosion – the deterioration of a material as a result of reaction with its environment, especially with oxygen

Nonmetals Opposite of metals in all properties Opposite of metals in all properties Are brittle Are brittle Are often insulators Are often insulators Share or gain electrons when they bond Share or gain electrons when they bond Many are gases Many are gases

Metalloids Have characteristics between a metal & a nonmetal. Have characteristics between a metal & a nonmetal. Are semiconductors- conduct heat & electricity, but not as good as a metal Are semiconductors- conduct heat & electricity, but not as good as a metal

Ex: Silicon