Guided Tour of the Periodic Table

PProperties of elements tend to change in a regular pattern when elements are arranged in order of increasing atomic number, or number of protons in their atoms. HHow does this pattern appear when put into a table?

 Groups   Periods  Groups (also called families) are the vertical columns of elements in the periodic table Periods are the horizontal rows of elements in the periodic table

 Periodic Table Applet Periodic Table Applet

 Remember: The valence electrons are the ones at the outermost energy level of an atom  Remember: There are usually the same number of protons as electrons in an atom and no overall charge  An ion is an atom that has gained or lost electrons from its valence shell and therefore has a positive or negative charge  Most atoms LOVE to have a full valence shell

Lithium atom 0 charge Lithium ion +1 charge Ions that have a positive charge are called “cations”

Fluorine atom 0 charge Fluorine ion -1 charge Ions that have a negative charge are called “anions”

 Atomic number (Z): # of protons in an atom  Atomic mass: # of protons and neutrons in an atom (why isn’t it a whole number?)

An isotope is any atom having the same number of protons, but having different numbers of neutrons within its nucleus Atomic mass (amu) Atomic number

SSubtract the (rounded) atomic number from the atomic mass of the atom: ## neutrons = atomic mass – Z EExample: Calculate the number of neutrons contained in a Sodium atom (Z = 11) and mass = amu RRound amu to 23 amu 223 amu – 11 = 12 neutrons SSodium contains 12 neutrons.

 Atomic number: 11  Name: Sodium  Symbol: Na  Family: Alkali Metals  Seldom found as a pure element in nature. A soft metal that can be cut with a butter knife, it reacts violently with chlorine to produce table salt. Explodes in water, producing hydrogen gas and sodium hydroxide (drano)

 Atomic number: 12  Name: Magnesium  Symbol: Mg  Family: Alkaline Earth Metals  A common ingredient found in fireworks and in metal alloys

 Atomic number: 13  Name: Aluminum  Symbol: Al  Family: Other metals  Mined from earth in the mineral bauxite. Light, recyclable, but not very strong. The oxidized form of the element is the basis of rubies and sapphires

 Atomic number: 14  Name: Silicon  Symbol: Si  Family: Semiconductors  The third most abundant element in the earth. The oxidized form of this element is the basis for glass. Used widely in the electronics industry for its use in integrated circuits

 Atomic number: 15  Name: Phosphorus  Symbol: P  Family: Nonmetals  An essential component in living systems. Originally extracted from urine, but is obtained through phosphate minerals nowadays. The white variety catches fire spontaneously in air and water won’t wash the burning material from the skin. For this reason, it was first used as a weapon during World War I and continues to be used in warfare today.