The Periodic Table

Periodic Law 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.

Periods – a horizontal row of elements in the periodic table. Tells you how many energy levels an atom has. Ex. Lithium has two energy levels Group (family) – a vertical column of elements in the periodic table. Tells you the number of electrons in the outer electron shell. Ex. Lithium has one electron in outer electron shell.

Some Atoms Form Ions Ionization – the process of adding electrons to or removing electrons from an atom or group of atoms. Ion – an atom or group of atoms that has lost or gained one or more electrons and therefore has a net electric charge. Cation – an ion with a positive charge. Anion – an ion with a negative charge.

How are elements classified? Metals – the elements that are good conductors of heat and electricity. Nonmetals – the elements that are usually poor conductors of heat and electricity. Semiconductors – the elements that are intermediate conductors of heat and electricity.

Metals Alkali metals – the highly reactive metallic elements located in Group 1 of the periodic table. Soft and shiny and reacts violently with water. Very reactive because it has one valence electron that can easily be removed to form a positive ion. Not found in nature as elements Combine with other elements to form compounds Ex. – salt NaCl

Alkaline-earth metals Make up the second column of elements from the left edge of the periodic table. Have two valence electrons. Less reactive than alkali metals but still react to form positive ions with a 2+ charge. Combine with other elements to form compounds.

Transition metals The metallic elements located in Groups 3-12 of the periodic table. Much less reactive than other metals Some form as many as four differently charged cations because of their complex arrangement of electrons. All metals conduct heat and electricity. Can be stretched and shaped without breaking.

Nonmetals Most are located on the right side of the periodic table. Plentiful on Earth Oxygen, nitrogen, and sulfur may form compounds or gain electrons to form negative ions. Gases in the air are nonmetals

Halogens The highly reactive elements located in Group 17 of the periodic table. Seven valence electrons. Poisonous gases unless in a compound with the negative ion.

Nobel gases The unreactive gaseous elements located in Group 18 of the periodic table. Have eight valence electrons. Full octet “happy”