PERIODIC TABLE Chapter 5 Section 4

Dmitri Mendeleev Elements in columns in order of increasing atomic mass and rows according to similar properties. Developed the periodic table.

Henry Moseley Found atomic number. Listed elements in order of atomic number NOT mass.

Modern Periodic Table Element identified by symbol. Atomic number on top. Atomic mass and name at bottom. Listed in order of increasing atomic number, from left to right and from top to bottom. Periodic Law—when elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties.

Parts of the Periodic Table Periods—horizontal rows. Group—vertical columns (same physical and chemical properties).

PERIODIC TABLE DETAILS Group A—representative elements, exhibit a wide range of physical and chemical properties. Group B—transition metals and inner transition metals (in the valley).

Representative Elements Group 1-A—react vigorously with water and are called Alkali Metals. Group 2-A—Alkaline Earth Metals Metals (left side)—high electrical and heat conductivity, high luster when clean, ductile, and malleable.

More Representative Elements Group 7-A—Halogens Group 8-A or 0—Noble Gases, few chemical reactions. Non-metals (upper right corner)—gases, brittle, solid @ room temp., generally nonlustrous, poor conductors of electricity (insulators). Metalloids (along the stair step)—dull, brittle, semi-conductors, in between metals and nonmetals.

Atomic radii The size of the atom Increases moving down the group/family (adding an energy level) Decreases moving across the period (Charge of the nucleus increases, pulling in the electrons more)

Electronegativity The ability of an atom in a molecule to attract a shared electron pair to itself Atoms want 8 valence electrons. Called the octet rule. Metals lose electrons (become cations) to fill the outer energy level Nonmetals gain electrons (become anions) to fill the outer energy level

Ionization energy The energy needed to remove an electron. Some atoms will not give up the electrons. (nonmetals) Some give up electrons easily. (metals)

Most reactive metal is Francium Most reactive nonmetal is Fluorine