Unit 5 Test What You Need to Know !! A.Periodic Table History 1.Medeleev (original) ordered by atomic mass & Columns by similar chemical properties “periodic law” 2.Mosely (present) Ordered by atomic number B.Periodic Table Structure 1.Periods Horizontal row Valence e - s in same principal energy levels (PEL’s) Period number = number of outermost PEL 2.Group Vertical columns Same number of valence electrons Similar chemical properties Groups 1-12 are metals (alkai,alkaline, transition) Groups mix of metals, metalloids, nonmetals Groups 17- halogens Groups 18 – noble gases

Group 1 & Group 2 – ALKALI & ALKALINE EARTH METALS Highly reactive most reactive of metals more reactive as move down the group group 1 more slightly more reactive than group 2 Groups 3-12 – TRANSITION METALS Less reactive Some like gold (Au), platinum (Pt) and silver (Ag) are relatively unreactive Others like nickel (Ni), tin (Sn), iron (Fe), and aluminum (Al) are fairly reactive Form color ions in solution Hard except for mercury,Hg, (liq) High melting and boiling points METALLOIDS (SEMIMETALS) Exhibit properties of both metals & nonmetals along diagonal “staircase” in groups SI and Ge most widely known GROUP 17 – HALOGENS Highly reactive most reactive of nonmetals more reactive as move up the group Only group to exhibit all 3 phases of matter Exist as diatomic molecules each has distinctive color and odor GROUP 18 – NOBLE (RARE) GASES Highly nonreactive (inert) exist as monatomic gases Neon, Argon, Krypton used in lighting

FACTORS in PERIODIC TABLE TREND: A) Nuclear Charge: Number of protons in the nucleus. The larger the # of protons (atomic number) the greater the charge; the greater the charge the stronger the attraction for electrons. B) Electron Shielding: the layers of electrons between the nucleus and the outermost electron. These inner electrons shield the outermost electron from the full attractive force of the nucleus. The larger the number of the principal energy levels (PEL), the more layers of shielding. The more layers of shielding, the less the pull on the electron. C) Principal Energy Level: The higher the PEL level, the higher the electron energy. The higher the PEL level, harder for nucleus to attract outermost electrons L to R in Period decreasing metallic characteristics SOLID GAS Top to Bottom in Group SOLID increasing number of PEL’s increasing metallic properties increasing # of valence electrons

MetalNonmetals ionization energy lowhigh electro- negativity lowhigh form ion by losing e - ’s to form + positive ions (cations) gaining e - s to form negative ions (anions) ion radii compared to atom smaller larger conductabilityexcellentpoor state at room temperature solid except for Hg (liq) gas or solid except for Br (liq) workabilitygood; malleable & ductile poor; brittle appearancemetallic luster; shinydull period trendsmetallic character decreases L to R nonmetallic character increases L to R group trendsmetallic character increases down a group nonmetallic character decreases down a group Generalized Metal vs Nonmetal Comparisons “in summary …” allotrope – one of two or more different forms of an element in the same phase >(different physical & chemical properties) Ex Oxygen (O 2, O3), Carbon (graphite, diamonds)