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Chapter 4 THE PERIODIC TABLE HOW ARE ELEMENTS ORGANIZED? Groups of elements share certain properties PERIODIC PATTERN Newlands (1865) – Arranged elements according to increasing atomic mass Properties repeated every 8 elements Law of octaves Dobereiner (early 1800s) Groups Triads of 3 elements have similar properties MENDELEEV First periodic table 63 known elements at the time Mendeleev’s table contains gaps that unknown elements should fill He predicted the properties of these unknown elements & gave them names MOSELEY Arranged elements according to atomic number Erased the discrepancies in Mendeleev’s table OTHER CONTRIBUTIONS Seaborg – pulled out inner transition elements to condense periodic table Ramsey – discovered noble gases PERIODIC LAW Elements with similar properties appear at regular intervals (when arranged by atomic #) Valence electrons – outermost electrons in an atom of an element Electrons that participate in chemical reactions with other atoms GROUPS/FAMILIES & PERIODS Group/family = vertical column on the periodic table Elements have similar chemical properties because of same # of valence electrons Period = horizontal row Elements have same number of occupied energy levels (i.e. energy level 2) GROUPS AND PERIODS THE PERIODIC TABLE Main Group elements Transition elements Inner transition elements METALS, NONMETALS, METALLOIDS Metals – occupy the majority of the periodic table Located to the left of the “staircase” Lustrous, Malleable, Ductile, Conductors Alloy = a solid or liquid mixture of 2 or more metals Nonmetals – generally opposite properties of metals Metalloids – have properties of both, located along the “staircase” METALS, NONMETALS, METALLOIDS TRANSITION METALS d-block elements Groups 3-12 Do NOT have identical outer electron configurations May lose different #’s of valence electrons Good conductors, ductile, malleable LANTHANIDE & ACTINIDE SERIES f-block elements Lanthanides – first row of inner transition elements Shiny metals, similar in reactivity to alkaline earth metals Actinides – second row Radioactive 4f 5f ns2np6 ns2np5 ns2np4 ns2np3 ns2np2 ns2np1 d10 d5 d1 ns2 ns1 Ground State Electron Configurations of the Elements ALKALI METALS – GROUP 1A (GROUP 1) React with water to make alkaline solutions One valence electron = VERY reactive Lose their 1 valence electron to achieve noble gas configuration (octet) Soft texture, dull or shiny, good conductors Group 1A Elements (ns1, n 2) ALKALINE EARTH METALS – GROUP 2A (GROUP 2) Highly reactive 2 valence electrons Harder and have higher melting points than alkali metals Group 2A Elements (ns2, n 2) COMMON GROUP ELEMENTS – 3A TO 5A (GROUPS 13-15) 3, 4, or 5 valence electrons (depending on group) Some metals, some metalloids, some nonmetals Group 3A Elements (ns2np1, n 2) Group 4A Elements (ns2np2, n 2) Group 5A Elements (ns2np3, n 2) CHALCOGENS – GROUP 6A (GROUP 16) Oxygen group 6 valence electrons Name means “ore former” Nonmetals, metalloids, metals Group 6A Elements (ns2np4, n 2) HALOGENS – GROUP 7A (GROUP 17) Highly reactive nonmetals 7 valence electrons (1 short of a noble gas configuration) Often react with alkali metals “Salt maker” Group 7A Elements (ns2np5, n 2) NOBLE GASES – GROUP 8A (GROUP 18) Inert = unreactive 8 valence electrons (full set); except He (2 e-) HYDROGEN Most common element in the universe 1 electron Extremely flammable Reacts unlike any other element PERIODIC TRENDS Predictable change in a particular direction Reactivity of Alkali metals Increases as you down the group Reactivity of Halogens Increases as you go up the group IONIZATION ENERGY Energy supplied to remove an electron IE + X (g) X+(g) + e- Electron Shielding – outermost electrons are not held as tightly to the nucleus due to the inner electrons “shielding” them Filled n=1 shell Filled n=2 shell Filled n=3 shell Filled n=4 shell Filled n=5 shell General Trend in Ionization Energies Increasing First Ionization Energy Increasing First Ionization Energy ATOMIC RADIUS Atomic radius = ½ the distance from the center to the center of 2 like atoms that are bonded Atomic Radii ELECTRONEGATIVITY Ability of an atom in a compound to attract electrons Fluorine has highest electronegativity value ELECTRON AFFINITY Electron affinity = energy change when a neutral atom gains an electron ION SIZE Cation is always smaller than atom from which it is formed. Anion is always larger than atom from which it is formed. Comparison of Atomic Radii with Ionic Radii