Chapter 4

Learning Objectives Understand the development and need for the periodic table Identify the properties and locations of families on the periodic table Identify trends of atomic properties

Dmitri Mendeleev 1869 63 known Elements Arranged by atomic mass

Henry Moseley 1913 Organized elements by atomic number rather than atomic mass

Modern Versions – all follow the periodic law Theorodore Benfrey - 1960 Timothy Stowe

ADOMAH – good for electron config.

Why do the properties of elements repeat themselves at regular intervals? Valence Electrons

Groups Periods

Main-Group Elements Wide range of properties Solids, liquids, gases About half are metals Many are very reactive, some are not reactive Silicon and oxygen account for four of every five atoms found on or near Earth’s surface

Group 1 – Alkali Metals React with water to form alkaline solutions One valence electron – very reactive Not found in nature as pure elements Metals are very soft, easily cut with a knife Good conductors of electricity

Group 2 – Alkaline-Earth Metals Slightly less reactive than alkali metals (still very reactive) Two valence electrons Harder than alkali metals, higher melting points Last one in the family, Radium is radioactive

Metals Excellent conductors of electricity Conductors of heat Some are ductile (can be drawn into a wire) Some are malleable (can be hammered or rolled into sheets) Mg Sr Hg

Transition Metals Group members do not have identical electron configurations May lose different numbers of valence electrons during reactions Less reactive than Group 1&2 Gold, platinum, and palladium are the least reactive TMs Good conductors of heat Ductile and malleable

NonMetals C, N, O, P, S, Se Not good conductors of heat or electricity Brittle No metallic luster Most abundant elements on earth

Metalloids B, Si, Ge, As, Sb, Te, Po Behave like nonmetals chemically and physically Electrical conductivity like metals Semiconductors – conduct electricity weakly

Group 7 - Halogens Most reactive group of non-metals Seven valence electrons (one short of stable) F2, Cl2 are gases at RT Br2 is a liquid at RT I2 and At2 are solids at RT

Group 8 – Noble Gases Also known as noble gases Mostly unreactive Full set of electrons in outer shell

Lanthanides and Actinides Fill “f” orbitals Called Lanthanides because they follow Lanthanum on the periodic table Actinides follow – Actinium All actinides are radioactive (unstable nuclei) Shiny metals Similar in reactivity to alkaline-earth metals

Atomic Radius How do you measure the radius of an atom?

Atomic Radius One way - Bond Radius

Atomic Radius Trends Why? Increasing energy levels Why? Increasing nuclear charge pulls electrons inward

Ionization Energy The energy required to remove an electron from an atom of an ion

Ionization Energy Trends Father from nucleus Why? Electron Shielding Why? Increasing nuclear charge, harder to remove an electron

Electron Affinity The energy change that occurs when a neutral atom gains an electron Father from nucleus Why? Electron Shielding Why? Increasing nuclear charge, goal is to be complete

Electronegativity A measure of the ability of an atom in a compound to attract electrons Father from nucleus Why? Electron Shielding Why? Increasing nuclear charge, stronger (+) attraction

Electronegativity Why is the no color-coding for He, Ne, and Ar?