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 knownElements

Arranged by atomic mass

Henry Moseley

• 1913• Organized elements by atomic number rather than atomic mass

Modern Versions – all follow the periodic law

TheorodoreBenfrey - 1960 Timothy

Stowe

ADOMAH – good for electron config.

Why do the properties of elements repeat themselves at

regular intervals?

Valence Electrons

Periods

Groups

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 nuclear charge pulls electrons inward

Why

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Ionization Energy

• The energy required to remove an electron from an atom of an ion

Ionization Energy Trends

Why? Increasing nuclear charge, harder to remove an electron

Why

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Electron Affinity

• The energy change that occurs when a neutral atom gains an electron

Why? Increasing nuclear charge, goal is to be complete

Why

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Electronegativity

• A measure of the ability of an atom in a compound to attract electrons

Why? Increasing nuclear charge, stronger (+) attraction

Why

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Electronegativity

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