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
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•
•
•
•
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
Ionization Energy
• The energy required to remove an electron
from an atom of an ion
Ionization Energy Trends
Electron Affinity
• The energy change that occurs when a neutral
atom gains an electron
Electronegativity
• A measure of the ability of an atom in a
compound to attract electrons
Electronegativity
• Why is the no color-coding for He, Ne, and Ar?