Chapter 5
The Periodic Table
Organizing The Elements
Before 1750, only 17 elements known
By 1860’s, 63 elements known
Dmitri Mendeleev (Russian Scientist)
•He arranged the elements by increasing atomic mass
•Elements with similar properties were in the same columns
Periodic Table: is the arrangement of elements into columns, based on properties that
repeat row after row.
There were “holes” (undiscovered elements) in Mendeleev’s Table
Mendeleev’s Table helped predict the discovery of
•Gallium
•Scandium
•Germanium
The Modern Periodic Table
The modern periodic table is arranged by increasing atomic number
114 known elements
Periods: are the horizontal rows on the table
First 3 rows represent the energy levels
•1st Level = holds up to 2 electrons
•2Nd Level = holds up to 8 electrons
•3rd Level = holds up to 8 electrons
•Technically 18
Properties
differ greatly as you move across a period
Groups (Families): are the vertical columns on the periodic table. (18 groups)
Elements within groups have similar properties
•Valence patterns
•Physical properties (color, etc.)
Periodic Law: is the pattern of repeating properties on the periodic table
Reactivity
Family: elements at the top are the least reactive, elements become more reactive as you
move down in a family
Periods: elements on the far right (noble gases) are NON-REACTIVE, elements on the
left are more reactive
Atomic Mass
Average Atomic Mass: is the average mass of all of an element’s isotopes
(remember to round when calculating the number of neutrons)
Atomic Mass Units
Atomic Mass Units: unit assigned to measuring the mass of protons, neutrons, and
electrons (rounded atomic mass)
Abbreviated as A.M.U.
Classes of Elements
Metals:
Good conductors of heat and electricity
Solid at room temp. (except mercury)
Malleable: hammered into thin sheets
Ductile: drawn into wire (copper)
Luster: metals have a shine
Oxidation: metals react with oxygen (rust)
Nonmetals:
Poor conductors of heat and electricity
Some solids, liquids, gases at room temp.
Brittle: nonmetal solids are not malleable or ductile (they break easily)
Nonmetals do not have a luster (shine)
Nonmetals do not oxidize
Metalloids:
Elements along the staircase
These are elements that show properties of both metals and nonmetals
Silicon = semi-conductor (computers)
Valence Electrons
Valence electrons: electrons in the outermost energy level, these are the electrons with
the highest energy.
Elements in the same family have similar properties because they have the same
number of valence electrons
Valence electrons determine how elements chemically bond.