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The Periodic Table
Periods, groups, and trends
The Bohr Model
• After Rutherford’s model of the atom, Neils
Bohr created our modern atomic model
• He suggested that the electrons of an element
are arranged in energy levels or “energy
shells”
• Using this model helps us understand the
periodic table of elements
What is The Periodic Table of
Elements?
• An arrangement of the elements
Periodic Law
• “When the elements are arranged according
to their atomic numbers, elements with
similar properties appear at regular intervals”
• When elements are arranged by their atomic
numbers, groups of elements begin to have
similar characteristics
Organization of the Periodic Table
• Elements in each column of the periodic table
have the same number of electrons in their
outer shell
– Called “valence electrons”
• Elements with the same number of valence
electrons react in similar ways
Periods
• A horizontal row on the periodic table of
elements is called a period
Groups
• A vertical column of the periodic table is called
a group
• Elements in a group share similar chemical
properties
Main Group Elements
• Elements in groups 1,2, and 13-18 are known as
main group elements
• Electron configurations of each element are
regular and consistent
• Main group elements include:
–
–
–
–
Alkali Metals
Alkaline Earth Metals
Halogens
Noble Gases
Alkali Metals – Group 1
Alkali Metals – Group 1
• They are metals that react with water
– They are very reactive
• Never found in nature as “pure elements” but
are found as compounds
• Lithium, Sodium, Potassium, Rubidium,
Cesium, and Francium
Alkaline Earth Metals – Group 2
Alkaline Earth Metals – Group 2
• Slightly less reactive than Alkali Metals
• Have 2 valence electrons
Halogens – Group 17
Halogens– Group 17
• The most reactive group of the non metal
elements
• They have 8 valence electrons
• React with most metals to produce salts
– Sodium and Chlorine – Table Salt
Noble Gases – Group 18
Noble Gases – Group 18
• Group 18 elements are called Noble Gases
• Have a very low reactivity
Hydrogen
• The most common element in the universe
• It only has one proton and one electron so it is
unlike any other element
• Reacts with many other elements
Transition Metals
• These occupy the center of the periodic table
Transition Metals cont.
• Extremely unreactive
• Some almost never form compounds with
other elements
Metals
• All Metals are excellent conductors of
electricity
– Most often distinguishes metals from non-metals
• Can be brittle or malleable
Metalloids
• Found on the table between metals and non
metals
Metalloids
• All metalloids are solids at room temperature
• Have some characteristics of metals and have
some characteristics of non-metals
Non-Metals
• Many non-metals are gases at room
temperature
• Poor conductor of heat and electricity
• Found on the right side of the periodic table
Periodic Trends
• The arrangement of the periodic table reveals
trends in the properties of the elements
– A trend is a predictable change or characteristic
• Understanding a trend among elements in a
group or period enables you to make
predictions about their behavior
Ionization Energy
• Ionization energy is the energy required to
remove an electron from an atom
Ionization Energy Cont.
• Ionization energy decreases as you move
down a group
Ionization Energy cont.
• Ionization energy increases as you move from
left to right across a period
Melting Point
• Metals generally posses a high melting point
• Most nonmetals possess low melting points
Electronegativity
• Refers to how strongly each atom attracts
other electrons
• An atom with higher electronegativity will pull
on the electrons more strongly than another
atom will
• Electronegativity decreases as you move down
a group
• Electronegativity increases from left to right
across a period