Chapter 5 Organizing The
Elements
OBJECTIVES
• Describe how Mendeleev arranged the elements in his
table
• Explain how the predictions Mendeleev made and the
discovery of new elements demonstrated the usefulness of
his periodic table
• Describe the arrangement of elements in the modern
periodic table
• Explain how the atomic mass of an element is determined
and how atomic mass units are defined
• Identify general properties of metals, nonmetals, and
metalloids
• Describe how properties of elements change across a
period in the periodic table
• Relate the number of valence electrons to groups in the
periodic table and to properties of elements in those groups
• Predict the reactivity of some elements based on their
locations within a group
• Identify some properties of common A group elements
• In 1750 scientists had identified only 17
elements most of these were metals
• As the number of identified elements grew
so did the need for organization
• In 1789 Antoine Lavoisier grouped
elements according to categories called
metals, non-metals, gases and earths
• In 1860 Mendeleev (Russian) needed to describe
the now known 63 elements to his students
• On cards, he listed the name, mass and properties
of the 63 elements
• He arranged them in order of increasing atomic
mass. He was able to break the elements into
rows (see pg 127 Fig. 3 and columns based on the
properties of the elements
• Columns increased from TOP to BOTTOM
• He knew that not all elements were
discovered yet so he left room for them
• Properties of elements are related to its
location in the table
• Review questions 1-5 pg. 129
5.2 Modern Periodic law
• In the modern periodic table, elements are arranged by
increasing ATOMIC NUMBER (number of protons)
• PERIODS
• Each row in the periodic table is a period
• Ex. Period 1 has 2 elements period 2 and 3 have 8
elements
• The number of elements in each period varies because of
the available orbitals increase from energy level to energy
level
• In other words---------the first energy level has
only 1 orbital so, the 1 electron in a H atom and
the 2 electrons in a He atom can fit in this orbital
• But Li contains 3 electrons---------so 2 can fit in
the 1st orbital and the other electron has to go in
the 2nd orbital(or energy level) this is why Li is
the first element in Period 2
• Na (sodium) the first element in period 3 has one
electron in its 3rd orbital or energy level
• K (potassium), the first element in Period 4 has
one electron in its 4th orbital
• This pattern applies to all elements in the first
column on the table
• GROUPS (FAMILIES)
• Each COLUMN is called a group or family
• The elements within a group have similar properties
(electron configurations)
• The electron configuration determines the chemical
properties
• THE PATTERN OF REPEATING CHEMICAL
PROPERTIES IS CALLED PERIODIC LAW
• REFER TO FIG. 7 PGS 132-133
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Atomic Mass
Copy Fig. 8 into your notebook
There are 4 pieces of information for each element
Name of the element, its symbol, its atomic
number, and its atomic mass(the number of
isotopes and their mass in nature)
• Atoms of 2 isotopes have different atomic
masses(isotopes have different # of neutrons than
protons) they are usually equal
Classes of Elements
• Solids, liquids, gases based on their state at room
temperature
• Symbols solids (black) liquid (purple) gas (red)
• Elements are divided into those that occur
naturally and those that do not
• Ex. Elements with an atomic number of 93 or
above DO NOT OCCUR NATURALLY
• 1-92 occur naturally
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Third classification is based on general properties
Metals—located on left (blue)
Non-metals located on right (yellow)
Metalloids located in the middle (green)
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METALS
Majority of elements are metals
Represented by blue boxes
Good conductors of heat
Electric current
Solid at room temperature (except mercury)
Most are malleable
Many are ductile (able to be drawn into thin wire)
• Groups 3 through 12 are referred to as transition
metals
• These transition metals form a bridge between the
elements on the left and right
• One property of these metals is their ability to
form compounds with distinct colors
• Ex. Tinted glass
• They are among the 1st elements discovered
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NONMETALS
Represented by yellow boxes
Have properties opposite to those of metals
Poor conductivity of heat and electric
Low boiling points
Many are gases at room temperature
Are brittle (will shatter or crumble)
• METALLOIDS
• Represented by green boxes
• Properties of these elements fall somewhere
between metals and nonmetals
• Their ability to conduct heat or electric depends on
their temperature
Variation across a Period
• Changes in the properties of elements change in a similar
way when you move from left to right (except for period 1)
• From left to right, elements become less metallic and more
nonmetallic
• Most reactant elements or on the left side of the table
• Most reactive nonmetals are on the right side (group 17)
• Copy fig. 13 into your notebooks
• Complete questions 1-5 and 7
• Valence electrons
• An electron that is in the highest occupied energy
level of an atom
• Valence electrons play a key role in chemical
reactions
• The properties of elements vary because the
number of valence electrons increases from left to
right
• Remember that elements in a group have
similar properties because they have the
same number of valence electrons
• Ex. Hydrogen and Lithium have I valence
electron
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Alkali metals elements in group 1A
1 valence electron
Highly reactive
Ex. Sodium chloride (table salt)
Group 1A Li, Na, K, Rb, Cs, Fr
Their reactivity increases from TOP TO
BOTTOM
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Alkaline Earth metals
Group 2A
Contain 2 valence electrons
Harder than metals in group 1A
Differences in reactions with water
Calcium and magnesium are essential to biological
functions
• Magnesium
• Key role in photosynthesis
• Mixture of magnesium and other metals can be as
strong as steel but much lighter
• Calcium
• Keeps bones and teeth strong, toothpastes may
contain calcium to polish teeth
• Plaster casts contain calcium sulfate
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The Boron Family
Group 3A
Contain 3 valence electrons
Aluminum(metal) most abundant metal in the
earth’s crust
• Boron(metalloid)
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The Carbon Family
Group 4A
4 valence electrons
Contains 1 nonmetal(carbon)
2 metalloids(silicon, germanium)
2 metals(tin, lead)
Life on earth would not exist without carbon, most
compounds in your body contain carbon
• Silicon is the 2nd most abundant element in the crust
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The Nitrogen family
Group 5A
Contain 5 valence electrons
Contain 2 nonmetals(arsenic, antimony)
1 metal(bismuth)
1 nonmetal gas (nitrogen)
1 solid nonmetal(phosphorus)
In this group phosphorus and nitrogen are most important
Contained in fertilizers and compounds in your body to
release energy
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The Oxygen family
Group 6A
Contain 6 valence electrons
3 nonmetals (oxygen, sulfur, selenium)
2 metalloids (tellurium, polonium)
Oxygen is the most abundant element in the earth’s crust
Can be stored as a liquid, under pressure
Ozone is another form of oxygen ground level is an eye
irritant, in the atmosphere absorbs radiation
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The Halogens
Group 7A
7 valence electrons
Highly reactive nonmetals
2 gases (fluorine, chlorine)
1 liquid (bromine)
1 solid (iodine)
All react easily with most metals
• Fluorine compound used to prevent tooth decay,
non-stick coatings
• Chlorine is in bleach, and used to kill bacteria in
drinking water and pools (bromine for hot tubs)
• Your body needs iodine to keep your thyroid gland
working properly
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The Noble Gases
Group 8A
8 valence electrons (except helium) (2)
This means these elements have a full outer shell
This group does not react with any other elements
Questions 1-10 page 145
Internet activity—see if you can find the 25 essential
elements to the human body and 3 elements that should be
avoided completely