how did mendeleev arrange the elements in his periodic table ......2015/02/06 · the periodic...
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The Periodic Table Section 1
Recognizing a Pattern
〉How did Mendeleev arrange the elements in his periodic table?
〉In his periodic table, Mendeleev arranged elements in rows by increasing atomic mass.
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The Periodic Table Section 1
Recognizing a Pattern, continued
• Mendeleev was able to predict new elements.
– Mendeleev left spaces in his
table to make the pattern fit.
– He used the spaces to
successfully predict the
existence and properties of
elements not yet discovered.
• A few elements did not fit the pattern.
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The Periodic Table Section 1
Changing the Arrangement
〉How are elements arranged in the modern
periodic table?
〉The modern periodic table organizes elements
by atomic number. When the elements are
arranged in this way, elements that have similar
properties appear at regular intervals.
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The Periodic Table Section 1
Changing the Arrangement, continued
• As scientists learned more about the structure of the
atom, they improved Mendeleev’s table.
• Arranging the table by atomic number (number of
protons) rather than by atomic mass fixed the
discrepancies in Mendeleev’s table.
• periodic law: the law that states that the repeating
chemical and physical properties of elements change
periodically with the atomic numbers of the elements
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The Periodic Table Section 1
The Periodic Table of the Elements
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The Periodic Table Section 1
Changing the Arrangement, continued
• Elements become less metallic across each period.
– period: a horizontal row of elements in the periodic
table
• Elements in a group have similar properties.
– group: a vertical column of elements in the periodic
table; elements in a group share chemical properties
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The Periodic Table Section 2
The Role of Electrons
〉Why do elements within a group of the periodic table have similar chemical properties?
〉The periodic trends in the periodic table are the result of electron arrangement.
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The Periodic Table Section 2
The Role of Electrons, continued
• Valence electrons account for similar properties.
• An element’s location in the periodic table is related to electron arrangement.
– Example: Lithium and sodium, in Group 1, each have one valence electron.
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The Periodic Table Section 2
Ion Formation
〉What happens to an atom that gains or loses
electrons?
〉If an atom gains or loses electrons, it no longer
has an equal number of electrons and protons.
Because the charges do not cancel completely,
the atom has a net electric charge.
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The Periodic Table Section 2
Ion Formation, continued
• Group 1 elements
form positive ions.
– The single valence
electron is easily
removed.
• Group 17 elements
form negative ions.
– The addition of one
valence electron fills
the outer energy level.
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The Periodic Table Section 2
How Are Elements Classified?
〉What are the three main categories of
elements?
〉All elements are either metals, nonmetals, or
semiconductors.
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The Periodic Table Section 2
How Are Elements Classified?,
continued
• Elements in each category have similar properties.
– metal: an element that is shiny and that conducts
heat and electricity well
– nonmetal: an element that conducts heat and
electricity poorly
– semiconductor (or metalloid): an element or
compound that conducts electric current better than
an insulator does but not as well as a conductor does
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The Periodic Table Section 2
How Are Elements Classified?,
continued
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The Periodic Table Section 3
Classifying Elements Further
〉What does each element family have in common?
〉In general, the elements in a family have the same number of valence electrons.
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The Periodic Table Section 3
Metals
〉What are the families of metals?
〉Families of metals include the alkali metals, the
alkaline-earth metals, and the transition metals.
– alkali metal: one of the elements of Group 1 of the periodic table
– alkaline-earth metal: one of the elements of Group 2 of the periodic table
– transition metal: one of the metals that can use the inner shell before using the outer shell to bond
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The Periodic Table Section 3
Metals, continued
• The alkali metals are very reactive. – Alkali metals are in Group
1, on the left edge of the periodic table.
– They are reactive because they have one valence electron that is easily removed.
– They are soft and shiny,
and many have similar
melting points, boiling
points, and densities.
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The Periodic Table Section 3
Metals, continued
• Alkaline-earth metals form compounds that are found in limestone and in the human body.
– Alkaline-earth metals are in Group 2.
– Alkaline-earth metals are less reactive than alkali metals, but still react to form positive ions.
– In general, alkaline-earth metals are harder, denser, stronger, and have higher melting points than alkali metals.
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The Periodic Table Section 3
Metals, continued
• Transition metals are in the middle of the periodic table.
– With the exception of mercury, transition metals are
harder, more dense,
and have higher
melting points than
alkali metals and
alkaline-earth metals.
– They are also less
reactive, but they can
form positive ions.
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The Periodic Table Section 3
Nonmetals
〉What are some of the families of nonmetals?
〉Families of nonmetals include the noble gases
and the halogens.
– noble gas: one of the elements of Group 18 of the
periodic table
– halogen: one of the elements of Group 17 of the
periodic table
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The Periodic Table Section 3
Nonmetals, continued
• The noble gases are relatively inert.
– The noble gases are in Group 18.
– They exist as single atoms instead of as molecules.
– They are inert, or unreactive, because their s and p orbitals are filled. In general, they do not form ions or compounds.
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The Periodic Table Section 3
Nonmetals, continued
• The halogens combine easily with metals to form salts.
– The halogens are in
Group 17.
– With the addition of a
single electron,
halogens become
stable.
– They combine easily
with metals (especially
alkali metals) to form
salts.
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The Periodic Table Section 3
Nonmetals, continued
• Nonmetals and their compounds are plentiful on Earth.
– Six other nonmetals
are on the right side of
the periodic table.
• Carbon can form many
compounds.
– There are millions of
carbon-containing
compounds.
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The Periodic Table Section 3
Semiconductors
〉What are semiconductors?
〉As their name suggests,
semiconductors are able to
conduct heat and electricity
under certain conditions.
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