Periodic Groups and Trends
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Transcript of Periodic Groups and Trends
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Periodic Groups and Trends
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Periodic Table• Periodicity: regular variations (or patterns) of
properties with increasing atomic weight. Both chemical and physical properties vary in a periodic (repeating pattern).
• Group: vertical column of elements (“family”)
• Period: horizontal row of elements
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Activity: get out your black and white copy of the periodic table.
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On one side, color and label the metals, nonmetals, and metalloids.
Another name for “metalloid” is “semi-metal”.
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Transition metals
alka
li m
etal
sal
kalin
e ea
rth m
etal
s
halo
gens
nobl
e ga
ses
lanthanidesactinides
Color and label the groups/families of elements on the other side of your paper. Remember to create a legend.
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PERIODIC GROUPS
• alkali metals• alkaline earth metals• transition metals• halogens• noble gases• lanthanides• actinides
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Alkali Metals
• Group 1 on periodic table• Very reactive• Soft solids• Readily combine with halogens• Tendency to lose one electron
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Alkaline Earth Metals
• Group 2 on periodic table• Abundant metals in the earth• Not as reactive as alkali metals• Higher density and melting point than
alkali metals
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Transition Metals
• Groups 3-12 on periodic table• Important for living organisms
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Halogens
• Group 17 on periodic table• “Salt former” – combines with groups 1
and 2 to form salts (ionic bonds)
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Noble Gases
• Group 18 on periodic table• Relatively inert, or nonreactive• Gases at room temperature
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Lanthanides
• Part of the “inner transition metals”• Soft silvery metals• Tarnish readily in air• React slowly with water
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Actinides
• Radioactive elements• Part of the “inner transition metals”
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PERIODIC PROPERTIES
• Atomic radii• Ionization energy• Ionic radii• Electronegativity
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Atomic Radii
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Atomic Radii
• Trend: increases down a group
• WHY???– The atomic radius gets bigger because
electrons are added to energy levels farther away from the nucleus.
– Plus, the inner electrons shield the outer electrons from the positive charge (“pull”) of the nucleus; known as the SHIELDING EFFECT
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Atomic Radii
• Trend: decreases across a period
• WHY???– As the # of protons in the nucleus
increases, the positive charge increases and as a result, the “pull” on the electrons increases.
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Ionization Energy• Definition: energy required to remove outer electrons
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Ionization Energy• Definition: energy required to remove outer electrons
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Ionization Energy
• Trend: decreases down a group
• WHY???– Electrons are in higher energy levels as you
move down a group; they are further away from the positive “pull” of the nucleus and therefore easier to remove.
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Ionization Energy
• Trend: increases across a period
• WHY???– The increasing charge in the nucleus as
you move across a period exerts greater “pull” on the electrons; it requires more energy to remove an electron.
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Ionic Radii
• Cations are always smaller than the metal atoms from which they are formed. (fewer electrons)
• Anions are always larger than the nonmetal atoms from which they are formed. (more electrons)
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Electronegativity
• Definition: the tendency of an atom to attract electrons to itself when chemically combined with another element
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Electronegativity
• Trend: decreases down a group
• WHY???– Although the nuclear charge is increasing,
the larger size produced by the added energy levels means the electrons are farther away from the nucleus; decreased attraction, so decreased electronegativity; plus, shielding effect
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• Trend: increases across a period (noble gases excluded!)
• WHY???– Nuclear charge is increasing, atomic radius is
decreasing; attractive force that the nucleus can exert on another electron increases.
Electronegativity
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Summing Up Periodic Trends