periodic groups and trends. periodic table periodicity: regular variations (or patterns) of...
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Periodic Groups and Trends
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
Activity: get out your black and white copy of the periodic table.
On one side, color and label the metals, nonmetals, and metalloids.
Another name for “metalloid” is “semi-metal”.
Transition metals
alk
ali
meta
ls
alk
alin
e e
art
h m
eta
ls
halo
gen
s
nob
le
gase
s
lanthanides
actinides
Color and label the groups/families of elements on the other side of your paper. Remember to create a legend.
PERIODIC GROUPS
• alkali metals
• alkaline earth metals
• transition metals
• halogens
• noble gases
• lanthanides
• actinides
Alkali Metals
• Group 1 on periodic table
• Very reactive
• Soft solids
• Readily combine with halogens (ex. NaCl)
• Tendency to lose one electron (to become an ion)
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
Transition Metals
• Groups 3-12 on periodic table Important for living organisms (think vitamins: multivitamins (they have iron, zinc, chromium, etc.)
Halogens
• Group 7A on periodic table
(***or GROUP 17)
• “Salt former” – combines with groups 1 and 2 to form salts (ionic bonds)
Noble Gases
• Group 8 on periodic table
(** or GROUP 18)
• Relatively inert, or nonreactive
• Gases at room temperature
Lanthanides
• Part of the “inner transition metals”
• Soft silvery metals
• Tarnish readily in air
• React slowly with water
Actinides
• Radioactive elements
• Part of the “inner transition metals”
PERIODIC TRENDS
• Atomic radii
• Ionization energy
• Ionic radii
• Electronegativity
Atomic Radii
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
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.
Ionization Energy• Definition: energy required to remove outer electrons
Ionization Energy• Definition: energy required to remove outer electrons
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.
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.
Ionic Radii
• Cations are always smaller than the metal atoms from which they are formed. (fewer electrons because metals LOSE electrons)
• Anions are always larger than the nonmetal atoms from which they are formed. (more electrons because nonmetals GAIN electrons)
Electronegativity
• Definition: the tendency of an atom to attract electrons to itself when chemically combined with another element
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
• 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
Summing Up Periodic Summing Up Periodic TrendsTrends