Transcript Periodic Trends

Periodic Trends
Periodic Patterns
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Ion formation: Loss (oxidation) or gain (reduction) of electrons
Periodic Trends
• Trends in atomic radius, ionization energy, &
electronegativity are determined by:
• The number of energy levels present.
• The attraction between the positive nucleus and the
outer shell electrons.
• Interfering “shielding” by electrons on inner shells.
• How close an atom is to completing the stable octet
of outer “valence” electrons.
Atomic Radius (1 of 3)
• Alkali metals are the largest atoms.
• Noble gases are the smallest atoms.
Atomic Radius (2 of 3)
Atomic radius
trends:
1) Atomic radius
increases down
a group or
column.
2) Atomic radius
decreases
across a period
or row.
Atomic Radius (3 of 3)
How do we explain the trends?
1. Atomic radius increases down a group:
•
•
Each row adds an energy level.
Interior electrons interfere with attraction of
valence electrons toward the nucleus “shielding
effect”
2. Atomic radius decreases across a row even
while the atomic number increases:
•
While in the same energy level, the nucleus
becomes more positive & attractive.
Ionization Energy (1 of 4)
• Ionization energy is
the energy required
to remove a negative
electron and leave an
atom with a positive
charge – as an ion.
• Occurs in solar cells,
geiger counters &
smoke detectors with
Amerecium 241
Ionization Energy (2 of 4)
• Alkali metals lose their electrons most easily.
• Noble gases hold their electrons most tightly.
Ionization Energy (3 of 4)
• Removing an
electron
becomes more
difficult across a
row.
• Removing
electrons
becomes easier
down a column.
Ionization Energy (4 of 4)
• Removing electrons is more difficult across a row as
the nuclear attractions become stronger.
• Removing electrons is easier down a column as each
additional energy level increases the distance from
the nucleus and weakens the nuclear attraction.
• Repulsive shielding by interior electrons also
decreases the attraction for each added level.
Electronegativity (1 of 3)
• Electronegativity is
the ability of
an atom to
attract
electrons
that are
shared in a
covalent
bond.
Electronegativity (2 of 3)
• What are the trends in electronegativity?
Electronegativity (3 of 3)
• Electronegativity
increases up & to
the right.
• This trend
corresponds to
stronger attractions
to the nucleus.
• Less shielding effect
strengthens
attractions to the
nucleus in upper
rows.
Periodic Patterns Quiz
Atomic Radius Question – What is the size
surprise? Why does it occur?
Ionization Energy – Why are the lowest
ionization energies in the bottom left?
Electronegativity – Arrange each set of atoms in
order from least to greatest electronegativity:
Mg, Ba, Sr; Cl, F, I; Fe, K, Br
Periodic Patterns of Reactivity
• Choose an element from the periodic table.
• Predict how you think it will react with air,
water, acids or bases.
• Observe the laserdisc video.
• Record the reactivity on a 1R-10R scale.
• Examine no more than 3 per group.
• Identify patterns of reactivity.