Periodic Trends

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Chapter 10

• Periodic Trends
• Density
• Atomic and Ionic Radii

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Density
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Density

• Iridium (Z 77) has the highest density.
• Why not Meitnerium (Z 109?)
• We can predict that an element is more dense if
  it is closer to Iridium.

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Density
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Effective Nuclear Charge (Zeff)

• The effective nuclear charge (Zeff) of an atom is
  basically how well it is able to hold on to its
  most loosely held electron.

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Atomic radius (radii)

• The atomic radius is essentially the size of an
  atom.
• The largest atom is Francium (Z 87).

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Atomic Radius
Xylophone monkey
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Rank the atoms from smallest to largest

• Na, K, O, N
• O lt N lt Na lt K

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Atomic Radius and Effective Nuclear Charge

• The atomic radius decreases as effective nuclear
  charge increases.

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Effective Nuclear Charge (Zeff)

• The effective nuclear charge of an atom is
  primarily determined by
• The nuclear charge
• The shielding effect

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The Nuclear Charge (Z)

• Example Carbon vs. Nitrogen
• Which atom would you predict to be smaller?

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The Nuclear Charge (Z)
Carbon
Nitrogen
Both atoms are in the 2nd row (period) of the
periodic table. What does this tell us?
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Conclusion Nitrogen has a greater effective
nuclear charge than carbon because nitrogen has 7
protons to pull in its two energy levels of
whereas carbon only has 6 protons holding its
two energy levels. Therefore nitrogen atoms are
smaller than carbon atoms.
Carbon
Nitrogen
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The Nuclear Charge (Z)

• The size of atoms in the same period (row) is
  determined by the nuclear charge (number of
  protons in the nucleus).

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Nuclear charge explains why atoms get smaller
across a period
Atomic Radius
Xylophone monkey
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Shielding Effect.

• The shielding effect is when electrons between
  the nucleus and the outermost electrons in an
  atom shield or lessen the hold of the nucleus on
  the outermost electrons.

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Shielding Effect.Why is He smaller than Ne?
He
Ne
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Conclusion Helium has a greater effective
nuclear charge than neon because helium has a
lower shielding effect from having only one
energy level whereas helium two.
He
Ne
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Shielding Effect explains why atoms get larger
down a group
Atomic Radius
Xylophone monkey
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Chemical Reactivity
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Chemical Reactivity
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Chemical Reactivity

• Metals tend to lose electrons when reacting.
• Large metal atoms are more reactive.
• Nonmetals tend to gain electrons when reacting.
• Small nonmetal atoms are more reactive.

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Chemical Reactivity

• Metals increase in reactivity left and down.
• Nonmetals become more reactive up and to the
  right.
• Most reactive metal is?
• Most reactive nonmetal is?

Fr
F
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Francium

• Francium is the least stable naturally occurring
  element with a half-life of only 22 minutes.
• It has been calculated that there is at most 30 g
  of francium in the Earth's crust at any time.

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Ionic Radius

• Ionic Radius is the size of an ion.

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Size Change in Ion Formation
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Rules for Ionic Radius

• Anions (negative ions) are always larger than
  cations (positive ions).
• Ionic Radius goes by the same rules as atomic
  radius (ions get larger as we move down and to
  the left).
• However it is necessary to treat anions and
  cations separately. (Anions are bigger).

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Rank the ions from smallest to largest

• K, N3-, Na, O2-
• Na lt K lt O2- lt N3-

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Homework

• Worksheet Density, Atomic and Ionic Radii (due
  tomorrow).
• Lab Summary Reactivity and the Periodic Table
  (due Monday).
• Study Guide Chapter 10 (due Tuesday).