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)

• Based on the number of protons in the nucleus.
• Example Carbon vs. Nitrogen

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The Nuclear Charge (Z)
Carbon
Nitrogen
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The Nuclear Charge (Z)

• The greater the number of protons in the nucleus
  the greater the effective nuclear charge.

Nitrogen
Carbon
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Conclusion Nitrogen is a smaller atom than
carbon because nitrogen has 7 protons to pull in
its electrons whereas carbon only has 6.
Nitrogen
Carbon
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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.
He
Ne
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Conclusion Neon is larger than helium because
it has an increased shielding effect from having
two energy levels whereas helium only has one
energy level.
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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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