Download The atomic radius

Chapter 10
Periodic Trends
Density
Atomic and Ionic Radii
Density
• Iridium (Z = 77) has the highest density.
• We can predict that an element is more
dense if it is closer to Iridium.
Density
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.
Atomic radius (radii)
• The atomic radius is essentially the size
of an atom.
Atomic radius (radii)
• The atomic radius is essentially the size
of an atom.
• The largest atom is Francium (Z = 87).
Atomic radius (radii)
• The atomic radius is essentially the size
of an atom.
• The largest atom is Francium (Z = 87).
• We can predict that an atom is larger if it is
closer to Francium.
Atomic Radius
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Atomic Radius and Effective
Nuclear Charge
• The atomic radius decreases as effective
nuclear charge increases.
Effective Nuclear Charge (Zeff)
•
The effective nuclear charge of an atom
is primarily determined by:
1. The nuclear charge
2. The shielding effect
The Nuclear Charge (Z)
• Based on the number of protons in the
nucleus.
– Example: Carbon vs. Nitrogen
The Nuclear Charge (Z)
The Nuclear Charge (Z)
• The greater the number of protons in the nucleus
the greater the effective nuclear charge.
Conclusion: Nitrogen is a smaller atom than carbon because
nitrogen has 7 protons to pull in its electrons whereas carbon
only has 6.
Nuclear charge explains why atoms get smaller across a period
Atomic Radius
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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.
Shielding Effect.
He
Ne
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
Rank the atoms from smallest to largest
• Na, K, O, N
Chemical Reactivity
• Metals tend to lose electrons when reacting
• Nonmetals tend to gain electrons when reacting
• Effective nuclear charge allows us to use the
periodic table to predict reactivity.
Chemical Reactivity
• Metals increase
in reactivity left
and down.
• Nonmetals
become more
reactive up and
to the right.
• Most reactive
metal is? Fr
• Most reactive
nonmetal is? F
Shielding Effect explains why atoms get larger down a group
Atomic Radius
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Ionic Radius
• Ionic Radius is the size of an ion.
Size Change in Ion Formation
Rules for Ionic Radius
• Ionic Radius goes by the same rules as
atomic radius however it is necessary to
treat anions and cations seperately.
• Anions are “always” larger than cations.
Rank the ions from smallest to largest
• K+, N3-, Na+, O2-
Homework
• Worksheet: Density, Atomic and Ionic Radii