Transcript Trend - FraserChem111

Periodic Trends
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Types of Periodic Trends
4 Periodic Trends
1.Atomic Radii (AR)
2.Ionization Energy (IE)
3.Ionic Radii (IR)
4.Electronegativity (EN)
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Trends in Atomic Size
The atomic radius is one half of the distance
between the nuclei of two atoms of the same
element when the atoms are joined.
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Trends in Atomic Size
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Periodic Trends
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Trends in Atomic Size
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Atomic Radii (AR) Periodic Trend
Down a Group:
Trend: The atomic radius increases as the
atomic # increases within a group
Reason: The number of protons in the nucleus
(NUCLEAR CHARGE) increases, increasing the
positive charge drawing electrons close to the
nucleus, but the number of occupied orbitals
also increases the SHIELDING of electrons from
the effect of the nuclear charge. (SHIELDING
EFFECT)
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Across a Period:
Trend: Atomic size decreases across a
period from left to right.
Reason: Electrons are added to the same
energy level so shielding is constant for
all elements in a period. The increasing
nuclear charge pulls the electrons in
closer to the nucleus.
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Ions
An ion is an atom or group of atoms that
has a positive or negative charge.
• A cation is an ion with a positive charge.
• An anion is an ion with a negative charge.
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Ions
Metals elements lose valence electrons to form
cation ions. Cation radii (IR) are always smaller
than atomic radii (AR) [i.e. IR < AR]
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Ions
Non-metal elements gain valence electrons to
form anion ions. Anion radii (IR) are always
larger than atomic radii (AR) [i.e. IR > AR]
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Trends in Ionic Size
Relative Sizes of Some Atoms and Ions
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Trends in Ionic Size
Size generally increases
Trends in Ionic Size
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Ionic Radii Periodic Trend
Periodic Trend for Ionic Radii (IR)
Down a Group:
Trend: Size of the Ion generally increases.
Reason: Atomic Number increases. Number of
energy levels increases.
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Across a Period: Metals large  small, then Non-metal
large  small (Caution: Are not looking at same charge ion
when across period)
Periodic Trends
Metals: IR vs. AR :Ionic radii is smaller than atomic radii.
Cation size decreases.
Reason: When an atom loses an electron, the attraction
between the remaining electrons and the nucleus
increases and electrons are drawn closer to the nucleus.
Also, metals tend to lose their outermost electrons- one
fewer occupied energy level.
Non-metals: IR vs. AR : The trend is opposite Ionic radii
is larger than atomic radii. Anion size decreases
Reason: The total number of electrons will be the same but
the nuclear charge increases so the attraction from the
protons increases, decreasing overall size.
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Trends in Ionization Energy
Ionization Energy (IE) - The energy required to
remove the first valence electron from an atom
(atom is in the gas phase).
• What is holding the valence electron to the
atom?
• Valence electron tightly held or loosely?
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Trends in Ionization Energy
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Trends in Ionization Energy
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Periodic Trends
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Trends in Ionization Energy
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Ionization Energy (IE) Periodic Trend
Periodic Trend for Ionization Energy (IE)
Down a Group:
Trend: Decreases as atomic # increases.
Reason: Nuclear charge has a decreasing effect on
electrons as they move further and further away from
the nucleus. Shielding effect is greater as you move
down a group.
Across a Period: Trend: Increases from left to right.
Reason: The nuclear charge increases, the shielding
effect remains the same, electrons are more attracted to
the nucleus as you move across the period.
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Ionization Energy (IE) Periodic Trends
Two Exception to 1st Ionization Energy (IE)
(Across the Period):
1. Be  B
Trend: Drop in energy required.
Reason: Easier to take a “p” than an “s” electron
because it is further away from the nucleus.
2. N  O
Trend: Drop in energy required.
Reason: p4 electron is the first pair in the p sublevel.
Repulsion created, lowers the amount of energy
required to remove the electron.
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Trends in Electronegativity
•Trends in Electronegativity
Electronegativity is the ability of an atom, in a chemical
bond, to attract the shared valence electrons to itself.
(i.e. the shared valence electrons are physically closer to
the higher EN value atom than the other atom in the
chemical bond).
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Trends in Electronegativity
Trends in Electronegativity
In general, electronegativity values
decrease from top to bottom within a
group. For representative elements, the
values tend to increase from left to right
across a period.
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Trends in Electronegativity
Representative Elements in Groups 1A through 7A
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Periodic Trends
Summary of Trends
Increases
Decreases
Constant
Increases Decreases
Size
Electronegativity
Ionic
Atomic
Nuclear
Shielding
Ionization
of
size
cations
Size
anions
Charge
energy
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