Transcript Period Trend

Periodic Table Periods
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Atoms in a period have the same number
of energy levels.
Periodic Table Groups
Many groups have special names that
describe their characteristics.
 Atoms in a group have same number of
valence electrons so they behave
similarly.
 Roman numerals represent the
number of valence electrons.
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Terms to Know
Cations refer to the elements that lose
electrons and form a positive ion.
 Anions refer to the elements that gain
electrons and form a negative ion.
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Alkali Metals
All form +1 cations
 Very reactive with water
 Highly reactive in general
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Alkaline Earth Metals
All form +2 Cations
 Somewhat reactive with water
 Highly reactive with acids.
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Halogens
All form -1 Anions
 Aggressive Oxidizers
 Used in Halogen bulbs.
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Noble Gases
Non-reactive
 Fulfilled Octet Rule—have 8 valence
electrons in the outer most energy level
and considered stable.
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Other Groups
Group 13 (IIIA) – Boron Family
 Form +3 Cations
 Group 14 (IVA) – Carbon Family
 Form + 4 Cations or Anions
 Group 15 (VA) – Nitrogen Group
 Form -3 Anions
 Group 16 (VIA) – Oxygen Family
 Form -2 Anions
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Periodicity
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When elements are arranged in order of
increasing atomic number, there is a periodic
repetition of their physical and chemical
properties.
An important consequence is that the elements
with similar chemical and physical properties
end up in the same column.
Trends on the periodic table govern how
elements behave chemically.
All elements are unique, but follow these
trends….generally.
Atomic Size/Atomic Radius
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Atomic radius is ½ the distance between the
nuclei of identical atoms that are bonded together.
Group Trend – size INCREASES as you move
down (added energy levels; electrons farther from
nucleus).
Period Trend – size DECREASES as you move
left to right (more protons and electrons pulling
harder on one another).
 Due to increasing energy levels and shielding
by inner electrons. Inner electrons shield the
outermost electrons from the nucleus.
Atomic Size Cont.
Examples
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Which atom has the larger radius?
Be
or Ba
Ba
Ca
or Br
Ca
Ionic Size/Ionic Radius
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Ionic Radius is the relative size of the most
common ion of an atom.
Group Trend – INCREASE top to bottom due
to shielding.
 Cations are always smaller than their neutral
atom
 Loss of electrons increase attraction
 Anions are always bigger than their neutral
atom.
 Gain of electrons decrease attraction
Period Trend – DECREASE left to right.
Electronegativity
Electronegativity is a measure of the ability
of an atom in a chemical compound to
attract electrons when they are chemically
combined with atoms of another element.
 Group Trend – DECREASE as you move
down due to increasing number of energy
levels.
 Period Trend – INCREASE from left to right
right due to switch from cat ions to anions.
 Fluorine has an electronegativity of 4.0,
everything below and to the left is lower.
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Electronegativity
Electronegativity
Ionization Energy
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Ionization Energy is the energy required to
overcome the attraction of the protons and
remove one electron from a neutral atom of an
element .
The energy required to remove the 1st outermost
electron is call the 1st ionization energy. And the
energy for the 2nd outermost electron to be
removed is called 2nd ionization energy.
Atoms may have 2nd or 3rd ionization energies
depending on number of valence electrons and
adherence to octet rule.
Ionization Energy
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Group Trend – ionization energy DECREASES
as you move down (electrons further from the
pull of the nucleus are easier to remove).
Period Trend – ionization energy INCREASES
as you move left to right (greater attraction of
the nucleus for electrons).
Ionization Energy Cont.
Examples
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Which atom has the higher 1st I.E.?
N
or Bi
N
Ba
or Ne
Ne
Summary of Periodic Trends