Transcript Regents Unit 8 Ionization Energy and the Periodic Table

Trends & the Periodic Table
Ionization Energy,
Electronegativity, & Metallic
Reactivity
Trends
• More than 20 properties change in a
predictable way based on location of
element in P.T.
• Include: density, melting point, atomic
radius, ionization energy, electronegativity
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Size  as you go  and size  as you go 
Source: Conceptual Chemistry by John Suchocki
What’s the trend for effective
nuclear charge?
• Effective Nuclear Charge =
Atomic # - Inner Shell Electrons.
• Increases as you go across a row.
• Stays constant as you go down a column.
Ionization Energy
• Amount of energy required to remove an
electron from a gas-phase atom.
• First ionization energy or ionization energy
= energy required to remove most loosely
held valence electron.
• Na(g) + energy  Na+1(g) + 1e• (This is an endothermic process!)
Trends in ionization energy
• What do you think happens to the
ionization energy as you go down a
column of the periodic table? Li vs. Cs?
• As you go across a row? Li vs. F?
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
Valence electrons in both atoms feel an effective
nuclear charge of +1, but the Cs valence electron
is a lot farther away from the nucleus. The
electrostatic attraction will be much weaker. So
it’s easier to steal the electron away from Cs.
Source: Conceptual Chemistry by John Suchocki
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
It’s easier to steal an electron from the Li than the
Ne. Li has a smaller effective nuclear charge and
the valence electron is a little farther away from
the nucleus. Li has less “proton pulling power”
than Ne.
Source: Conceptual Chemistry by John Suchocki
Trends in ionization energy
• Ionization energy decreases as you
go down a column – it gets easier &
easier to remove the valence
electron.
• Ionization energy increases as you go
across a row – it gets more difficult to
remove the valence electron.
Periodic properties: Graph shows a repetitive pattern.
Doesn’t have to be a straight line.
Electronegativity
• Relative ability of an atom to attract
electrons in a bond.
• The noble gases tend not to form bonds,
so they don’t have electronegativities.
• Unit = Pauling.
• Fluorine is the most electronegative
element at 4.0.
Formation of a covalent bond
The green atom is
grabbing more than its
fair share of the
electron cloud. It is
more electronegative.
Nonpolar Covalent Bond
Polar Covalant Bond
Trends in electronegativity
• Related to “proton pulling power.”
• Pulling power depends on size of charge
and distance from electrons.
– What’s the trend for effective nuclear charge?
Increases across. Constant down.
– What’s the trend for atomic size?
Decreases across. Increases down.
Trends in electronegativity
• Related to “proton pulling power.”
• Increases as you go across a row.
• Decreases as you go down a column.
• Remember: F is the most electronegative
element!
Reactivity of Metals
• Metals are losers!
• We judge the reactivity of metals by how
easily they give up electrons.
• What property do we look at to assess how
easily metals give up electrons?
Ionization energy: the smaller it is, the easier
the metal loses electrons.
Reactivity of Metals
• The most active metals are Cs and Fr.
They have the smallest ionization
energy.
• For metals, reactivity goes up as
ionization energy decreases.
Trends for Reactivity of Metals
or
Metallic Character
• Increases as you go down.
–Easier to lose electrons!
• Decreases as you go across.
–Harder to lose electrons!
Can you identify the K, Na, and Li in this clip?
Reactivity of Non-metals
• Non-metals are winners!
• We judge the reactivity of non-metals
by how easily they gain electrons.
• What property do we look at to
assess how easily nonmetals gain
electrons?
Electronegativity
Reactivity of Non-metals
• The most active non-metal is fluorine.
• F has the largest electronegativity.
• For non-metals, reactivity increases
as electronegativity increases.
Trend for Reactivity of Non-metals:
Depends on the “proton pulling
power”
• Increases as you go across.
• Decreases as you go down. (Shielded
by more inner-shell electrons.)
Allotrope
• Different forms of an element in the
same phase. Have different
structures and properties.
• O2 and O3 - both gas phase
• Graphite, diamond, buckey balls – all
solid phase carbon.
C60
Graphite and Diamond