Transcript periodic law

INTRODUCTORY CHEMISTRY
Concepts & Connections
Fifth Edition by Charles H. Corwin
Chapter
10b
Periodic
Trends
Christopher G. Hamaker, Illinois State University, Normal IL
© 2008, Prentice Hall
10.11 The Periodic Law
• The periodic law states that the properties of elements
recur in a repeating pattern when arranged according to
increasing atomic number.
• The arrangement of the periodic table means that the
physical properties of the elements follow a regular
pattern.
Chapter 6
2
Periodic Trends
• Not all properties can be predicted by their
position on the periodic table…we can predict
Atomic Size
Ion Size
Ionization Energy
Electronegativity
Chapter 6
3
“Shielding”
Shielding is an effect felt by valence (outer)
electrons.
Layers of core (inner) electrons “shield” or protect
the outer electrons from the nucleus- so they feel less
of an attraction to the nucleus.
Electrons in the same valence shell do not shield one
another
Chapter 6
4
Atomic Radius
• This figure shows the atomic radii of the main
group elements.
• The general
trend in
atomic radius
applies to the
main group
elements, not
the transition
elements.
Chapter 6
5
Atomic Radius
We can look at the size of atoms, or their atomic
radius.
There are two trends for atomic radii:
Atomic radius increases as you go down a group.
Atomic radius decreases as you go left to right
across a period.
Chapter 6
6
Atomic Radius– the “Why”
• Atoms get larger as you go down a column because 3
things occur:
– there are more energy levels between outer e- and nucleus
– distance from the nucleus increases
– increased amount of shielding
• Atomic radius decreases as you travel left to right across
the periodic table because of the increased nuclear effect.
(the number of protons in the nucleus increases with no
additional shielding) As the number of protons increases,
the nucleus pulls the electrons closer and reduces the size
of the atom.
Chapter 6
7
Ionization Energy
• The ionization energy of an atom is the amount of
energy required to remove an electron in the
gaseous state.
• In general, the ionization energy decreases as you
go from the top to the bottom in a group.
• In general, the ionization energy increases as you
go from left to right across a period of elements.
• The closer the electron to the nucleus, the more
energy is required to remove the electron.
Chapter 6
8
Ionization Energy Trend
• Figure
shows the
trend for
the first
ionization
energy of
the
elements.
Chapter 6
9
Sizes of Ions
• Cations (metal ions)
are smaller than
their parent atoms:
– The outermost
electron is removed
and repulsions
between electrons
are reduced.
Chapter 6
10
Sizes of Ions
• Anions (nonmetal
ions) are larger than
their parent atoms”
– Electrons are added
and repulsions
between electrons
are increased.
Chapter 6
11
Sizes of Ions
• Ions increase in size as
you go down a
column:
– This increase in size is
due to the increasing
energy levels
Chapter 6
12
Sizes of Ions
• Ionic size decreases across a period due to an
increasing nuclear effect.
Chapter 6
13
Electronegativity
• Each element has an innate ability to attract
valence electrons.
• Electronegativity is the ability of an atom to
attract electrons in a chemical bond.
• Linus Pauling devised a method for measuring the
electronegativity of each of the elements.
• Fluorine is the most electronegative element.
Chapter 6
14
Electronegativity
• Electronegativity increases as you go left to right
across a period.
• Electronegativity increases as you
go from bottom to top
in a family.
Chapter
Chapter12
6
15
Electronegativity Differences
• The electronegativity of H is 2.1; Cl is 3.0.
• Since there is a difference in electronegativity
between the two elements (3.0 – 2.1 = 0.9), the
bond in H–Cl is polar.
• Since Cl is more electronegative, the bonding
electrons are attracted toward the Cl atom and
away from the H atom. This will give the Cl atom
a slightly negative charge and the H atom a
slightly positive charge.
Chapter 6
16