Transcript Periodic Trends

Periodic Trends
Section 6.3
The 4 Trends
 Because of the periodic law, properties
of elements change in predictable ways.
This section looks at the following
trends:
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Atomic Radius
Ionic Radius
Ionization Energy
Electronegativity
Atomic Radius
 Because there is not a clearly defined
edge on an atom, the atomic radius is
defined as half the distance between two
adjacent nuclei in a crystal of the
element
 Electrostatic attraction is the
attraction of an electron for a proton. The
more protons and electrons that are
present in an atom the stronger the
electrostatic attraction
 Atoms get smaller to the right because
there are more electrons in the same
energy level and a greater electrostatic
attraction
 Atoms get larger moving down because of
more energy levels and therefore being
farther from the nucleus. Also, the
shielding effect causes electrons to repel
each other, making them bigger.
Trends in Atomic Radius
Ionic Radius
 Ions are formed when atoms gain or lose
electrons and become charged particles
 Octet Rule – all atoms will gain or lose
electrons in order to acquire a full set of
eight (two) valence electrons
Determining Oxidation
Numbers
 When atoms lose electrons and become
positively charged:
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They become smaller because of the loss
of an energy level (valence electron)
They also become smaller because of less
electrostatic repulsion between the
electrons causing a greater pull of the
remaining electrons to the nucleus
Determining Oxidation
Numbers
 When atoms gain electrons, they
become negatively charged:
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They always get bigger because the
electrons push each other apart
(electrostatic repulsion). The increased
distance between the outer electrons
results in a larger radius.
Periodic Trends in Ionic
Radius
 Trends within periods – Generally the left
side of the periodic table forms smaller,
positive ions. Around family 5A or 6A,
the right side of the periodic table forms
larger, negative ions
 Trends within groups – the outer
electrons are in higher energy levels as
you go down a family causing them to
increase in size
Periodic Trends of Ionic
Radius
Ionization Energy
 Energy required to remove an electron
from a gaseous atom
Periodic Trends in Ionization
 The larger an atom is, the easier it is to
lose an electron because the distance
between the nucleus and the electron is
greater
Electronegativity
 The relative ability of an atom to attract
electrons in a chemical bond
 The smaller the atom, the stronger the
electronegativity because the protons
are closer to the valence electrons.
Electronegativity
 The larger the atom is, the lower the
electronegativity because the valence
electrons are further from the protons in
the nucleus
 Electronegativity is measured in
“Paulings” on a scale of 1  4
Periodic Trend of
Electronegativities