Monday
October 15, 2012
(Chemical Periodicity;
WS – Periodic
Properties)
Bell Ringer
Monday, 10-15-12
Henry Moseley studied xray spectra of several
elements in a row of the Periodic Table. He
found that each element had one more proton
than the element immediately to its left.
Which statement BEST describes Moseley's
contribution to the modern Periodic Table?
A. recognizing that elements in the periodic
table have similar properties
B. arranging elements in the periodic table
based on their properties
C. predicting the properties of missing
elements in the periodic table
D. providing a basis for ordering elements in the
Periodic Table
Bell Ringer
Monday, 10-15-12
Which of the following describes
The number of valence
the properties of noble gases?
electrons in Group 2
A. They have high boiling points
elements is __________ .
B. They are highly reactive .
A0
C.
B1
They are generally unreactive.
C2
D They are solid at
D3
room temperature.
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Assignment
Currently Open
Summative
or
Formative?
Date Issued
Date Due
QUIZ 6
S3
10/5
10/5
10/19
QUIZ 7
S4
10/12 10/12
10/26
WS – The
Periodic Law
F1
10/12
10/17
Date Into
GradeSpeed
Final Day
10/19
Question
What is meant by the term “periodicity?”
In general terms, periodicity is defined as the quality of recurring
at regular intervals .
Chemistry defines periodicity as similarities in chemical properties
recurring at regular intervals .
This leads to the Periodic Law, which states that the physical and
chemical properties of the elements are periodic functions of their
atomic numbers.
Five Properties of Elements that
Display Periodicity
Atomic Radius
Ionization Energy
Electron Affinity
Ionic Radius
Electronegativity
Atomic Radius
Atomic radius may be defined as one-half the
distance between the nuclei of identical atoms
that are bonded together.
A picometer
(pm) is a
metric unit of
length equal
to one
trillionth of a
meter.
1x10-12
meter
On your
metric
staircase, this
would be 9
steps below
milli-
Atomic Radius
Atomic radii decrease from left to right across a
period because of the increasing positive charge
of the nuclei (more and more p+) pulling the ecloser and closer.
Generally
speaking, the
smaller
size of the
atoms get
smaller as you
move from left
to right across
a period.
Atomic Radius
Atomic radii increase from top to bottom down
a group because of e- occupying sublevels in
successively higher main energy levels.
Generally
speaking, the
size of the
atoms get
larger as you
move from top
to bottom
down a group.
larger
Even thought the lines in each period are not
identical, they show a similarity that creates a
pattern. This is NOT randomness!
Ionization Energy
Ionization energy may be defined as
the energy required to remove one
electron from a neutral atom of an
element.
This property determines the extent to which an
atom is capable of losing electrons in order to
begin the chemical bonding process.
Ionization Energy
In general, ionization energies of the main-group
elements increase across each period. This increase is
caused by increasing nuclear charge. A higher charge
more strongly attracts electrons in the same energy
level.
Generally
speaking, the
increases
energy required
for an atom to
lose electrons
increases as you
move from left to
right across a
period.
Ionization Energy
Among the main-group elements, ionization energies
generally decrease down the groups. Electrons
removed from atoms of each succeeding element in a
group are in higher energy levels, farther from the
nucleus.
Generally
speaking, the
energy required
to lose electrons
get less as you
move down a
group.
Therefore, they
are removed
more easily.
decrease
Electron Affinity
.
Electron affinity is defined as the energy
change that occurs when an electron is
acquired by a neutral atom.
Most atoms release energy when they acquire an
electron - the quantity of energy released is represented
by a negative number.
Some atoms must be “forced” to gain an electron by the
addition of energy - the quantity of energy absorbed is
represented by a positive number.
Electron Affinity
In general, as electrons add to the same p sublevel of
atoms with increasing nuclear charge, electron
affinities become more negative across each period
within the p block, although there are exceptions.
For example, adding
an electron to a
nitrogen atom gives
a half-filled p
sublevel. This
occurs much more
easily than forcing
an electron to pair
with another
electron in an orbital
of the already halffilled p sublevel of a
oxygen atom.
negativity increases
Electron Affinity
As a general rule, electrons add with greater difficulty down a
group. This pattern is a result of two competing factors.
The first is a slight increase in effective nuclear charge down
a group, which increases electron affinities. The second is
an increase in atomic radius down a group, which decreases
electron affinities.
In general,
the size effect
predominates.
decrease
Ions
• Ions are created when neutral atoms lose or
gain electrons, and the number of protons no
longer matches the number of electrons.
• The atom is no longer electrically neutral and
has an overall + or – charge.
• If an atoms loses one or more electrons, it now
has more protons than electrons and takes on a
positive charge.
• If an atoms gains one or more electrons, it now
has more electrons than protons and takes on a
negative charge.
Ions
• Positive and negative ions have specific
names.
– A positive ion is known as a cation.
– A cation is formed by the loss of one or more
electrons always leads to a decrease in atomic
radius because the removal of the highestenergy-level electrons results in a smaller
electron cloud.
– Also, the remaining electrons are drawn
closer to the nucleus by its unbalanced
positive charge.
Ions
• Positive and negative ions have specific
names.
– A negative ion is known as an anion.
– The formation of an anion by the addition of one or
more electrons always leads to an increase in atomic
radius.
– This is because the total positive charge of the nucleus
remains unchanged when an electron is added to an
atom or an ion.
– So the electrons are not drawn to the nucleus as
strongly as they were before the addition of the extra
electron.
– The electron cloud also spreads out because of greater
repulsion between the increased number of electrons.
Ions
Within each period, the metals at the left
tend to form cations and the non-metals at
the upper right tend to form anions.
Lose electrons to form
positive cations
Gain electrons
to form
negative
anions
Ionic Radius
Cationic radii decrease across a period because the electron cloud
shrinks due to the increasing nuclear charge acting on electrons in
the same main energy level. Starting with Group 15, in which atoms
assume stable noble-gas configurations by gaining three electrons,
anions are more common than cations.
Anionic radii
decrease across
each period for the
elements in
Groups 15–18. The
reasons for this
trend are the same
as the reasons that
cationic radii
decrease from left
to right across a
period.
decrease
Ionic Radius
As they are in atoms, the outer electrons in both cations
and anions are in higher energy levels as one reads down a
group. Therefore, just as there is a gradual increase of
atomic radii down a group, there is also a gradual
increase of ionic radii.
increase
Electronegativity
The outer-most, highest energy
level electrons in an atom’s
electron cloud are called its
“valence” electrons.
Valence electrons are the ones that
participate in chemical bonding –
the force that hold elements
together to form compounds.
When two atoms are bonded
together, one of the atoms may
“tug” harder at the participating
valence electrons harder than the
other atom does.
Electronegativity is a measure of
the ability of an atom in a
chemical compound to attract
electrons.
Electronegativity
Electronegativity values tend to
increase across each period,
although there are exceptions.
increase
Electronegativity
Electronegativity values tend to
either decrease down a group or
remain about the same.
Decrease/remain
same
Electronegativity
The alkali and alkaline-earth metals are the
least electronegative elements.
In compounds, their atoms have a low
attraction for electrons.
least electronegative
Electronegativity
Nitrogen, oxygen, and the halogens are the
most electronegative elements.
Their atoms attract electrons strongly in
compounds.
most electronegative
Electronegativity
The Noble gases are unusual in that some of them do not
form compounds and therefore cannot be assigned
electronegativity values.
But when a Noble
gas does form a
compound, its
electronegativity
is rather high,
similar to the
values for the
halogens.
Electronegativity
The combination of the period and group
trends in electronegativity results in the
highest values belonging to the elements in the
upper right of the periodic table.
The lowest values belong to the elements in the
lower left of the table.
highest
lowest
Electronegativity
The alkali metals cesium and francium have the
lowest electronegativity values at 0.7.
The halogen fluorine has the highest
electronegativy value at 4.0.
highest
lowest
Worksheet
Periodic Properties