Transcript “Welcome to the Periodic Kingdom…

“Welcome to the Periodic
Kingdom…
…This is a land of the imagination, but it is
closer to reality than it appears to be.
This is the Kingdom of chemical elements,
the substances from which everything
tangible is made.
It is not an extensive country, for it consists
of only a hundred or so regions…yet it
accounts for everything material in our actual
world”1
1 Davis,
R.E. et al, Modern Chemistry TE, Holt, Rinehart and Wiston
company, NYC 2002, p.135.
Periodicity
by Marta de Ortiz de Zevallos
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To understand how
the periodic table
was created
and how it can be
used
allows you to
predict
“the properties of
elements even if
you never saw
them”.
Before the development of the modern
atomic theory, many elements were
discovered. To be able to understand and
predict their properties it was necessary
to organize them.
In 1869, Dimitri Mendeleev published
his periodic table.
In his table the elements were
arranged in order of increasing
atomic mass.
The properties of the elements
arranged in this way repeated
periodically in vertical columns.
Mendeleev published another version of the periodic
table in 1872 in which he left blank spaces for
elements that were not known yet. He predicted their
existence and the properties they should have.
These elements were
later discovered and the
properties he predicted
were very accurate for
the time.
His work “can be
thought of as similar to
putting together a large
puzzle.” (Heath
Chemistry)
How is the modern periodic table different
from Mendeleev’s periodic table?
The modern periodic table is similar to
Mendeleev’s periodic table, but with a
difference proposed by Henry Moseley to
solve some discrepancies between some
elements (Ar and K , I and Te). If they are
put in order of increasing atomic mass
their properties do not match with those of
the elements in the same column.
In the modern periodic table the
elements are in order of increasing
atomic number instead of mass.
PERIODIC LAW: “ The properties of the
elements repeat periodically when they
are arranged in increasing order by their
atomic numbers.
The Periodic Table
http://antoine.fsu.umd.edu/chem/senese/101/matter/slides/sld013.htm
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Metals are at the left (red)
Non-metals at the right, except for H (blue)
Metalloids are between metals and nonmetals and they have properties of both.
More about the PT…
It is divided into
horizontal rows called
periods and vertical
columns called groups.
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Groups are also called
families
Why?
Because the elements in a
group share properties
like the members of a
family.
1+ 2+
What is the charge?
3+ 4- 3- 2- 1-
?
http://antoine.fsu.umd.edu/chem/senese/101/matter/slides/sld013.htm
The non metals in:
Group 17 (halogens): 1Group 1 (alkali metals): 1+
Group 16: 2Group 2 (alkaline earth metals) : 2+
Group 15: 3Group 13 (boron group): 3+
Group 14: 4-
Now that you have learned the electron
configuration of elements, what relationship do
you see between the configuration, the position in
the table and the charge the elements can get ?
The elements in the same group
have the same outer configuration.
 They tend to
acquire the same
Why?
charge
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Because they all tend to become isoelectronic with the noble gases to complete
their outermost s and p orbitals.
Remember that
the noble gases
are the happy
family!
They have their outer level
complete. They don’t “want”
more electrons and they don’t
“need” to give away electrons.
… all the elements “want” to be like the noble
gases so they tend to become isoelectronic with
them
How do properties vary in the PT?
•Metallic properties:
•1) Increase from top to bottom and
from right to left.
Most active metals: Cs & Fr
•So the activity of the alkali metals
increases from top to bottom.
However the activity of the
halogens (non metals of group 17)
increases from bottom to top.
•The most active non metal is F
More physical properties
Atomic radius (it gives a measure of the size of
the atom)
The atomic radii decrease from left to right
and from bottom to top in the PT.
http://ull.chemistry.uakron.edu/genobc/Chapter_03/
More physical properties
The atomic radii decrease from left to right in the PT.
Why?
Because, as we move from left to right through a
period of the PT, the nuclear charge increases
attracting more the electrons that are added to the
same energy level.
The atomic radii increase from top to bottom. Why?
Because as we move down a group the electrons are
added to higher energy levels (electrons have the same
outermost but with higher principal quantum number),
so they are less attracted by the nucleus. Besides that,
as there are more inner electrons, there is more
shielding effect, wich also reduces the attraction of the
outer electrons by the nucleus.
More physical properties
First Ionization Energy
Is the energy necessary to remove an electron
from a neutral gaseous atom.
Can be represented by the equation:
X(g)+ IE  X+ + eThe smaller the IE, the greater the tendency of
the element to form a positive ion.
In the PT, especially for
the representative
elements, the IE increases
from bottom to top and
from left to right.
http://ull.chemistry.uakron.edu/genobc/Chapter_03/
In the PT…
In general, the IE increases from left to
right in the PT.
However some exceptions are observed in each
period.
For example in period 2, when going from Be to B
and from N to O, the IE decreases.
In the case of Be to B the decrease is due to the
filled 2s orbital which provides, in the case of B,
some shielding to the electron in p.
In the case of N to O the decrease is due to the
extra repulsion in the doubly occupied p orbital.
First Ionization Energy vs atomic number
1st IE
http://wulff.mit.edu/pt/pert9.html
Atomic Number
More physical properties
Ionic Size
There are various factors that affect the size of
an ion:
.The nuclear charge
.The repulsion of electrons
.The level of energy of the outer electrons
Comparing the ion with the parent atom:
• Positive ions are smaller than the neutral atom
• Because they have the same nuclear charge
attracting less electrons, therefore the attraction
is stronger.
• For example K+ < K
• Negative ions are larger than the neutral atom
• Because they have the same nuclear charge
attracting more electrons, therefore the
attraction is weaker.
• For example F- > F
In the PT…
In a group, the ionic size increases from top
to bottom
The reason is the same as for the atomic
radius.
e- added to higher energy levels and more
shielding effect.
In a period, it depends of the type of ions
But negative ions decrease from left to right
and positive ions also decrease from left to
right.
e- are added to the same level and Z increases
In the PT…
The size of isoelectronic ions (ions
with the same number of electrons)
decreases as the nuclear charge (Z)
increases, because there are more
protons to attract the same amount of
electrons distributed in the same levels
and with the same shielding effect.
Example: O2- > F- > Na+ > Mg2+
More physical properties
Electron Affinity
Is the energy change associated with the addition of an
electron to a gaseous atom.
X(g)+ + e- X- (g)
. It can be energy released or absorbed. When it is
negative it’s energy released. The greater the tendency
of the element to form negative ions the more negative
the electron affinity.
. Electron affinities usually become more negative
from left to right in a period of the PT.
. In going down a group the electron affinities become
more positive because the electrons added are farther
from the nucleus.The change is small though and there
are several exceptions.
Electronegativity…
Electronegativity is the ability of an atom in a
molecule to attract shared electrons to itself.
. The electronegativity increases from bottom to
top and from left to right.
. Fluorine is the most electronegative element.
. Cesium and Francium are the least
electronegative elements.
http://ull.chemistry.uakron.edu/genobc/Chapter_03/
Other properties like melting and boiling points and
densities, depend on the attraction between particles.
However we can observe some patterns in the
melting points when moving through a period of
the PT.
• The melting point increases until group 14 which
includes solids such as C and Si which form giant
molecules with covalent bonds between the atoms.
Then the melting points decrease drastically as we
get to groups 15, 16, 17 and especially the noble
gases in group 18. (We will talk more about this
when we study interparticle forces)