Welcome to the Periodic Kingdom

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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 regionsyet it accounts for
everything material in our actual world1 1
Davis, R.E. et al, Modern Chemistry TE, Holt,
Rinehart and Wiston company, NYC 2002, p.135.
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Periodicityby Marta de Ortiz de Zevallos

• 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.

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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.

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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)

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How is the modern periodic table different from
Mendeleevs periodic table?
The modern periodic table is similar to
Mendeleevs 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.
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PERIODIC LAW The properties of the elements
repeat periodically when they are arranged in
increasing order by their atomic numbers.
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The Periodic Table

• Metals are at the left (red)
• Non-metals at the right, except for H (blue)
• Metalloids are between metals and non-metals and
  they have properties of both.

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More about the PT
It is divided into horizontal rows called periods
and vertical columns called groups.

• Groups are also called families
• Why?
• Because the elements in a group share properties
  like the members of a family.

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What is the charge?
1
2
3
4-
3-
2-
1-
?
?
?
?
The non metals in

• Group 17 (halogens) 1-

• Group 1 (alkali metals) 1

Group 16 2-
Group 2 (alkaline earth metals) 2
Group 15 3-
Group 13 (boron group) 3
Group 14 4-
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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 charge

Why?

• Because they all tend to become isoelec-tronic
  with the noble gases to complete their outermost
  s and p orbitals.

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Remember that the noble gases are the happy
family!
They have their outer level complete. They dont
want more electrons and they dont need to
give away electrons.
all the elements want to be like the noble
gases so they tend to become isoelectronic with
them
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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

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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/
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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.
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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 e-
• The 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/
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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.

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First Ionization Energy vs atomic number
1st IE
http//wulff.mit.edu/pt/pert9.html
Atomic Number
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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

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• 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 lt 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- gt F

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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

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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- gt F- gt Na gt Mg2

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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 its 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.

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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/
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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)