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Chapter 10
Periodic Table and Its Trends
1
Groupings of Elements
™Representative elements or main-group elements,
are in the A groups.
™Transition elements are in the B groups.
™Inner transition elements or rare earth elements
are found below the periodic table.
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Cont’d…Groupings of Elements
The inner transition elements are called
lanthanide series and the actinide series.
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Common Names of Groups
Several columns have common, trivial names.
¾Group IA/1 are the alkali metals
¾Group IIA/2 are the alkaline earth metals
¾Group VIIA/17 are the halogens
¾Group VIIIA/18 are the noble gases.
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Cont’d…Common Names of Groups
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Trends in Periodic Table
Periodic table is based on the arrangement of
the elements based on their physical properties.
Trends for atomic radius (size of atom) for
main group elements:
™Atomic radius decreases as you go up a group.
™Atomic radius decreases as you go left to right
across a period.
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Cont’d…Atomic Radius
• Atoms get smaller as you go from bottom to top;
this is because as you go up in a group, there are
fewer energy levels on the atom.
• Atomic radius decreases as you go from left to right;
this is because of the increasing number of protons in
the nucleus as you go from left to right.
• As the number of protons increases, the nucleus pulls
the electrons closer and reduces the size of the atom.
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Metallic Character
The degree of metal character of an element.
Metallic character trends:
decreases from left to right across a period and
decreases from bottom to top in a group.
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Cont’d…Metallic Character
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Physical Properties of Elements
Since elements follow regular patterns in periodic
table, we can predict unknown properties of
elements based on those around it.
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Predicting Chemical Properties
• Group members have similar chemical properties.
• All alkali metals have oxides of the general
formula M2O:
– Li2O, Na2O, K2O, Rb2O, Cs2O, and Fr2O.
Example:
The formula for the chloride of calcium is CaCl2.
What is the formula for the chloride of barium?
– The general formula is MCl2, so the formula
must be BaCl2.
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Blocks of Elements
• Filling of sublevels with electrons:
1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s …
• Periodic table can be broken into blocks of
elements where certain sublevels are being filled:
¾ s block of elements: Groups IA/1 and IIA/2 are
filling s sublevels.
¾ d block of elements Groups IIIB/3 through
IIB/12 are filling d sublevels.
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Blocks and Sublevels
We can predict which sublevel is being filled by a
particular element.
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Noble Gas Core Electron Configurations
• The electron configuration for Na is:
Na: 1s2 2s2 2p6 3s1
• Abbreviate the electron configuration by
indicating the innermost electrons with the symbol
of the preceding noble gas.
• The preceding noble gas with an atomic number
less than sodium is neon, Ne. Rewrite the electron
configuration:
Na: [Ne] 3s1
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Valence Electrons
• Valence electrons: Electrons that have the highest
energy and are furthest away from the nucleus.
These are the electrons (outermost electrons)
which are involved in the chemical reaction.
• The valence electrons are the s and p electrons
beyond the noble gas core.
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Predicting Valence Electrons from
Group Numbers
Based on the American convention, Roman numeral
indicates the number of valence electrons.
– Group IA elements have: 1 valence electron
– Group VA elements have: 5 valence electrons
Based on the IUPAC designations for group numbers,
the last digit indicates the number of valence
electrons.
– Group 14 elements have: 4 valence electrons
– Group 2 elements have: 2 valence electrons
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Electron Dot Formulas
Electron dot formula of an element shows the
symbol of the element surrounded by its valence
electrons.
Use one dot for each valence electron.
Example:
What is the electron dot formula of P?
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Cont’d…Electron Dot Formulas
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Ionization Energy (IE)
IE is the amount of energy required to remove an
electron in the gaseous state.
The closer the electron to the nucleus, the more
energy is required to remove the electron.
General trend in ionization energy:
¾
In a group, ionization energy increases from
bottom to the top.
¾
In a period of elements, ionization energy
increases from left to right.
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Ionic Charge
The charge of an ion is related to the number of
valence electrons on the atom.
• Metals tend to lose electrons and nonmetals tend
to gain electrons.
• Group IA/1 metals lose their one valence electron
to form 1+ ions. Losing valence electron metals
form ions.
Na → Na+ + e-
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Cont’d…Ionic Charge
Group IA/1 metals form 1+ ions,
group IIA/2 metals form 2+ ions,
group IIIA/13 metals form 3+ ions,
and group IVA/14 metals from 4+ ions.
By losing valence electrons, metals achieve a
noble gas configuration.
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Cont’d…Ionic Charge
• Nonmetals can gain electrons to achieve a noble
gas configuration.
Group VA/15 elements form -3 ions,
group VIA/16 elements form -2 ions,
and group VIIA/17 elements form -1 ions.
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Ion Electron Configurations
¾ To write the electron configuration of a positive
ion, remove one electron for each positive charge:
Na → Na+
1s2 2s2 2p6 3s1 → 1s2 2s2 2p6
¾ To write the electron configuration of a negative
ion, add one electron for each negative charge:
O
1s2 2s2 2p4
→
→
O21s2 2s2 2p6
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Review
¾ The elements in the periodic table are arranged by
increasing atomic number and they have
repeating chemical and physical properties.
¾ Atomic radius and metallic character increase
from bottom to top and from left to right across
the periodic table.
¾ The periodic table can be broken down into blocks
where a certain sublevel is being filled.
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Cont’d…Review
¾ Valence electrons are the outermost electrons and
are involved in chemical reactions.
¾ Electron dot formulas indicate the number of
valence electrons.
¾ Ionization energy is the amount of energy that is
required to remove an electron from an atom in
the gaseous state.
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Cont’d…Review
¾ We can predict the charge on the ion of an
element from its position on the periodic table.
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