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GHS Honors Chem
Chapter 5Chemical Periodicity
GHS Honors Chem
Classification of the Elements
OBJECTIVES:� Explain why you can infer the
properties of an element based on those of other elements in the periodic table.
� Use electron configurations to classify elements as noble gases, representative elements, transition metals, or inner transition metals.
GHS Honors Chem
Periodic Table Revisited� Russian scientist Dmitri Mendeleev
taught chemistry in terms of properties.
� Mid 1800’s - molar masses of elements were known.
� Wrote down the elements in order of increasing mass.
� Found a pattern of repeating properties.
GHS Honors Chem
Mendeleev’s Table� Grouped elements in columns by similar
properties in order of increasing atomic mass.
� Found some inconsistencies - felt that the properties were more important than the mass, so switched order.
� Also found some gaps.� Must be undiscovered elements.� Predicted their properties before they
were found.
GHS Honors Chem
Mendeleev's Periodic Table(1871)
GHS Honors Chem
The Modern Periodic Table� Elements are still grouped by properties.� Similar properties are in the same
column.� In 1913, Moseley changed the order to
increasing atomic number.� This added a column of elements
Mendeleev didn’t know about.� The noble gases weren’t found because
they didn’t react with anything.
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GHS Honors Chem
� Horizontal rows are called Periods� There are 7 periods
76
1
2
34
5
GHS Honors Chem
Vertical columns called groupsElements are placed in columns by similar propertiesAlso called families
GHS Honors Chem
1A
2A 3A 4A 5A 6A 7A
8A0
The elements in the A groups are called the REPRESENTATIVEelementsouter s or p filling
GHS Honors Chem
The group B are called the transition elements
These are called the inner transition elements, and they belong here
GHS Honors Chem
� Group 1A are the alkali metals� Group 2A are the alkaline earth metals
GHS Honors Chem
� Group 7A is called the Halogens� Group 8A are the Noble Gases
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GHS Honors Chem
Why is the Periodic Table arranged in Groups and Periods?
� The part of the atom another atom sees is the electron cloud.
� More importantly the outside orbitals. � The orbitals fill up in a regular pattern.� The outside orbital electron
configuration, or VALENCE electron configuration, repeats.
� The properties of atoms repeat.
GHS Honors Chem
1s1
1s22s1
1s22s22p63s1
1s22s22p63s23p64s1
1s22s22p63s23p64s23d104p65s1
1s22s22p63s23p64s23d104p65s24d10 5p66s1
1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p67s1
H1
Li3
Na11
K19
Rb37
Cs55
Fr87
Group 1A Alkali metals• 1 Valence Electron
• s1 configuration• Become +1 ions to
obtain the OCTET ofelectrons
GHS Honors Chem
4Be: 1s22s2
12Mg: 1s22s22p63s2
20Ca: 1s22s22p63s23p64s2
38Sr: 1s22s22p63s23p64s23d104p65s2
56Ba: 1s22s22p63s23p64s23d104p65s24d10
5p66s2
88Ra: 1s22s22p63s23p64s23d104p65s24d105p6
6s24f145d106p67s2
Group 2A Alkaline Earth Metals• 2 Valence Electrons
• s2 configuration• Become +2 ions to
obtain OCTET ofelectrons
GHS Honors Chem
1s22s22p5 9F
1s22s22p63s23p517Cl
1s22s22p63s23p64s23d104p5 35Br
1s22s22p63s23p64s23d104p65s24d105p5 53I
1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p5 85At
Group 7A Halogens• 7 Valence Electrons• s2p5 configuration• Become -1 ions to achieve
their octet of electrons
GHS Honors Chem
He2
Ne10
Ar18
Kr36
Xe54
Rn86
1s2
1s22s22p6
1s22s22p63s23p6
1s22s22p63s23p64s23d104p6
1s22s22p63s23p64s23d104p65s24d105p6
1s22s22p63s23p64s23d104p65s24d10
5p66s24f145d106p6
Group 8A Noble Gases• 8 Valence Electrons• s2p6 configuration• Not reactive, have their
octet of electrons
GHS Honors Chem
Can we determine an element simply from the Valence Electron
Configuration?
Let’s try it …
1. 3s2
2. 5s25p4
3. 4s23d6
MgTeFe
4
GHS Honors Chem
Lewis Dot Structures� Lewis Dot structures are helpful in
visualizing bonding between atoms.� Dots correspond to the number of
valence electrons. These are the electrons that are involved in interactions between atoms.
� Dots are placed around the element’s symbol, 1 at a time, until pairing is necessary.
GHS Honors Chem
Lewis Dot StructuresK CaInCPSF
What about ions?02-
Br-
The number of unpaired dots corresponds to the number of bonds
that the atom can form in a compound.
GHS Honors Chem
Lewis Dot Structures