1 GHS Honors Chem Chapter 5 Chemical 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
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
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1
2
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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.