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Periodicity

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Classification of the Elements u OBJECTIVES: Explain why you can infer the properties of an element based on those of other elements in the periodic table.

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Classification of the Elements u OBJECTIVES: Use electron configurations to classify elements as noble gases, main group elements, transition metals, or inner transition metals.

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Periodic Table Revisited u Russian scientist Dmitri Mendeleev taught chemistry in terms of properties. u Mid 1800’s - molar masses of elements were known. u Wrote down the elements in order of increasing mass. u Found a pattern of repeating properties.

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Mendeleev’s Table u Grouped elements in columns by similar properties in order of increasing atomic mass. u Found some inconsistencies - felt that the properties were more important than the mass, so switched order. u Also found some gaps. u Must be undiscovered elements. u Predicted their properties before they were found.

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The modern table u Elements are still grouped by properties. u Similar properties are in the same column. u Order is by increasing atomic number. u Added a column of elements Mendeleev didn’t know about. u The noble gases weren’t found because they didn’t react with anything.

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u Horizontal rows are called periods u There are 7 periods

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Vertical columns called groups Elements are placed in columns by similar properties Also called families

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1A 2A3A4A5A6A 7A 8A 0 u The elements in the A groups are called the representative elements outer s or p filling

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The group B are called the transition elements u These are called the inner transition elements, and they belong here

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u Group 1A are the alkali metals u Group 2A are the alkaline earth metals

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u Group 7A is called the Halogens u Group 8A are the noble gases

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Why? u The part of the atom another atom sees is the electron cloud. u More importantly the outside orbitals. u The orbitals fill up in a regular pattern. u The outside orbital electron configuration repeats. u The properties of atoms repeat.

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1s11s1 1s 2 2s 1 1s 2 2s 2 2p 6 3s 1 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 1 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 6 6s 1 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 6 6 s 2 4f 14 5d 10 6p 6 7s 1 H 1 Li 3 Na 11 K 19 Rb 37 Cs 55 Fr 87

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He 2 Ne 10 Ar 18 Kr 36 Xe 54 Rn 86 1s21s2 1s 2 2s 2 2p 6 1s 2 2s 2 2p 6 3s 2 3p 6 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 6 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 6 6s 2 4f 14 5d 10 6p 6

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u Alkali metals all end in s 1 u Alkaline earth metals all end in s 2 u really should include He, but it fits better later. u He has the properties of the noble gases. s2s2 s1s1 S- block

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Transition Metals -d block d1d1 d2d2 d3d3 s1d5s1d5 d5d5 d6d6 d7d7 d8d8 s 1 d 10 d 10

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The P-block p1p1 p2p2 p3p3 p4p4 p5p5 p6p6

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F - block u inner transition elements

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u Each row (or period) is the energy level for s and p orbitals

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u d orbitals fill up after previous energy level, so first d is 3d even though it’s in row d

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u f orbitals start filling at 4f f 5f

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Writing electron configurations the easy way

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Electron Configurations repeat u The shape of the periodic table is a representation of this repetition. u When we get to the end of the column the outermost energy level is full. u This is the basis for our shorthand.

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The Shorthand u Write symbol of the noble gas before the element, in [ ]. u Then, the rest of the electrons. u Aluminum’s full configuration: 1s 2 2s 2 2p 6 3s 2 3p 1 u previous noble gas Ne is: 1s 2 2s 2 2p 6 u so, Al is: [Ne] 3s 2 3p 1

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More examples u Ge = 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 2 Thus, Ge = [Ar] 4s 2 3d 10 4p 2 u Hf = 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 6 6s 2 4f 14 5d 2 Thus, Hf = [Xe]6s 2 4f 14 5d 2

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The Shorthand Again Sn- 50 electrons The noble gas before it is Kr [ Kr ] Takes care of 36 Next 5s 2 5s 2 Then 4d 10 4d 10 Finally 5p 2 5p 2

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