Chemistry Chapter 5

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Chemistry Chapter 5

• The Periodic Law

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Mendeleevs Periodic Table
Dmitri Mendeleev
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Mendeleev organized periodic table

• Vertical columns in atomic mass order
• Made some exceptions to place elements in rows
  with similar properties (Te and I)
• Horizontal rows have similar chemical properties
• Gaps for yet to be discovered elements
• Left questions why didnt some elements fit in
  order of increasing mass? Why did some elements
  exhibit periodic behavior?

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Moseley

• Discovered that periodic table was in atomic
  number order, not atomic mass order
• Explained the Te-I anomaly

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Periodic Law

• Physical and chemical properties of the elements
  are periodic functions of their atomic numbers

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Modern Periodic Table

• Discovery of noble gases yields new family (Group
  18 aka inert gases)
• Lanthanides (58 - 71)
• Actinides (90 103)

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Periods and Blocks of the Periodic Table

• Periods horizontal rows
• Groups/Families vertical columns these
  elements share similar chemical properties (they
  have the same number of valence electrons)
• Blocks periodic table can be broken into blocks
  corresponding to s, p, d, f sublevels

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Orbital filling table
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Blocks and Groups s block

• Group1 The alkali metals
• One s electron in outer shell
• Soft, silvery metals of low density and low
  melting points
• Highly reactive, never found pure in nature

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Blocks and Groups s block

• Group 2 Alkaline Earth Metals
• 2 s electrons in outer shell
• Denser, harder, stronger, less reactive than
  Group 1
• Too reactive to be found pure in nature

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Periodic Table with Group Names
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The Properties of a Group the Alkali Metals

• Easily lose valence electron
• (Reducing agents)
• React violently with water
• React with halogens to form salts

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Blocks and Groups d block

• Groups 3 -12
• Metals with typical metallic properties
• Referred to as transition metals
• Group number sum of outermost s and d electrons

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Properties of Metals

• Metals are good conductors of heat and
  electricity
• Metals are malleable
• Metals are ductile
• Metals have high tensile strength
• Metals have luster

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Examples of Metals
Potassium, K reacts with water and must be stored
in kerosene
Copper, Cu, is a relatively soft metal, and a
very good electrical conductor.
Zinc, Zn, is more stable than potassium
Mercury, Hg, is the only metal that exists as a
liquid at room temperature
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Blocks and Groups p block

• Groups 13-18
• Properties vary greatly metals, metalloids, and
  nonmetals
• Group 17 halogens are most reactive of non
  metals
• Group 18 noble gases are NOT reactive

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Properties of Nonmetals
Carbon, the graphite in pencil lead is a great
example of a nonmetallic element.

• Nonmetals are poor conductors of heat and
• electricity
• Nonmetals tend to be brittle
• Many nonmetals are gases at room temperature

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Examples of Nonmetals
Microspheres of phosphorus, P, a reactive
nonmetal
Sulfur, S, was once known as brimstone
Graphite is not the only pure form of carbon, C.
Diamond is also carbon the color comes from
impurities caught within the crystal structure
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Properties of Metalloids
Metalloids straddle the border between metals and
nonmetals on the periodic table.

• They have properties of both metals and
  nonmetals.
• Metalloids are more brittle than metals, less
  brittle than most nonmetallic solids
• Metalloids are semiconductors of electricity
• Some metalloids possess metallic luster

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Silicon, Si A Metalloid

• Silicon has metallic luster
• Silicon is brittle like a nonmetal
• Silicon is a semiconductor of electricity

Other metalloids include

• Boron, B
• Germanium, Ge
• Arsenic, As
• Antimony, Sb
• Tellurium, Te

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Blocks and Groups f block

• Lanthanides shiny metals similar to group 2
• Actindes all are radioactive plutonium
  lawrencium are man-made

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Determination of Atomic Radius
Half of the distance between nucli in covalently
bonded diatomic molecule
"covalent atomic radii"
Periodic Trends in Atomic Radius

• Radius decreases across a period

Increased effective nuclear charge due to
decreased shielding

• Radius increases down a group

Addition of principal quantum levels
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Table of Atomic Radii
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Ionization Energy - the energy required to
remove an electron from an atom

• Increases for successive electrons taken from
• the same atom

• Tends to increase across a period

Electrons in the same quantum level do not
shield as effectively as electrons in inner
levels
    Irregularities at half filled and filled
sublevels due to extra repulsion of
electrons paired in orbitals, making them
easier to remove

• Tends to decrease down a group

Outer electrons are farther from the nucleus
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Ionization of Magnesium
Mg 738 kJ ? Mg e-
Mg 1451 kJ ? Mg2 e-
Mg2 7733 kJ ? Mg3 e-
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Table of 1st Ionization Energies
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Another Way to Look at Ionization Energy
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Ionic Radii
Cations

• Positively charged ions

• Smaller than the corresponding
• atom

Anions

• Negatively charged ions

• Larger than the corresponding
• atom

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Table of Ion Sizes
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Electronegativity
A measure of the ability of an atom in a
chemical compound to attract electrons

• Electronegativities tend to increase across
• a period
• more nuclear charge, more power to
  attract electrons

• Electronegativities tend to decrease down a
  group or remain the same
• additional energy levels result in less
  attraction to the nucleus

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Periodic Table of Electronegativities