Chapter 6

Periodic Table
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A chart that organizes all known elements into a grid of horizontal rows, periods, and vertical columns, groups, arranged by increasing atomic number.

Development of Modern Periodic
Table
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Mendeleev, First atomic table, about 63 elements
Organized by atomic mass
Connected atomic mass to properties of elements

Medeleev

Periodic Law
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Henry Moseley, atomic number.
Periodic Law: periodic repetition of chemical and physical properties of the elements.

Modern Periodic Table
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Increasing atomic number
Horizontal rows called periods
Vertical columns called groups or families
Main group, representative, elements
Transition Elements

Modern Periodic Table
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Metals: left side, good conductors, solids usually
Metaloids: Stair step, similar properties of metals and nonmetals
Nonmetals: right side, gases or dull solids, poor conductors

Alkali Metals
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Group 1A – excluding hydrogen
Shiny, malleable, ductile, good conductors
1 valence electron, readily forms +1 cation
Reacts violently with water
Reactivity increases as you go down column.

Alkali Earth Metals
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Group 2A or 2
Ca, Ba, and Sr react with water
2 valence electrons, therefore form
+2 cations.

Halogens
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Highly reactive group
7A or 17
Most are gasses
7 valence electrons, from -1 anion easily

Noble Gasses
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Group 8A or 18
Formally called inert gasses but actually can react, Xe
Full outer energy level

Periodic Trends
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Atomic Radii
Increase down family
Why?
Decreases down period
Why?
Higher effective nuclear charge.

Ionization Energy (IE)
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Energy required to remove an electron from an atom.
How strongly an atom’s nucleus holds onto its valence electron.
↑ IE, less likely to form positive ions
As you move across period IE increases.
Why?
Increased Charge has stronger hold on electrons

Ionization Energy (IE)
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As you move down group the IE decreases.
Why?
Electron shielding, further away

Octet Rule
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States that all atoms tend to gain, lose, or share electrons in order to acquire a full set of eight valence electrons.
Understanding octet rule helps determine ions.
Metals form cations, nonmetals form anions.

Electronegativity
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Relative ability of the atoms to attract electrons in a chemical bond.
Decreases down groups
Increases across period
Francium least electronegative
Fluorine most electronegative