The Periodic Table
Jan 18, 2016
The Periodic Table
Valence Electrons
• Electrons farthest away from the nucleus are most loosely held.
• Ranges from 1 to 8 valence electrons
• Many properties of the atom, and therefore of an element, are determined by the number of valence electrons.
http://www.tutorvista.com/content/science/science-i/structure-atom/valence-shell-electron.php
Pre-Periodic Table Chemistry …
…was a mess!!!
No organization of elements.
Imagine going to a grocery store with no organization!!
Difficult to find information.
Chemistry didn’t make sense.
Dmitri Mendeleev: Created The Periodic Table
HOW HIS WORKED… Elements arranged in
rows (periods) by increasing atomic mass.
Elements arranged in columns (families) by the way they reacted.
SOME PROBLEMS… Left blank spaces for
what he said were undiscovered elements. (Turned out he was right!)
Pattern of increasing atomic mass was broken to keep similar reacting elements together.
http://upload.wikimedia.org/wikipedia/commons/b/b3/Medeleeff_by_repin.jpg
The Current Periodic Table
In 1913, Henry G.J. Moseley, an English scientist, arranged the elements based on increasing atomic number.
http://www.chemistryexplained.com/Ma-Na/Moseley-Henry.html
Groups
Vertical columns are called groups or families Groups are numbered 1 to 18.
Groups…Here’s Where the Periodic Table Gets Useful!!
Elements in the same group have similar chemical and physical properties!!
Example: Elements in Group 1 are highly reactive and can be explosive in water.
www.pearsonsuccessnet.com
They have the same number of valence electrons.
http://www.tutorvista.com/content/science/science-i/structure-atom/valence-shell-electron.php
Why?
Periods
• Horizontal rows numbered 1 to 7.
• Elements in the same period have the same number of electron rings or energy levels.
Metals:Metals:
•Left/Middle of Periodic Table•Give up valence electron in a reaction• Shiny, metallic• Conduct heat and electricity• Malleable and ductile (reshape)
Copper
Nickel
Aluminum
Gold
Silver
Mercury
Metalloids:Metalloids:
• Zigzag on Periodic Table where metals and nonmetals meet
• Mostly shiny, metallic looking• Only semi-conductive• Often combined with non-metals
Non-Metals:Non-Metals:
•Right side of Periodic Table•Gain or share electrons in a chemical reaction•Dull, not shiny, many are GAS• Do not conduct heat or electricity• Crumble or break if solid
(non-malleable/ductile)
NeonHelium
Iodine Chlorine Carbon Sulfur
Properties of Elements on the Periodic Table An element’s physical and chemical properties
can be predicted from its location in the periodic table Example: Sodium is more reactive than Aluminum
Reactivity in metals decreases as you go from left to right.
For nonmetals, the opposite is true. Nonmetals in Groups 13 through 17 become more reactive from left to right. Group 18, the Noble Gases, are an exception.
• Metals: Orange
• Metalloids: Yellow
• Nonmetals: Purple
• Lanthanide & Actinides: Green
Pre-APPeriodic Trends
• Atomic Radius – related to the atom’s volume.
− Period – atomic radius decreases as you go from left to right
− Group – atomic radius increases as you go down a group
Pre-APPeriodic Trends
• Electronegativity – the atoms “desire” to grab another atom’s electrons.
− Period – electronegativity increases as you go from left to right
− Group – electronegativity decreases as you go down a group
Pre-APPeriodic Trends
• Ionization Energy – amount of energy needed to remove the outermost electron. Closely related to electronegativity.
− Period – Ionization energy increases as you go from left to right
− Group – Ionization energy decreases as you go down a group
Pre-APPeriodic Trends
• Reactivity – how likely or how vigorously an atom is to react with another substance.• Non-Metals
− Period - reactivity increases as you go from left to right, except for Group 18
− Group – reactivity decreases as you go down the group
• Metals − Period – reactivity decreases as you go from left to
right− Group – reactivity increases as you go down a group
Pre-APPeriodic Trends
• Melting Point• Metals – the melting point for metals
decreases as you go down a group• Non-Metals – the melting point for
non-metals increases as you go down a group
Hydrogen Belongs to a family of its own.
Diatomic, reactive gas.
Was involved in the explosion of the Hindenburg aircraft.
Promising as an alternative fuel source for automobiles
Alkali Metals
1st column on the periodic table (Group 1) not including hydrogen.
Very reactive metals
Always combined with something else in nature (like in salt).
Soft enough to cut with a butter knife
1 valence electron
Alkaline Earth Metals Second column on the periodic
table. (Group 2)
Reactive metals
Always combined with nonmetals in nature.
Several are important mineral nutrients (Mg and Ca)
2 valence electrons
Transition Metals
Elements in groups 3-12
Less reactive harder metals
Includes metals used in jewelry and construction.
Boron Family
Elements in group 13
Aluminum metal was once rare and expensive, not a “disposable metal.”
Carbon Family Elements in group 14
Contains elements important to life and computers.
Carbon is the basis for an entire branch of chemistry.
Silicon and Germanium are important semiconductors.
Nitrogen Family Elements in group 15
Nitrogen makes up over ¾ of Earth’s atmosphere.
Nitrogen and phosphorus are both important in living things.
Most of the world’s nitrogen is not available to living things.
The red stuff on the tip of matches is phosphorus.
Oxygen Family Elements in group 16
Oxygen is necessary for respiration.
Many things that stink, contain sulfur (rotten eggs, garlic, skunks,etc.)
Halogens Elements in group 17
Very reactive, volatile, diatomic, nonmetals
Always found combined with other element in nature
Used as disinfectants and to strengthen teeth
The Noble Gases
Elements in group 18
VERY unreactive (STABLE), monatomic gases
Used in lighted “neon” signs
Used in blimps to fix the Hindenburg problem.
Have a full valence shell.
One of two rows that “sits off” to the bottom of the periodic table
Reactive
Fairly soft metals
Lanthanide Series
Also towards bottom of periodic table
All are radioactive, some are not found in nature
Some with higher atomic numbers have only been made in labs
Actinide Series