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Periodic Table Arrangement
(Periods and Groups)Ā
The periodic table of elements is how scientists organize the known elements. This includes non metals, metals, and metalloids. These elements are the fundamental building blocks of all matter
Periods and Groups:Ā
What are periods?Ā Ā Ā Ā Ā Ā Ā
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Ā Ā Ā Ā Ā Ā Ā Ā Periods are the horizontal rows of elements
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Periods are arranged in order of increasing atomic number. Atomic number is the number of protons in one atom of the given element. The atomic number of Fe, or Iron is 26.
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Moving from left to right, you can observe that the atomic number of each element is increasing by one.
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What happens in periods?
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An increasing atomic number might make it seem as if the atoms are growing bigger, but they are doing the opposite.Ā In chemistry, opposites attract. This means that something with a negative charge will be attracted to something with a positive charged.Ā
Protons (positive charge) in the nucleus and electrons (negative charge) in the shells will be attracted to each other. This is called force of attraction. When there are more protons are more electrons, the force of attraction grows stronger. The electrons in the outer shells of the atom will be pulled in towards the nucleus which makes the atom smaller. The atomic radius decreases when moving across a period.
Periodic table by 2012rc, CC BY 3.0, via Wikimedia Commons
What are groups?Ā Ā Ā Ā Ā Ā Ā
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Ā Ā Ā Ā Ā Ā Ā Ā Groups are the vertical columns of elements
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Groups are arranged by increasing number of shells. The number of shells an element has is equal to its period number. For example, an atom of sodium (Na) has three shells and is in the third period.
When moving from top to bottom in a group, each element has one more shell than the element above it. Elements in the same group will all have the same number of valence electrons.
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What happens in groups?Ā Ā Ā Ā Ā Ā Ā
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When we move down in a group, the atom of the element will increase. This is because each element has one more shell than the last. The more shells an element has, the bigger it will be. Therefore the atomic radius increases when moving down a group
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Categories:Ā
Periodic tables are often color coded to show the different categories/families of elements.
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Periodic table by 2012rc, CC BY 3.0, via Wikimedia Commons
Alkali metals (red):Ā Elements in the first group except for hydrogen. These are soft metals which each have one valence electron. This explains why they are grouped together. Their one valence electron causes them to be highly reactive as they are eager to lose their electron. These metals are never found alone in nature and are always bonded to another element.
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Alkaline earth metals (beige):Ā Elements in the second group. These metals each have two valence electrons making them slightly less reactive as alkali metals. These are harder and have higher melting points than alkali metals but are soft in comparison to other metals.
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Transition metals (peach):Ā Elements in groups 3-12. Transition metals are the largest category on the table. These elements are what you might think of as typical metals. They are shiny, malleable meaning they can be hammered into shapes, and ductile meaning they can be made in to wires and are good conductors of electricity. They are less reactive and have higher melting points than alkali metals and alkaline earth metals.
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Halogens (not shown):Ā Elements in the 17th group. Each element has seven valence electrons causing them to be highly reactive as they are eager to gain one electron. When in their pure form, all of these elements are extremely toxic and dangerous.
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Noble Gases (blue):Ā Elements in the 18th group. These elements have a complete outer shell making them fully stable and unreactive. They rarely form bonds with other elements and have low boiling and melting points.
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Lanthanides/actinides:Ā Elements in the two rows beneath the main table. These are all soft, shiny and reactive metals. These elements are their own category for two reasons. 1 - to keep the arrangement of the periodic table neat. 2 - the electrons in these elements fill a different shell which you will learn more about when studying electron shells.
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- Periods are horizontal rowsĀ
- Groups are vertical columns
- Atomic radius decreases in periods and increases in groups
- There are several families/categories within the table
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Summary:Ā