periodic table
hydrogen
helium
boron
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Periodic Table first discovered in 1869 by Dmitry I. Mendeleyev is a way of presenting all the elements so as to show their similarities and differences. The elements are arranged in increasing order of atomic number(Z) as you go from left to right accross the table. The horizontal rows a called periods and the vertical rows, groups.
A noble gas is found at the right hand side of each period. There is a progression from metals to non-metals across each period. Elements found in groups (e.g. alkali, halogens) have a similar electronic configuration. The number of electrons in outer shell is the same as the number of the group (e.g. lithium 2ยท1).
The block of elements between groups II and III are called transition metals. These are similar in many ways; they produce colored compounds, have variable valency and are often used as catalysts. Elements 58 to 71 are known as lanthanide or rare earth elements. These elements are found on earth in only very small amounts.
Elements 90 to 103 are known as the actinide elements. They include most of the will known elements which are found in nuclear reactions. The elements with larger atomic numbers than 92 do not occur naturally. They have all been produced artificially by bombarding other elements with particles.

* Name: hydrogen
* Symbol: H
* Atomic number: 1
* Atomic weight: 1.00794 (7)

* Group in periodic table: 1
* Group name: (none). While normally shown at the top of the Group 1 elements in the periodic table, the term "alkaline metal" refers only to Group 1 elements from lithium onwards.
* Period in periodic table: 1
* Block in periodic table: s-block

* Name: helium
* Symbol: He
* Atomic number: 2
* Atomic weight: 4.002602 (2)

* Group in periodic table: 18
* Group name: Noble gas
* Period in periodic table: 1
* Block in periodic table: p-block

* Name: boron
* Symbol: B
* Atomic number: 5
* Atomic weight: 10.811 (7) g m r
* CAS Registry ID: 7440-42-8

* Group number: 13
* Group name: (none)
* Period number: 2
* Block: p-block

beryllium
* Name: beryllium
* Symbol: Be
* Atomic number: 4
* Atomic weight: 9.012182 (3)

* Group in periodic table: 2
* Group name: Alkaline earth metal
* Period in periodic table: 2
* Block in periodic table: s-block

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lithium
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* Name: lithium
* Symbol: Li
* Atomic number: 3
* Atomic weight: [ 6.941 (2)] g m r
* CAS Registry ID: 7439-93-2

* Group number: 1
* Group name: Alkali metal
* Period number: 2
* Block: s-block

sodium
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* Name: sodium
* Symbol: Na
* Atomic number: 11
* Atomic weight: 22.98976928 (2)

* Group in periodic table: 1
* Group name: Alkali metal
* Period in periodic table: 3
* Block in periodic table: s-block

carbon
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* Name: carbon
* Symbol: C
* Atomic number: 6
* Atomic weight: 12.0107 (8) g r
* CAS Registry ID: 7440-44-0

* Group number: 14
* Group name: (none)
* Period number: 2
* Block: p-block

nitrogen
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* Name: nitrogen
* Symbol: N
* Atomic number: 7
* Atomic weight: 14.0067 (2) g r
* CAS Registry ID: 7727-37-9

* Group number: 15
* Group name: Pnictogen
* Period number: 2
* Block: p-block

oxygen
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* Name: oxygen
* Symbol: O
* Atomic number: 8
* Atomic weight: 15.9994 (3) g r
* CAS Registry ID: 7782-44-7

* Group number: 16
* Group name: Chalcogen
* Period number: 2
* Block: p-block

fluorine
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* Name: fluorine
* Symbol: F
* Atomic number: 9
* Atomic weight: 18.9984032 (5)
* CAS Registry ID: 7782-41-4

* Group number: 17
* Group name: Halogen
* Period number: 2
* Block: p-block

neon
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* Name: neon
* Symbol: Ne
* Atomic number: 10
* Atomic weight: 20.1797 (6) g m
* CAS Registry ID: 7440-01-9

* Group number: 18
* Group name: Noble gas
* Period number: 2
* Block: p-block

magnesium
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* Name: magnesium
* Symbol: Mg
* Atomic number: 12
* Atomic weight: 24.3050 (6)
* CAS Registry ID: 7439-95-4

* Group number: 2
* Group name: Alkaline earth metal
* Period number: 3
* Block: s-block

aluminium
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* Name: aluminium
* Symbol: Al
* Atomic number: 13
* Atomic weight: 26.9815386 (8)
* CAS Registry ID: 7429-90-5

* Group number: 13
* Group name: (none)
* Period number: 3
* Block: p-block

silicon
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* Name: silicon
* Symbol: Si
* Atomic number: 14
* Atomic weight: 28.0855 (3) r
* CAS Registry ID: 7440-21-3

* Group number: 14
* Group name: (none)
* Period number: 3
* Block: p-block

phosphorus
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* Name: phosphorus
* Symbol: P
* Atomic number: 15
* Atomic weight: 30.973762 (2)
* CAS Registry ID: 7723-14-0

* Group number: 15
* Group name: Pnictogen
* Period number: 3
* Block: p-block

sulfur
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* Name: sulfur
* Symbol: S
* Atomic number: 16
* Atomic weight: 32.065 (5) g r
* CAS Registry ID: 7704-34-9

* Group number: 16
* Group name: Chalcogen
* Period number: 3
* Block: p-block

chlorine
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* Name: chlorine
* Symbol: Cl
* Atomic number: 17
* Atomic weight: 35.453 (2) g m
* CAS Registry ID: 7782-50-5

* Group number: 17
* Group name: Halogen
* Period number: 3
* Block: p-block

argon
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* Name: argon
* Symbol: Ar
* Atomic number: 18
* Atomic weight: 39.948 (1) g r
* CAS Registry ID: 7440-37-1

* Group number: 18
* Group name: Noble gas
* Period number: 3
* Block: p-block

potassium
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* Name: potassium
* Symbol: K
* Atomic number: 19
* Atomic weight: 39.0983 (1)
* CAS Registry ID: 7440-09-7

* Group number: 1
* Group name: Alkali metal
* Period number: 4
* Block: s-block

calcium
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* Name: calcium
* Symbol: Ca
* Atomic number: 20
* Atomic weight: 40.078 (4) g
* CAS Registry ID: 7440-70-2

* Group number: 2
* Group name: Alkaline earth metal
* Period number: 4
* Block: s-block

scandium
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* Name: scandium
* Symbol: Sc
* Atomic number: 21
* Atomic weight: 44.955912 (6)
* CAS Registry ID: 7440-20-2

* Group number: 3
* Group name: (none)
* Period number: 4
* Block: d-block

titanium
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* Name: titanium
* Symbol: Ti
* Atomic number: 22
* Atomic weight: 47.867 (1)
* CAS Registry ID: 7440-32-6

* Group number: 4
* Group name: (none)
* Period number: 4
* Block: d-block

vanadium
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* Name: vanadium
* Symbol: V
* Atomic number: 23
* Atomic weight: 50.9415 (1)
* CAS Registry ID: 7440-62-2

* Group number: 5
* Group name: (none)
* Period number: 4
* Block: d-block

chromium
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* Name: chromium
* Symbol: Cr
* Atomic number: 24
* Atomic weight: 51.9961 (6)
* CAS Registry ID: 7440-47-3

* Group number: 6
* Group name: (none)
* Period number: 4
* Block: d-block

manganese
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* Name: manganese
* Symbol: Mn
* Atomic number: 25
* Atomic weight: 54.938045 (5)
* CAS Registry ID: 7439-96-5

* Group number: 7
* Group name: (none)
* Period number: 4
* Block: d-block

iron
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* Name: iron
* Symbol: Fe
* Atomic number: 26
* Atomic weight: 55.845 (2)
* CAS Registry ID: 7439-89-6

* Group number: 8
* Group name: (none)
* Period number: 4
* Block: d-block

cobalt
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* Name: cobalt
* Symbol: Co
* Atomic number: 27
* Atomic weight: 58.933195 (5)
* CAS Registry ID: 7440-48-4

* Group number: 9
* Group name: (none)
* Period number: 4
* Block: d-block

nickel
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* Name: nickel
* Symbol: Ni
* Atomic number: 28
* Atomic weight: 58.6934 (2)
* CAS Registry ID: 7440-02-0

* Group number: 10
* Group name: (none)
* Period number: 4
* Block: d-block

copper
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* Name: copper
* Symbol: Cu
* Atomic number: 29
* Atomic weight: 63.546 (3) r
* CAS Registry ID: 7440-50-8

* Group number: 11
* Group name: Coinage metal
* Period number: 4
* Block: d-block

zinc
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* Name: zinc
* Symbol: Zn
* Atomic number: 30
* Atomic weight: 65.409 (4) g
* CAS Registry ID: 7440-66-6

* Group number: 12
* Group name: (none)
* Period number: 4
* Block: d-block

gallium
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* Name: gallium
* Symbol: Ga
* Atomic number: 31
* Atomic weight: 69.723 (1)
* CAS Registry ID: 7440-55-3

* Group number: 13
* Group name: (none)
* Period number: 4
* Block: p-block

germanium
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* Name: germanium
* Symbol: Ge
* Atomic number: 32
* Atomic weight: 72.64 (1)
* CAS Registry ID: 7440-56-4

* Group number: 14
* Group name: (none)
* Period number: 4
* Block: p-block

arsenic
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* Name: arsenic
* Symbol: As
* Atomic number: 33
* Atomic weight: 74.92160 (2)
* CAS Registry ID: 7440-38-2

* Group number: 15
* Group name: Pnictogen
* Period number: 4
* Block: p-block

selenium
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* Name: selenium
* Symbol: Se
* Atomic number: 34
* Atomic weight: 78.96 (3)
* CAS Registry ID: 7782-49-2

* Group number: 16
* Group name: Chalcogen
* Period number: 4
* Block: p-block

bromine
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* Name: bromine
* Symbol: Br
* Atomic number: 35
* Atomic weight: 79.904 (1)
* CAS Registry ID: 7726-95-6

* Group number: 17
* Group name: Halogen
* Period number: 4
* Block: p-block

krypton
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* Name: krypton
* Symbol: Kr
* Atomic number: 36
* Atomic weight: 83.798 (2) g m
* CAS Registry ID: 7439-90-9

* Group number: 18
* Group name: Noble gas
* Period number: 4
* Block: p-block

rubidium
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* Name: rubidium
* Symbol: Rb
* Atomic number: 37
* Atomic weight: 85.4678 (3) g
* CAS Registry ID: 7440-17-7

* Group number: 1
* Group name: Alkali metal
* Period number: 5
* Block: s-block

strontium
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* Name: strontium
* Symbol: Sr
* Atomic number: 38
* Atomic weight: 87.62 (1) g r
* CAS Registry ID: 7440-24-6

* Group number: 2
* Group name: Alkaline earth metal
* Period number: 5
* Block: s-block

yttrium
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* Name: yttrium
* Symbol: Y
* Atomic number: 39
* Atomic weight: 88.90585 (2)
* CAS Registry ID: 7440-65-5

* Group number: 3
* Group name: (none)
* Period number: 5
* Block: d-block

zirconium
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* Name: zirconium
* Symbol: Zr
* Atomic number: 40
* Atomic weight: 91.224 (2)
* CAS Registry ID: 7440-67-7

* Group number: 4
* Group name: (none)
* Period number: 5
* Block: d-block

niobium
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* Name: niobium
* Symbol: Nb
* Atomic number: 41
* Atomic weight: 92.90638 (2)
* CAS Registry ID: 7440-03-1

* Group number: 5
* Group name: (none)
* Period number: 5
* Block: d-block

Click on an element symbol and see a detailed description of that element and how it relates to water treatment