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Atom
,→About Atoms
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| style="height:20px; width:200px; text-align:center;" |[[Hydrogen]] always has 1 [[proton]].
| style="height:20px; width:200px; text-align:center;" |[[Helium]] always has 2 [[proton]]s.| style="height:20px; width:200px; text-align:center;" |[[Lithium]] always has 3 [[proton]]s.| style="height:20px; width:200px; text-align:center;" |[[Beryllium]] always has 4 [[proton]]s.
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: [[Atom]]s of the same [[element]] can have different numbers of [[neutron]]s so they can be different [[isotope]]s of the same [[element]].
{| class="wikitable"
| style="height:20px; width:200px; text-align:center;" |'''Hydrogen-1'''
| style="height:20px; width:200px; text-align:center;" |'''Hydrogen-2'''
| style="height:20px; width:200px; text-align:center;" |'''Lithium-7'''
| style="height:20px; width:200px; text-align:center;" |'''Lithium-6'''
|-
|[[File:Hydrogen.png|center|200px]]
|[[File:Deuterium.png|center|200px]]
|[[File:Lithium.png|center|200px]]
|[[File:Lithium6.png|center|200px]]
|-
|[[File:HydrogenSymbol.png|center|200px]]
|[[File:DeuteriumSymbol.png|center|200px]]
|[[File:LithiumSymbol.png|center|200px]]
|[[File:Lithium6Symbol.png|center|200px]]
|-
| style="height:20px; width:200px; text-align:center;" |[[Hydrogen]] always has 1 [[proton]] but in this case has no [[neutron]]s.
| style="height:20px; width:200px; text-align:center;" |[[Hydrogen]] always has 1 [[proton]] but in this case also has a [[neutron]]. This [[isotope]] of [[Hydrogen]] is known as [[Deuterium]].
| style="height:20px; width:200px; text-align:center;" |[[Lithium]] always has 3 [[proton]]s but in this case has 4 [[neutron]]s.
| style="height:20px; width:200px; text-align:center;" |[[Lithium]] always has 3 [[proton]]s but in this case has 3 [[neutron]]s. This particular [[isotope]] of [[Lithium]] is [[Unstable Isotope|unstable]] and will [[Radioactive Decay|radioactively decay]].
|}
===History of Atoms===
: The existence and structure of [[atom]]s was not always known.