: The [[Periodic Table]] orders the [[element]]s due to their [[Chemical Property|chemical properties]] but since [[isotope]]s of the same [[element]] have the same [[Chemical Property|chemical properties]] then different [[isotope]]s are not included.
: On the [[Periodic Table]] an [[average]] [[Relative Atomic Mass|atomic mass]] is given based on the [[Relative Atomic Mass|mass]] of each [[isotope]] and how common it is.
: To find the [[Mean Average|average]] [[Relative Atomic Mass|atomic mass]] the [[Relative Atomic Mass|mass]] of each [[isotope]] is considered along with the [[ratio]] of abundance.
====Calculating the Average Relative Atomic Mass====
[[Chlorine]] has two common [[Stable Isotope|stable]] [[Isotope]]s; [[Chlorine-35]] and [[Chlorine-37]]. [[Chlorine-35]] is three times more common than [[Chlorine-37]] so the ratio is 3:1.
To find {| class="wikitable"| style="height:20px; width:300px; text-align:center;" |[[Chlorine]] has two common [[Stable Isotope|stable]] [[Isotope]]s; [[Chlorine-35]] and [[Chlorine-37]]. [[Chlorine-35]] is three times more common than [[Chlorine-37]] so the ratio is 3:1. Find the [[Mean Average|average]] [[Relative Atomic Mass|atomic mass]] of [[Chlorine]].| style="height:20px; width:300px; text-align:center;" |[[Lithium]] has two common [[Stable Isotope|stable]] [[Isotope]]s; [[Lithium-7]] and [[Lithium-6]].92.5% of all [[Lithium]] is the [[isotope]] [[Lithium-7]] while [[Lithium-6]] makes up only 7.5%. Find the [[Mean Average|average]] [[Relative Atomic Mass|atomic mass]] of each [[isotopeLithium]] is considered along with .|-| style="height:20px; width:300px; text-align:left;" |'''1. State the known quantities in [[ratioSI Unit]] of abundances.'''
Ratio: 3:1
3xChlorine-35 : 1xChlorine-37
| style="height:20px; width:300px; text-align:left;" |'''1. State the known quantities in [[SI Unit]]s.'''
Ratio: 92.5:7.5
92.5xLithium-7 : 7.5xLithium-6
|-
| style="height:20px; width:300px; text-align:left;" |'''2. [[Substitute (Maths)|Substitute]] the numbers into the [[equation]] and [[Solve (Maths)|solve]].'''
To find the [[Mean Average|average]]:
: <math>Average=\frac{35+35+35+37}{4}</math>
: <math>Average=\frac{35 \times 3 + 37 \times 1}{4}</math>
: <math>Average=35.5</math>
So the [[Relative Atomic Mass]] of [[Chlorine]] is quoted as <math>Average=\frac{35.5 on the [[Periodic Table]].+35+35+37}{4}</math>
[[Lithium]] has two common [[Stable Isotope|stable]] [[Isotope]]s; [[Lithium-7]] and [[Lithium-6]].92.5% of all [[Lithium]] is the [[isotope]] [[Lithium-7]] while [[Lithium-6]] makes up only 7.5%.<math>Average=\frac{35 \times 3 + 37 \times 1}{4}</math>
Ratio: 92.5:7<math>Average=35.5</math>
92So the [[Relative Atomic Mass]] of [[Chlorine]] is quoted as 35.5xLithium5 on the [[Periodic Table]].| style="height:20px; width:300px; text-7 align: 7left;" |'''2.5xLithium-6[[Substitute (Maths)|Substitute]] the numbers into the [[equation]] and [[Solve (Maths)|solve]].'''
To find the [[Mean Average|average]]:
: <math>Average=\frac{7 \times 92.5 + 6 \times 7.5}{100}</math>: <math>Average=6.925</math>
So the [[Relative Atomic Mass]] of [[Lithium]] is quoted as 6.9, 6.93 or 6.925 depending on the [[precision]] of that particular [[Periodic Table]].
|}