ISOTOPES Chemistry

Isotope

• Definition: A different form of an element.• Proton number is the same as the other forms or isotopes.• Electron number is the same as the other forms or

isotopes.• Neutron number is DIFFERENT than the other forms or

isotopes.• Different atomic mass (because different # of neutrons!)

• Different isotopes have different characteristics and uses_.

• Some isotopes are found in nature, some are man-made for certain purposes.

Symbols for Isotopes• Isotopes Symbol components• 1. Element symbol• 2. Mass number

(Different for

Different isotopes;

= #P + #N)• 3. #P (same

for each isotope)

Naming isotopes

•How you name an isotope:•Element name – Mass #•Examples: Carbon-14,

Carbon-12,

Carbon-13

Isotope Symbols: Your turn to practice• Write the isotope symbol for each of the following isotopes using

the given information and the information on the previous slides:Isotope Symbol (without help boxes)

• Information• 1. Lithium-4 Or:

• Mass # = #P + #N = 4• Element symbol: Li• #P = 3 (atomic #)

• 2. Lithium-6 Or:• Mass # = #P + #N = 6• Element symbol: Li• #P = 3 (atomic #)

• 3. Lithium-7 Or:• Mass # = #P + #N = 7• Element symbol: Li• #P = 3 (atomic #)

Examples of Isotopes and Uses• Carbon-12 (6P, 6N, 6E)

• Stable in nature• Most abundant isotope of carbon (about 99% of carbon found in nature)• In all carbon-based life (humans, animals, plants), common element in food

– carbohydrates, etc., in ALL living things!

• Carbon-13 (6P, 7N, 6E)• Stable in nature• Common, but less abundant in nature than C-12 (about 1% of carbon found

in nature)

• Carbon-14 (6P, 8N, 6E)• Unstable in nature• Used to data artifacts because it’s radioactive and decays over a certain

amount of time – you can tell how old something is

Isotope Calculations*Some additions made from printout!• Atomic mass of isotope: Grams of 1 mole of that isotope

(Average mass of 1 atom of that isotope)• Percent Abundance of an isotope:

(Mass of a sample of the isotope / Total mass of the entire sample of all isotopes of that element) x100%

(to get the decimal abundance, leave out the “x100%”)• Weighted average atomic mass of the element

• Average atomic mass of the element taking into account the relative abundances of different isotopes of that element

• This is how they calculate the atomic mass of an element on the periodic table of elements!

• Weighted average atomic mass =

(atomic mass for isotope 1) x (decimal abundance for isotope 1) +

(atomic mass for isotope 2) x (decimal abundance for isotope 2) +… (atomic mass for isotope “n”) x (decimal abundance for isotope “n”)