Page 202 - Science Course 1 (Book 1)

Mo6-L2a: How do Atoms Differ?

The mass number of an atom is the sum of the
number of protons and neutrons in an atom.
e Mass number = number of protons + number of
e neutrons
Carbon - 13
n e e 6 An isotope is often written with the element name
p p followed by the mass number.
e n 7 Carbon - 12

e p 6 e e e 6

e e n 6
n

e p p p 6

e e 12
e C 6
Carbon - 14 e
n e e 6
p p e Carbon - 13
e n 8 e e 6

e p 6 n n 7
e p p
e e p 6
e
13
e C 6

Naturally Occurring Isotopes of Carbon

Isotopes Carbon - 12 Nucleus Carbon - 13 Nucleus Carbon - 14 Nucleus

Abundance 98.89% <1.11% <0.01%

Protons 6 6 6

Neutrons +6 +7 +8

Mass Number 12 13 14

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