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Isotopes
Isotopes are:Different forms of the same element
with the SAME # of Protons but with DIFFERENT #’s of Neutrons
Mass Number
Mass Number = Total Protons + Neutrons in an isotope of an element
3HMass Number
P + N
1 P + 2 N’s
Also called “Hydrogen – 3”
Practice Problem To find P’s and N’s from Nuclear
Notation
Calcium’s atomicNumber = 20
20 Protons
To find # ofNeutrons, putAtomic NumberHere:
Mass # = P + N
Subtract to get #of Neutrons
21
So it has 21 Neutrons
41Ca20
Ion
An ion is an atom where:# of e-’s ¹ ≠ # of p’s
In a + ion (cation)# of e-’s < # of p’s
In a - ion (anion)# of e-’s > # of p’s
Example #1
The ion Ca 2+
has 20 protons (atomic #) and it has 18 e-’s (2 less –’s than +’s, hence a 2+ charge)
Example 2
The ion Se 2-has 34 protons (atomic #) and it has 36 e-’s (2 more –’s than +’s, hence a 2- charge)
Example 3
An atom of Bi has 83 protons (atomic #) and it has 83 e-’s (e-’s are equal to protons, hence, no charge (neutral))
Finding (average) atomic mass using isotope abundances
Assumption: Assume mass of a neutron = mass of proton =
1 u (atomic mass unit) this is not “exactly” correct
The mass of a proton = 1.007276 uThe mass of a neutron = 1.00866 u