Isotopes. Of the Atom. Isotopes At the conclusion of our time together, you should be able to:. Define an isotope Determine the number of protons, neutrons and electrons for an isotope Define average atomic mass Determine the average atomic mass for an element given the isotopes.
Of the Atom
Atoms with the same number of protons & electrons but a different number of neutrons.
They are the same element, are chemically identical and undergo the exact same chemical reactions
They have different masses (different mass number).
All isotopes are used to calculate average atomic mass (this mass is usually a decimal).
Most elements consist of a mixture of isotopes.
Hint #12. The probability of a given event occurring is inversely proportional to its desirability.
Because of the existence of isotopes, the mass of a collection of atoms has an average value.
Boron is 20%10B and 80%11B. That is, 11B makes up 80% of the boron in the earth’s crust.
For boron average atomic mass
= 0.20 (10 amu) + 0.80 (11 amu) = 10.8 amu
Determine Relative Abundance –
% abundance divided by 100
Determine mass of each isotope and multiply relative abundance by this mass
(keep all digits your calculator gives you)
Determine Average Atomic Mass by adding up all the individual masses, round to “2” decimal places
Avg. Atomic mass of N = ______________
Avg. Atomic mass of Sb = ______________
There are three naturally occurring isotopes of neon: Ne-20, 90.51%, 19.99244 amu;
Ne-21, 0.27%, 20.99395 amu;
Ne-22, 9.22%, 21.99138 amu. Calculate the average atomic mass of neon.
Atomic mass = (0.9051 x 19.99244 amu)
+ (0.0027 x 20.99395 amu) +
(0.0922 x 21.99138 amu)
Atomic mass = 18.10 amu + 0.057 amu
+ 2.03 amu =
Get your clickers ready!!!
Which of the following represent isotopes of the same element?
234 X234 X235 X238 X
Naturally occurring carbon consists of three isotopes, 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of these carbon atoms.
12C 13C 14C
6 6 6
#p+ _______ _______ _______
#no _______ _______ _______
#e- _______ _______ _______
An atom has 14 protons and 20 neutrons.
A. Its atomic number is
a) 14 b) 6 c) 34 d) 20
B. Its mass number is
a) 14 b)20 c) 16 d) 34
C. The element is
a) Si b) Ca c) Se d) C
D. Another isotope of this element is
a) 34X b) 34X c) 36X
16 14 14
Silicon has 3 isotopes with the following % abundances.
Calculate silicon’s average atomic mass.
(28 amu x 0.9223) + (29 amu x 0.0467) + (30 amu x .031)
= 28.11 amu
Element “X” has three naturally occurring isotopes. 78.70% of “X” atoms exist as X-24, 10.03% exist as X-25 and 11.17% exist as X-26. What is the average atomic mass of element “X” in amu’s?