Chapter 2 (atomic structure, isotopes) + Chapter 20 (Nuclear reactions): (remember avogradro's number for Mole -> Grams -> Atoms interconversions) Flashcards
What is a isotope?
- atoms of the same element that differ in mass.
- The atomic number is the same, but there’s a different number of neutrons, which changes the mass number
- CHANGE IN ELECTRONS = NOT AN ISOTOPE
Atomic number?
The number of protons in the nucleus of an atom
Mass number?
Number of protons + Number of neutrons
How to find neutrons from mass number and atomic number?
Subtract mass number from atomic number
What is a ion?
An electrically charged atom
What is the charge of a proton?
positive
What is the charge of a neutron?
neutral
What is the charge of an electron?
negative
What is a anion?
An atom that gains one or more electrons and exhibits a negative charge
What is a cation?
Positively charged atoms that are formed when an atom loses one or more electrons.
Where is the atomic number, mass number, and charge of an atom located?
atomic number = bottom left
Mass number = upper left
charge = upper right
Alpha decay
NET EFFECT (on the original nuclide): Mass number - 4, Atomic Number - 2
Remember to include He (mass number 4, atomic number 2) in answer
Beta decay
NET EFFECT: Mass number = stays same, Atomic Number = +1
Remember to include e -1 in answer
Gamma (γ) emission
NET EFFECT: Mass number = 0, Atomic number = 0
Remember to include symbol in equation (γ)
Positron emission
NET EFFECT: Mass Number = Stays Same, Atomic Number = Down One
symbol: e +1
K-electron capture
NET EFFECT: Mass number = Stays Same, Atomic Number = Down One
symbol: e -1
How do you find the number of electrons in an atom (neutral charge)?
Atomic number = number of electrons
How do you find the number of electrons in a charged atom?
Positive charge = subtract charge number from atomic number
EX: Boron-6 e+1 = 5 electrons
Negative charge = add charge number to atomic number
EX: Boron-6 e-1 = 7 electrons
How to convert mass (in grams) to moles?
moles = grams/grams/mole
grams/mole = atomic number
How to convert from moles to mass (in grams)?
mass = moles x (grams/mole)
grams/mole = atomic number
How to find how many atoms/molecules from moles?
moles x 6.022 x 10^23 (avogrado’s number) = molecules
How to find how many moles in a molecule?
molecules/6.022 x 10^23 = moles
What is a molecular formula?
Molecular formula is the actual formula
of the molecule
What is empirical formula?
“simplest” formula of an atom
How to calculate mass of an element from % isotope abundance?
Example problem: Boron consists of 2 isotopes which occur naturally, 11B and 10B. Compute the atomic mass of naturally occuring boron given % abundance.
Create a table, then find mass contribution by multiplying AMU by % abundance. Then, add both mass contributions together for mass of element.
Remember this formula:
Average amu = M1P1 + M2P2
EXAMPLE:
Isotope: 10 B
At.Mass (amu): 10.012935
% abundance: 18.83%
Mass contribution: 1.885 amu
Isotope: 11 B
At. Mass (amu): 11.009305
% abundance: 81.17%
Mass contribution: 8.936 amu
1.885 + 8.936 amu = 10.821 amu (mass of natural element)
How to calculate mass of an isotope given:
- % abundance of only 1 isotope
- mass of both isotopes
- mass contribution
EX: Silver has 2 naturally occuring isotopes: silver-107 and silver-109. 107 Ag has a mass of 106.905 + %abundance of 51.82%. Naturally occuring silver has a mass of 107.868. Calculate mass of 109 Ag.
First, find the % abundance of 109 Ag by subtracting 51.82% from 100% (48.18%).
Then, find mass contribution of 107 Ag by multiplying 51.82% by 106.905 amu (55.40 amu).
Then, subtract 55.40 amu from 107.868 to get the mass contribution of 109 Ag (52.47 amu)
Lastly, divide 52.47 amu by 48.18% to get a mass of 108.90 amu.
How to calculate percent composition from mass?
- Find the molar mass of the entire element
- Divide the molar mass of each element by the molar mass of the entire element, then multiply by 100 to get the %
- Check your work by making sure all percents add up to 100%
EX: C5H9NO2
Step 1:
5C + 9H + N + 2O
5 (12.01) + 9(1.008) + N(14.01) + 2 (16.000)
= 60.05 + 9.072 + 14.01 + 32
total molar mass of element = 115.132 g/mol
Step 2:
%C = 60.05/115.132 * 100 = 52.16%
%H = 9.072/115.132 *100 = 7.88%
%N = 14.01/115.132 * 100 = 12.17%
%O = 32/115.132 *100 = 27.79%
Step 3:
52.16% + 7.88% + 12.17% + 27.79% = 100%
Example problem: A molecule contains a single atom of Nitrogen. If the mass % of Nitrogen in this compound is 13.32% what is the molar mass of the molecule?
%N = mass N / molar mass * 100%
13.32% = 1(14.01)/X * 100
0.1332 = 14.01/x
14.01 = 0.1332x
x = 105.18 g/mol
How to figure out which isotope is most abudant given average atomic mass?
Look at the isotopes. Whichever number is closest to the average amu is most abundant
EX: Mg - 24, Mg - 25, and Mg - 26.
Average amu = 24.305
Which is most abundant?
Ans = Mg-24
- this is the closest number to 24.305
