Chapter 2 (atomic structure, isotopes) + Chapter 20 (Nuclear reactions): (remember avogradro's number for Mole -> Grams -> Atoms interconversions)

Question 1

What is a isotope?

Answer 1

• 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

Question 2

Atomic number?

Answer 2

The number of protons in the nucleus of an atom

Question 3

Mass number?

Answer 3

Number of protons + Number of neutrons

Question 4

How to find neutrons from mass number and atomic number?

Answer 4

Subtract mass number from atomic number

Question 5

What is a ion?

Answer 5

An electrically charged atom

Question 6

What is the charge of a proton?

Answer 6

positive

Question 7

What is the charge of a neutron?

Answer 7

neutral

Question 8

What is the charge of an electron?

Answer 8

negative

Question 9

What is a anion?

Answer 9

An atom that gains one or more electrons and exhibits a negative charge

Question 10

What is a cation?

Answer 10

Positively charged atoms that are formed when an atom loses one or more electrons.

Question 11

Where is the atomic number, mass number, and charge of an atom located?

Answer 11

atomic number = bottom left
Mass number = upper left
charge = upper right

Question 12

Alpha decay

Answer 12

NET EFFECT (on the original nuclide): Mass number - 4, Atomic Number - 2
Remember to include He (mass number 4, atomic number 2) in answer

Question 13

Beta decay

Answer 13

NET EFFECT: Mass number = stays same, Atomic Number = +1
Remember to include e -1 in answer

Question 14

Gamma (γ) emission

Answer 14

NET EFFECT: Mass number = 0, Atomic number = 0
Remember to include symbol in equation (γ)

Question 15

Positron emission

Answer 15

NET EFFECT: Mass Number = Stays Same, Atomic Number = Down One
symbol: e +1

Question 16

K-electron capture

Answer 16

NET EFFECT: Mass number = Stays Same, Atomic Number = Down One
symbol: e -1

Question 17

How do you find the number of electrons in an atom (neutral charge)?

Answer 17

Atomic number = number of electrons

Question 18

How do you find the number of electrons in a charged atom?

Answer 18

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

Question 19

How to convert mass (in grams) to moles?

Answer 19

moles = grams/grams/mole
grams/mole = atomic number

Question 20

How to convert from moles to mass (in grams)?

Answer 20

mass = moles x (grams/mole)
grams/mole = atomic number

Question 21

How to find how many atoms/molecules from moles?

Answer 21

moles x 6.022 x 10^23 (avogrado’s number) = molecules

Question 22

How to find how many moles in a molecule?

Answer 22

molecules/6.022 x 10^23 = moles

Question 23

What is a molecular formula?

Answer 23

Molecular formula is the actual formula
of the molecule

Question 24

What is empirical formula?

Answer 24

“simplest” formula of an atom

Question 25

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.

Answer 25

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)

Question 26

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.

Answer 26

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.

Question 27

How to calculate percent composition from mass?

Answer 27

1. Find the molar mass of the entire element
2. Divide the molar mass of each element by the molar mass of the entire element, then multiply by 100 to get the %
3. 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%

Question 28

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?

Answer 28

%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

Question 29

How to figure out which isotope is most abudant given average atomic mass?

Answer 29

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