Lesson 1: Atomic Mass and Exponential Decay Flashcards
(35 cards)
Correctly match the following terms with their abbreviation:
I. Mass number
II. Atomic number
III. Number of neutrons
(A) A
(B) M
(C) N
(D) Z
Hydrogen has an atomic number of 1 and an atomic mass of 1. Deuterium has an atomic number of 1 and an atomic mass of 2. How many protons does Hydrogen have compared with Deuterium?
Hydrogen has 1 proton as its atomic number is 1.
Deuterium also has 1 proton as its atomic number is also 1.
What is responsible for the extra mass within Deuterium as compared to Hydrogen?
Deuterium has an extra neutron compared to Hydrogen.
Deuterium and Hydrogen are related in that they are:
(A) Isomers
(B) Isotropes
(C) Isotonic compounds
(D) Isotopes
(D) Isotopes
Isotopes are similar in atomic number but different in terms of their atomic mass, due to differing numbers of neutrons.
An atom with an atomic mass of 161 and 87 neutrons is an isotope of what element? (see periodic table here: https://www.ptable.com/Images/periodic%20table.png)
(A) Francium
(B) Dysporium
(C) Terbium
(D) Tungsten
(D) Tungsten
161 neutrons and protons - 87 neutrons = 74 protons
Consulting the periodic table, the element with 74 protons is Tungsten (W).
Uranium has an atomic number of 92 and an atomic mass of 235. How many neutrons does Uranium contain?
(A) 92
(B) 110
(C) 143
(D) 235
(C) 143
235 neutrons and protons - 92 protons = 143 neutrons
Compare atomic mass and atomic weight.
The atomic mass of an atom is a discrete number based on the number of nucleons in a single atom.
The atomic weight of an element is a weighted average of the atomic masses of all atoms of that element in nature.
Why is the atomic weight of Carbon reported as 12.01 instead of 12?
Because not all Carbon in nature is the Carbon-12 isotope. You have to account for the Carbon-13 that exists out there. The atomic weight is a weighted average
What percent of Carbon atoms out there are Carbon-12 if the atomic weight of Carbon is 12.01?
About 99 percent of Carbon in nature is Carbon 12.
What percentage of Chlorine atoms are Chlorine-35 (34.97 amu) and Chlorine-37 (36.97 amu) if these are the only two isotopes that exist and the atomic weight is 35.45 amu?
(A) 26.58% Chlorine-35; 74.42% Chlorine-37
(B) 50.35% Chlorine-35; 49.65% Chlorine-37
(C) 75.77% Chlorine-35; 24.23% Chlorine-37
(D) 90.21% Chlorine-35; 9.79% Chlorine-37
(C) 75.77% Chlorine-35; 24.23% Chlorine-37
34.97(x) + 36.97 (1-x) = 35.45
2x = 1.52 x = 0.76 = 76%
Approximately 75% of the chlorine is Chlorine-35 and 25% is Chlorine-37.
What accounts for the actual mass of Helium being .03 amu less than its predicted mass (the mass expected based on the individual masses of its protons, neutrons and electrons)?
The .03 amu is a result of the mass being converted into energy as the protons, neutrons, and electrons are brought together to form the atom.
The actual mass of Helium is .03 amu less than its predicted mass (the mass expected based on the individual masses of its protons, neutrons and electrons). In the case of Helium, .03 amu is considered the:
(A) Binding energy
(B) Atomic mass
(C) Atomic mass difference
(D) Mass defect
(D) Mass defect
The mass defect is the mass difference between the actual and predicted mass of an atom.
What equation for energy equates a change in mass to a change in energy?
E= mc^2
E = Energy m = mass c = speed of light = 3⋅10^8 m/s
If there is a 0.03 amu mass defect of Helium, there are 1.66054 ⋅ 10^-27 kg per amu, and the speed of light is 2.99792 ⋅ 10^8, what is the binding energy for Helium?
(A) 1.2 ⋅ 10^-6 J
(B) 5.8 ⋅ 10^-9 J
(C) 4.5 ⋅ 10^-12 J
(D) 9.4 ⋅ 10^-14 J
(C) 4.5 ⋅ 10^-12 J
(.03 amu )⋅(1.66054 ⋅ 10^-27 kg/amu) = 5 ⋅ 10^-29 kg
E = mc^2 E = (5 ⋅ 10^-29)((3 ⋅ 10^8)^2) E = 4.5 ⋅ 10^-12 J
What is Avogadro’s number equal to, and how does it relate the number of atoms of an element to moles?
Avogadro’s number (NA)= 6.02 ⋅ 10^23 mol^-1
Avogadro’s number is the number of atoms/molecules in a mole, so multiplying Avogadro’s number by the moles of an element gives the number of atoms of that element.
If the atomic weight of Xenon is 131.3, how much does 10^22 atoms of Xenon weigh in grams?
(A) 1.31 g
(B) 2.18 g
(C) 4.97 g
(D) 11.31 g
(B) 2.18 g
10^22/(6.02 ⋅ 10^23 mol^-1) = approx 1.5 ⋅ 10^-2 mol (actual 0.0166 mol Xenon)
0.0166mol ⋅ 131.3 g/mol = approximately 2.5g Xenon (actual 2.18g Xenon)
The nuclear strong force accounts for what phenomenon?
The nuclear strong force accounts for the fact that the protons in the nucleus are both positively charged and yet are not repelling each other.
Which of the following are considered nucleons?
I. Protons
II. Neutrons
III. Electrons
(A) I Only
(B) I and II Only
(C) II and III Only
(D) I, II, and III
(B) I and II Only
Protons and neutrons are both considered nucleons as they are both found in the nucleus of an atom.
When describing the mass number of an atom, the units used are __________. One of these units can describe the mass of ____________.
(A) amu, protons
(B) amu, neutrons
(C) amu, nucleons
(D) grams, neutrons
(C) amu, nucleons
When describing the mass number of an atom, the units used are atomic mass units (amu). One of these units can describe the mass of nucleons (both protons and neutrons).
True or false? Although not a nucleon, an electron’s mass is also approximately 1 amu.
False. An electron’s mass is about 1/2000th of an amu, making it significantly less massive than a nucleon.
Which is stronger? The electrostatic force between the protons in a nucleus, or the nuclear strong force?
The nuclear strong force, which is why the protons are not repelled away from each other.
Which only acts over short distances? The electrostatic force between the protons in a nucleus, or the nuclear strong force?
The nuclear strong force only acts over short distances.
The N/Z ratio of Carbon-14 is 4/3. What does this indicate concerning the stability of Carbon-14?
It is unstable and will undergo radioactive decay.
The stable N/Z ratio for large atoms (Z > 83) is greater or less than that of small atoms? Why?
The stable N/Z ratio for large atoms is greater than that of small atoms. This is due to the fact that once you add more nucleons to a nucleus, the protons on opposite ends of the nucleus will not experience the strong nuclear force; thus, protons will be more repelled from one another, resulting in less protons per neutrons in the nucleus.
