Atomic Structure
Which subatomic particle determines the atomic number of an element?
An atom has the same number of protons and electrons. Is it neutral or an ion?
neutral
An element has two isotopes:
X-20 = 80%
X-22 = 20%
Would its average atomic mass be closer to 20 amu or 22 amu?
20 amu
Which type of radiation is represented by α?
alpha particle
What subatomic particle helps provide stability to the nucleus
neutron
A radioactive isotope has a half-life of 4 hours. If you start with 80 g, how much remains after 4 hours?
40 g
An atom has 17 protons and 18 electrons. What is its charge
1−
Two atoms have the same number of protons but different numbers of neutrons. What are they called?
isotopes
Element X has two isotopes:
X-10 = 25%
X-11 = 75%
Which isotope contributes more to the element's average atomic mass?
X-11
What is the charge of a beta particle?
−1
When balancing a nuclear equation, what two numbers must be conserved on both sides?
mass number and atomic number
A sample begins with 100 g of a radioactive isotope. After 2 half-lives, how much of the sample remains?
25 g
An atom has 24 protons, 21 electrons, and 28 neutrons. Determine its:
A neutral fluorine atom gains one electron. What happens to its charge?
it becomes a 1− ion
An element has the following isotopes:
Isotope Mass & % Abundance
24.0 amu, 60%
25.0 amu, 30%
26.0 amu, 10%
Calculate its average atomic mass.
24.5 amu
Which of these has no charge?
Alpha
Beta
Gamma
gamma radiation
Complete the nuclear equation:
¹⁴₆C → ¹⁴₇N + _____
⁰₋₁e (beta particle)
A radioactive isotope has a half-life of 3 years. If you start with 160 g, how much remains after 9 years?
20 g
An ion has a mass number of 39, 19 protons, and a 1+ charge. How many electrons and neutrons does it have?
18 electrons and 20 neutrons
Compare F and F⁻. What is different between these two atoms? Be Specific!
their number of electrons and their charge
F has 9 electrons and is neutral.
F⁻ has 10 electrons and a 1− charge.
An element has three isotopes:
Isotope Mass & % Abundance
27.98 amu, 92%
28.98 amu, 5%
29.97 amu, 3%
Without calculating, which isotope mass should the average atomic mass be closest to? Explain why.
27.98 amu, because it has by far the greatest relative abundance
Put these three types of radiation in order from least penetrating to most penetrating:
Gamma, Alpha, Beta
Alpha < Beta < Gamma
Complete the nuclear equation:
²³⁸₉₂U → ²³⁴₉₀Th + _____
⁴₂He (an alpha particle)
A radioactive sample has gone through 3 half-lives.
What percentage of the original sample decayed?
87.5%
An unknown atom has 36 electrons, 44 neutrons, and a 1− charge. Identify the element and determine its atomic number and mass number.
bromine (Br), atomic number 35, mass number 79
Particle A has 12 protons, 12 neutrons, and 12 electrons.
Particle B has 12 protons, 13 neutrons, and 10 electrons.
Give two ways these particles differ.
An element has two main isotopes: X-10 and X-11. Its average atomic mass is 10.81 amu.
Which isotope is more abundant, and how can you tell?
X-11
The average atomic mass of 10.81 amu is much closer to 11 than to 10, indicating that X-11 is more abundant.
Identify the type of radiation:
alpha particle
Complete the nuclear equation and identify the type of radiation emitted:
²¹⁰₈₄Po → _____ + ⁴₂He
²⁰⁶₈₂Pb; alpha radiation
A radioactive isotope has a half-life of 5 hours. A sample originally contains 320 mg, but only 20 mg remains.
How many half-lives have passed, and how much time has passed?
4 half-lives and 20 hours
An unknown ion has 3 more protons than electrons, 42 neutrons, and a mass number of 73.
Determine:
31 protons, 28 electrons, atomic number 31, a 3+ charge, and gallium (Ga)
Three particles have the following properties:
Particle A: mass number 58, 23 electrons, 30 neutrons
Particle B: mass number 72, charge 2+, 26 electrons
Particle C: mass number 58, 25 electrons, charge 2+
Which two are the same element?
A and B both have 28 protons/atomic number and are isotopes because they have different mass numbers
A mystery element has three naturally occurring isotopes:
mass & percent:
23.985 amu, 78.7%
24.986 amu, ?%
25.983 amu, 10.9%
What is the missing precent and the average atomic mass?
10.4% and 24.31 amu
Three unknown forms of radiation have the following properties:
Identify A, B, and C, and give the symbol for each.
A radioactive parent isotope undergoes alpha emission and produces ²²²₈₆Rn.
Determine:
parent: radium-226 (²²⁶₈₈Ra)?
atomic #: 88
mass #: 226
²²⁶₈₈Ra → ²²²₈₆Rn + ⁴₂He
A radioactive isotope has a half-life of 6 hours. After 24 hours, a sample has 15 mg remaining.
Determine:
4 half-lives, 240 mg originally, 1/16 remaining, 6.25% remaining, and 93.75% decayed