2A1 Atomic and Nuclear Structure and Processes Flashcards
Explain the current model of atomic structure. Describe the characteristics, processes, and effects of radioactivity.
Define:
Atom
The smallest unit of matter.
Atoms are the basic building blocks of all elements and compounds.
Which three subatomic particles make up an atom?
- Protons
- Neutrons
- Electrons
Protons and neutrons are located in the nucleus, while electrons orbit around the nucleus.
What is the charge of a proton?
Positive (+)
Protons carry a positive electrical charge, opposite to the negative charge of electrons.
Where are protons located in an atom?
In the nucleus.
Protons, along with neutrons, make up the nucleus of an atom, contributing most of the atom’s mass.
Where are electrons located in an atom?
Outside the nucleus, in electron shells.
Electrons move around the nucleus in specific energy levels or orbitals.
Fill in the blank:
The atomic number of an element is the number of ________.
protons
The atomic number determines the identity of an element, as all atoms of a given element have the same number of protons.
Fill in the blank:
The mass number of an atom is represented by the letter _____.
A
The mass number is the sum of protons and neutrons and is represented by the letter A in element notation.
Fill in the blank:
Mass number = ________ + ________.
Protons, Neutrons
The mass number is the sum of protons and neutrons and is often represented by the symbol “A”.
Define:
Isotope
Atoms of the same element with different numbers of neutrons.
Isotopes have the same chemical properties but differ in mass due to the varying number of neutrons. Examples include Carbon-12 or Hydrogen-2.
What is the difference between an isotope and an ion?
Isotopes differ in neutrons, while ions differ in electrons.
Isotopes are atoms of the same element with different numbers of neutrons; ions are atoms with a net charge due to the loss or gain of electrons.
True or False:
An element is a substance made up of only one type of atom.
True
Elements are pure substances consisting of atoms with the same number of protons. Examples include oxygen or carbon.
True or False:
Mass number and atomic mass are the same.
False
Mass number is the total of protons and neutrons in a nucleus, while atomic mass is the weighted average of all naturally occurring isotopes.
Who discovered the nucleus of the atom in 1909?
Ernest Rutherford
Rutherford’s gold foil experiment revealed that atoms have a dense central nucleus.
What is the mass of an electron?
Nearly 0 atomic mass units.
Electrons are so light compared to protons and neutrons that their mass is considered negligible in most calculations.
Define:
atomic orbitals
Regions around the nucleus where electrons are likely to be found.
Orbitals are located at discrete distances from the nucleus.
Electrons closer to the nucleus have lower energy.
True or False:
The periodic table organizes elements based on atomic mass.
False
Elements are arranged by atomic number, not mass, in the periodic table, showing trends in their properties.
Describe the Bohr model of the atom.
It shows an atom as a central nucleus containing protons and neutrons with the electrons in circular orbits around the nucleus at fixed energy levels.
It explains atomic spectra but is limited for complex atoms.
Fill in the blank:
The ground state energy for the hydrogen atom is _______.
-13.6 eV
The ground state energy is the lowest energy level of an electron in a hydrogen atom. This value, -13.6 eV, represents the energy required to remove the electron from the atom (ionization energy) when it is in its most stable state.
What describes the arrangement of electrons in an atom’s electron shells?
Electron configuration
Electron configuration indicates how electrons are distributed in an atom’s orbitals, influencing its chemical behavior and bonding. Examples include configurations like 1s² 2s² 2p⁶.
What is the electron configuration for hydrogen?
1s¹
Hydrogen has one electron, which occupies the 1s orbital.
What type of radiation is emitted when an electron transitions from a higher energy state to a lower energy state?
Electromagnetic radiation (light).
This release of energy is typically observed as visible light or photons, depending on the energy difference.
True or False:
Valence electrons are the outermost electrons that determine an atom’s reactivity.
True
These electrons are key in determining an atom’s chemical reactivity and bonding behavior.
True or False:
Hund’s Rule states that electrons in subshells must pair up in orbitals before occupying separate orbitals.
False
Hund’s Rule states that electrons occupy separate orbitals in a subshell before pairing up to minimize electron-electron repulsion.
What is an electron shell?
An electron shell is the space around the nucleus in which an electron can be found.
Electron shells represent areas where electrons are most likely to be located and are numbered based on their distance from the nucleus.
What is the order of filling electron shells?
1s, 2s, 2p, 3s, 3p, 4s, 4d, 4p, …
This order follows the Aufbau principle, where electrons fill orbitals from lowest to highest energy.
What is the Aufbau Principle?
Electrons fill lower energy levels before higher ones.
This principle explains why 1s is filled before 2s, and 2s before 2p.
What are the possible subshells an electron can occupy?
s, p, d, f
Each subshell has a specific number of orbitals: s (1 orbital), p (3 orbitals), d (5 orbitals), and f (7 orbitals).
True or False:
When an electron moves from n = 2 to n = 3, it releases energy.
False
When an electron transitions to a higher energy level (n = 3), it absorbs energy, not releases it.
What happens when an electron absorbs energy?
It moves to a higher energy level.
Absorbing energy causes the electron to jump from its ground state to an excited state, where it may later release energy.
What are the four quantum numbers used to describe an electron?
- n
- l
- ml
- ms
Each quantum number describes a specific property of an electron’s state: principal quantum number (n), angular quantum number (l), magnetic quantum number (ml), and spin quantum number (ms).
What is the maximum number of electrons that can occupy an s sublevel?
2
The s sublevel consists of one orbital, which can hold two electrons with opposite spins.
What are the possible spin states of an electron?
+1/2 or -1/2
Electrons must have opposite spins when occupying the same orbital, as dictated by the Pauli Exclusion Principle.
What does the quantum number “n” represent in an electron’s state?
The principal energy level.
The principal quantum number (n) indicates the distance of an electron from the nucleus and its energy level, with higher values of n corresponding to higher energy levels.
What is shorthand electron configuration?
Using the previous row’s noble gas as a starting point.
This method simplifies electron configuration by referencing the nearest noble gas to reduce repetition.
What is an absorption spectrum?
A spectrum showing absorbed wavelengths of light.
It appears as dark lines where light is absorbed by atoms or molecules.
What is an emission spectrum?
A spectrum showing light emitted by atoms or molecules.
It appears as bright lines at specific wavelengths.
What determines the color of light emitted by an atom?
The energy difference between two electronic levels.
Larger energy gaps produce shorter wavelengths.
The specific wavelengths correspond to different colors in the visible spectrum.
Explain why visible spectra are limited to certain colors.
Only specific wavelengths correspond to energy differences in visible transitions.
Visible transitions occur in the range of 400 to 700 nm.
True or False:
Absorption spectra identify unknown substances.
True
Comparing absorption patterns reveals unknown compounds.
Define:
radioactive decay
A spontaneous process where unstable nuclei emit radiation to become stable.
This process continues until a stable nucleus is formed.
It can involve a change in the number of protons and/or neutrons.
When is a nucleus considered unstable?
When nuclear forces cannot overcome electrostatic repulsive forces between protons.
An unstable nucleus undergoes a change that releases energy in the form of a particle or ionizing radiation.
Stability depends on the ratio of neutrons to protons (n/p).
List the three major types of radioactive decay.
- Alpha decay
- Beta decay
- Gamma decay
Neutron radiation is also another type.
What are beta particles?
High-speed electrons or positrons released in a beta decay.
These particles are produced when a proton is broken into a smaller particle. They have moderate penetration power, but can be stopped by aluminum.
When does an alpha decay occur?
When a nucleus with too many protons emits an alpha particle (α).
Define:
alpha particles
They consist of two protons and two neutrons released during alpha decay.
Alpha particles are equivalent to helium nuclei. They tend to be heavy and positively charged, but have low penetration power. They can be stopped by something as thin as a sheet of paper!
Define:
gamma decay
It is the release of high-energy photons from an unstable nucleus without changing its composition.
Gamma rays are electromagnetic waves with high energy but no mass. They can be dangerous to humans and can be stopped by thick lead.
Define:
beta decay
A type of radioactive decay where a radioisotope emits a beta particle (β), equivalent to an electron.
It increases or decresases the atomic number of a radioisotope by one, but does not change the mass.
Compare the penetration power of alpha, beta, and gamma radiation.
- Alpha: low, stopped by paper
- Beta: moderate, stopped by aluminum
- Gamma: high, stopped by thick lead
The penetration depends on the type of radiation and can determine the level of danger of that kind of radiation to humans.
Gamma rays can penetrate and ionize tissues, create free radicals, and cause cancers.
What is nuclear notation?
A way to denote changes in the nuclear structure using the elemental symbol, atomic number, and atomic mass.
Example: Uranium can be written as 238/92 U.
Define:
half-life
The amount of time it takes for half of the nucleus of an element to break down.
It is a measure of the rate at which radioactive decay occurs.
It can range from seconds to years.
How do you calculate the number of half-lives that have passed?
n = t / T
Where t is the time that has passed and T is the length of the half-life.
What type of graph represents radioactive decay?
An exponential decay graph.
The graph is exponential because the decay function involves raising a fraction (1/2) to the power of the number of half-lives elapsed.
The y-value decreases and approaches zero as the x-value increases.
How can you determine half-lives from a decay graph?
By finding the x-value corresponding to the y-value that is half of the initial amount.
For example, if the initial y-value is 15 g, half-life corresponds to 7.5 g on the y-axis.
True or False:
All elements undergo radioactive decay at the same rate.
False
Decay rates vary depending on the isotope’s half-life.
Define:
nuclear fission
A large nucleus splits into two or more smaller nuclei.
To create this kind of reaction, unstable heavy atoms are hit with neutrons. The additional neutrons lead to more instability, which then leads to the split of the nucleus into smaller atoms or neutrons.
Define:
nuclear fusion
Two light nuclei combine to form a heavier nuclei.
When this happens, the final resultant atom is lighter than the two individual pieces. Since mass was lost in the reaction, a large amount of energy is released.
What is a nuclear reaction?
A process involving the transformation of atomic nuclei.
What is the difference between nuclear fusion from nuclear fission?
- Fusion: two light nuclei combine to form a heavier nucleus.
- Fission: large nucleus splits into two or more smaller nuclei.
One reaction represents the combination of nuclei, while the other represents the split of a large nuclei. Both produce energy, but we are only able to easily harness the energy created from fission.
Fill in the blanks:
In nuclear fission, a heavy nucleus splits into ________ and _______.
smaller nuclei; neutrons
Energy is also released in the process.
This process is the basis for nuclear power generation.
Define:
nuclear equations
Symbolic representations of nuclear reactions written with reactants and products separated by an arrow.
Example format: Reactants ⟶ Products.
Define:
nuclear chemistry
A field of chemistry that deals with the use of radioactive isotopes and other nuclear reactions.
It is used in daily our lives for:
- Diagnosing diseases
- Treating medical conditions
- Determining the age of artifacts
- Energy production
What is a radioactive tracer?
A radioactive isotope used to track chemical pathways or locate abnormalities in the body.
Stable atoms in the body are replaced by radioactive atoms, which help in diagnosing diseases.
Define:
carbon dating
A method that uses the decay of carbon-14 to determine the age of artifacts.
It relies on measuring the ratio of carbon-14 to carbon-12 in once-living materials.
The half-life of carbon-14 is approximately 5,730 years.
Every 5,730 years, half of the carbon-14 in an artifact decays into nitrogen through a beta decay.
How is gamma decay used in the medical field?
- Radiation therapy for cancer
- Sterilizing equipment
- Diagnostic imaging tracers
Gamma rays can pass through human tissue, which allows for diagnostics and therapeutic uses. However, they must be used carefully because they have the potential to damage human tissue and DNA.
