h, Understanding Electron Configuration and Valence Electrons, Atomic Models and Electron Behavior in Atoms, Modern Atomic Theory and the Electromagnetic Spectrum

What is radioactivity?

Radioactivity is the process by which nuclei of unstable isotopes emit radiation.

What is a radioisotope?

A radioisotope is an unstable isotope that is subject to radioactive decay.

What is radioactive decay?

Radioactive decay is the spontaneous breaking down of an unstable atomic nucleus to produce radiation and a more stable nucleus of a different element.

Does radioactive decay require an input of energy?

No, radioactive decay does not require an input of energy.

What factors do not affect radioactive decay?

Radioactive decay is not affected by pressure, temperature, catalysts, or the compound the isotope is in.

What does the discovery of radioactivity disprove?

The discovery of radioactivity disproved Dalton's theory that atoms are indivisible.

What is transmutation?

Transmutation is the changing of one element into another element by radioactive decay.

What determines the stability of a nucleus?

The stability of a nucleus depends on the ratio of neutrons to protons.

What is the neutron-to-proton ratio for stable nuclei of low atomic number?

For elements with atomic numbers below ~20, the neutron-to-proton ratio is around 1.

What is the neutron-to-proton ratio for stable nuclei of higher atomic number?

For elements above atomic number 20, stable nuclei have more neutrons than protons.

What is the band of stability?

The band of stability is a pattern formed by a neutron-vs-proton plot of all stable nuclei.

What is the atomic number (Z)?

The atomic number (Z) is the number of protons in a nucleus.

What is the mass number (A)?

The mass number (A) is the sum of the number of protons and neutrons.

What are isotopes?

Isotopes are atoms with identical atomic numbers but different mass numbers.

What is a nuclide?

A nuclide is each unique atom.

What is a radioactive nucleus?

A nucleus that spontaneously decomposes, forming a different nucleus and producing one or more particles.

What does a nuclear equation show?

The radioactive decomposition of an element.

What are the types of radiation?

Alpha, beta, and gamma radiation.

alpha decay

Alpha (α)

What is it?: Helium nucleus (+2 charge)

Mass # Change: -4

Atomic # Change: -2

When does it happen?: With heavier elements; if the nucleus has too many protons and neutrons

Example: See above

beta decay

Beta (β)

What is it?: Electron ejected from nucleus (-1 charge)

Mass # Change: Stays same

Atomic # Change: +1

When does it happen?: If the nucleus has too many neutrons; neutron (n0) decays into a proton (p+) and an electron (e-), which is ejected from the nucleus

gamma decay

Gamma (γ)

What is it?: A high-energy photon (electromagnetic radiation, so no charge or mass)

Mass # Change: Stays same

Atomic # Change: Stays same

When does it happen?: Allows the nucleus to get rid of excess energy to stabilize; often accompanies other radiation

Example: See above

Positron Emission

Positron Emission (β⁺)

What is it?: Particle with mass of an electron but a + charge

Mass # Change: Stays same

Atomic # Change: -1

When does it happen?: If the nucleus has too many protons, it emits a positron to decrease protons and increase neutrons; proton (p+) converts to a neutron (n0) and emits a positron (β⁺)

What holds all atomic nuclei together?

The strong nuclear force

What type of force acts between nuclear particles that are extremely close together?

An attractive force

What does the strong nuclear force overcome at small distances?

Electrostatic repulsion

What are elements with atomic numbers above 92 called?

Transuranium elements

How can transmutation occur?

By decay or bombardment

What were the first artificial elements produced in the 1940s?

Neptunium (Np) and Plutonium (Pu)

How many artificial elements have been produced since the 1940s?

26 artificial elements

What is nuclear transformation?

The change of one element into another

What is required for bombarding particles to penetrate a target in nuclear transformations?

They must move at a very high speed

How are high speeds for bombarding particles achieved?

Using various types of particle accelerators

What is a decay series?

A decay series is a series of radioisotopes produced by successive radioactive decay until a stable isotope is reached.

What is the heaviest radioisotope in a decay series called?

The heaviest radioisotope of each decay series is called the parent nuclide.

What are the radioisotopes produced by the decay of the parent nuclide called?

They are called the daughter nuclides.

What is the half-life?

The half-life is the time required for half of the original sample of radioactive nuclei to decay.

How are radioactive decay rates measured?

Radioactive decay rates are measured in half-lives.

What is the half-life of Thorium-219?

1.05 x 10^-6 seconds.

What is the half-life of Radon-222?

3.8 days.

What is the half-life of Carbon-14?

5730 years.

What is the half-life of Potassium-40?

1.28 x 10^9 years.

What is the half-life of Uranium-238?

4.47 x 10^9 years.

What is the formula to find the remaining amount of a radioactive element?

N = N0 (1/2)^n, where n is the number of half-lives that have passed, N0 is the initial amount, and N is the remaining amount.

How do you calculate the number of half-lives that have passed?

n = t/T, where t is the elapsed time and T is the duration of the half-life.

What are some medical uses of radioactive substances?

They are used for diagnosing, treating, and detecting diseases, including cancer.

How are radioactive substances used in food preservation?

They are used for sterilization of medical supplies and food preservation using gamma radiation.

What radioactive substance is commonly used in smoke detectors?

Americium-241

Which isotopes are used by geologists and archaeologists to date rocks and organic materials?

Potassium-40 and Carbon-14

What are radioactive tracers used for in medicine?

To observe organ functions and detect diseases.

How are radioactive tracers used in agriculture?

To measure fertilizer absorption.

What is the use of radioactive tracers in industry?

To locate leaks in underground pipes.

What is nuclear fission?

The process of splitting a heavy nucleus into smaller, more stable nuclei, releasing significant energy.

What is critical mass in nuclear fission?

The minimum amount of fissionable material needed to sustain a chain reaction.

What is nuclear fusion?

The process of joining smaller nuclei to form a larger nucleus, releasing more energy than fission.

Where does nuclear fusion naturally occur?

In stars like the sun.

What are the current applications of artificial nuclear fusion?

Limited applications, such as in hydrogen bombs.

Who wrote the first extensive list of all known elements in 1789?

Antoine Lavoisier

What did Jöns Jakob Berzelius develop in 1828?

A table of atomic weights and introduced letters to symbolize elements.

What did Johann Dobereiner attempt to do in 1829?

Group elements into triads with similar properties.

What was the state of element identification by 1860?

There were more than 60 identified elements, and chemists struggled to classify them and determine their atomic masses.

Who developed a workable method to accurately measure atomic masses in 1860?

Stanislao Cannizzaro

What did Alexandre-Émile Beguiler de Chancourtois do in 1862?

Arranged the elements in order of increasing atomic weights.

What is the 'Law of Octaves' proposed by John Newland in 1864?

A method to order elements where certain chemical properties repeat roughly every 8 elements.

What did Lothar Meyer compile in 1869?

A table of 56 elements based on periodic properties arranged by increasing atomic weight.

Electron configuration

The way that electrons are systematically arranged around the nucleus of an atom and accounted for.

Aufbau Principle

An electron will occupy the lowest energy configuration available to it.

Hund's Rule

Orbitals of equal energy are each occupied by one electron before any orbital can be occupied by a second electron.

Pauli Exclusion Principle

No two electrons in the same atom can have the same set of 4 quantum numbers.

Orbital notation

A method to represent electron configurations showing a line with the orbital's name written below.

Electron Configuration Notation

A method that eliminates lines and arrows, showing the number of electrons by adding a superscript to sublevel designation.

Noble-Gas Configuration

Simplifies the electron-configuration notation by including the noble gas of the previous period in brackets.

Valence Electrons

Electrons in the outermost orbitals in the highest principal energy level of an atom that determine chemical properties.

Core electrons

The inner shell electrons that are not involved in bonding atoms to each other.

Example of Electron Configuration for Phosphorus

1s22s22p63s23p3

Example of Electron Configuration for Iron

1s22s22p63s23p64s23d6

Example of Electron Configuration for Aluminum

1s22s22p63s23p1

Example of Noble-Gas Configuration for Phosphorus

[Ne] 3s23p3

Example of Noble-Gas Configuration for Iron

[Ar] 4s23d6

Example of Noble-Gas Configuration for Aluminum

[Ne] 3s23p1

Exceptions to Normal Order of Filling

Some half-filled orbital sublevels are not as chemically stable as alternate configurations.

Normal Configuration for Chromium

[Ar] 4s23d4

Exception Configuration for Chromium

[Ar] 4s13d5

Normal Configuration for Copper

[Ar] 4s23d9

Exception Configuration for Copper

[Ar] 4s13d10

Example of Valence Electrons for Sulfur

S [Ne] 3s2 3p4 has 6 valence electrons.

Example of Valence Electrons for Cesium

Cs [Xe] 6s1 has 1 valence electron.

Order of Orbital Filling

1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p.

Question about Electron Configuration

Which one is correct? The 3rd one!

Photoelectric Effect

Emission of electrons from materials upon light exposure.

Wave-Particle Duality

Concept that particles exhibit both wave and particle properties.

Rutherford's Model

Atom structure: empty space, dense nucleus, orbiting electrons.

Line Emission Spectra

Distinct light bands emitted by excited gas atoms.

Excited State

Higher energy state of an electron after energy absorption.

Ground State

Lowest energy state of an electron in an atom.

Niels Bohr

Proposed circular orbits for electrons with fixed energy.

Energy Level

Fixed energy state of an electron, akin to ladder rungs.

Photon

Light particle emitted when an electron returns to ground state.

Atomic Fingerprint

Unique bright-line emission spectrum of each element.

De Broglie Hypothesis

Electrons exhibit wave characteristics, traveling as waves.

Standing Wave

Wave pattern sustaining itself around the nucleus.