Quantum Theory and the Electronic Structure of Atoms

Flashcards covering the Quantum Theory of atoms, electronic configurations, periodic trends, subatomic particles, and basic laws of matter.

Mendeleev's Periodic Table

An early chart where elements were arranged by increasing atomic mass, allowing for the prediction of new elements based on repeating property patterns.

Modern Periodic Table

The current arrangement of all known chemical elements organized by increasing atomic number rather than atomic mass.

Atomic Mass

The total mass of the protons and neutrons in the nucleus, measured in Atomic Mass Units ($\text{amu}$).

Atomic Radius

The measure of the physical size of an atom, defined as the distance from the center of the nucleus to the outer boundary of the electron cloud; usually measured in Picometers ($\text{pm}$) or Angstroms ($\text{\AA}$).

Periodic Trend: Across a Period

As one moves from left to right, atomic mass increases and atomic radius decreases because more protons pull electrons closer to the nucleus.

Periodic Trend: Down a Group

As one moves from top to bottom, both atomic mass and atomic radius increase because more electron shells are added.

Aufbau Principle

A rule stating that in the ground state of an atom or ion, electrons fill the subshells of the lowest available energy first before moving to higher energy levels.

Pauli Exclusion Principle

A principle stating that no two electrons in an atom can have the same set of four quantum numbers, and each orbital can hold a maximum of two electrons with opposite spins.

Hund’s Rule

The rule that electrons fill a subshell singly before forming any pairs, and each electron in a single occupied orbital has the same spin.

Principal Quantum Number ($n$)

Indicates the main energy level or shell where an electron is found, with values $n = 1, 2, 3, 4, \dots$; higher values mean higher energy and greater distance from the nucleus.

Azimuthal Quantum Number ($l$)

Defines the shape of the orbital or subshell, where $l = 0$ is s (spherical), $l = 1$ is p (dumbbell), $l = 2$ is d, and $l = 3$ is f.

Magnetic Quantum Number ($m_l$)

Describes the orientation of the orbital in space, with values ranging from $-l$ to $+l$. For example, a p orbital ($l = 1$) has three orientations ($m_l = -1, 0, +1$).

Spin Quantum Number ($m_s$)

Indicates the direction of electron spin within an orbital, with possible values of $+1/2$ (spin up) or $-1/2$ (spin down).

Maximum Electron Capacity

The formula used to determine the maximum number of electrons each main energy level can hold, calculated as $2n^2$. For example, level $n=3$ can hold $18$ electrons.

Law of Conservation of Mass

States that matter can neither be created nor destroyed, meaning the mass of the products in a chemical reaction must equal the mass of the reactants.

Law of Constant Composition

Also known as the Law of Definite Composition, it states that all samples of a given chemical compound contain the same elements in the same proportion by mass.

Law of Multiple Proportions

States that when two elements form more than one compound, the masses of one element that combine with a fixed mass of the other are in a ratio of small whole numbers.

Dalton’s Atomic Theory

Proposed by John Dalton, it establishes that atoms are indivisible particles with fixed weights and that compounds are formed by the combination of atoms in specific relative numbers.

Protons

Positively-charged particles located inside the nucleus with a mass of approximately $1.0073\, \text{amu}$, discovered by Ernest Rutherford and Eugene Goldstein.

Neutrons

Neutral particles located inside the nucleus with a mass of approximately $1.007\, \text{amu}$, discovered by James Chadwick in 1932.

Electrons

Negatively-charged particles that spin around the nucleus in orbits or shells, with a very small mass of approximately $1/1836\, \text{amu}$ or $0.00055\, \text{amu}$.

Atomic Number ($Z$)

The number of protons inside an atom's nucleus, which also equals the number of electrons in a neutral atom.

Mass number ($A$)

The sum of the number of protons and the number of neutrons in the nucleus ($A = Z + N$).

Isotopes

Atoms of the same element that have the same number of protons but a different number of neutrons.

Protium

The most common and abundant isotope of hydrogen, possessing one proton and no neutrons, with a mass number of $1$.

Deuterium

An isotope of hydrogen often called heavy hydrogen, containing one proton and one neutron, with a mass number of $2$.

Tritium

An isotope of hydrogen with one proton and two neutrons ($A=3$), often found as a waste product in nuclear reactions.

Diatomic Molecules

Molecules containing only two atoms, classified as homonuclear (same element, like $Cl_2$) or heteronuclear (different elements, like $HCl$).

Ions

Atoms or molecules that possess a net charge because the number of protons does not equal the number of electrons.

Cation

A positively-charged ion resulting from the loss of electrons.

Anion

A negatively-charged ion resulting from the gain of electrons.