Quantum Mechanics and Periodic Table Basics

The noble gases are a group of chemical elements with similar properties. They are all odorless, colorless gases under standard conditions. They are all very unreactive, because their outer shell of electrons is full. They are known as the inert gases.

The alkali metals are a group of chemical elements with similar properties. They are all soft, silvery-white, highly reactive metals. They have low melting points and low densities. They readily form ions with a +1 charge.

The halogens are a group of chemical elements with similar properties. They are all nonmetals and exist as diatomic molecules at room temperature. They are very reactive, and tend to gain one electron to form ions with a -1 charge.

The alkaline earth metals are a group of chemical elements with similar properties. They are all silvery-white, reactive metals. They have relatively high melting points and densities, compared to the alkali metals. They readily form ions with a +2 charge.

The principle quantum number (n) describes the electron shell. This determines the energy level and distance from the nucleus. As the value of n increases, Energy increases and the distance from the nucleus also increases. The higher the value of n, the bigger the atom.

The angular momentum quantum number (l) describes the subshells which define the shape of the orbital. l ranges from 0 to n-1. l=0 is s, l=1 is p, l=2 is d, l=3 is f.

The magnetic quantum number (ml) describes the orientation of the electron orbital in space. It takes on the values of (-l) to (+l) including 0. For s subshells, l=0, so ml=0 means there is only one orientation. For p subshells, l=1, so ml = -1, 0, +1 means there are three orientations.

The spin quantum number (ms) describes the intrinsic angular momentum of an electron. It's called 'spin' because it originates from the electron spinning. Its value can be either +1/2 or -1/2. It dictates the orientation of the spin angular momentum of an electron in an orbital..

The Pauli exclusion principle states that no two electrons in an atom can have the same set of four quantum numbers. This means that each orbital can hold a maximum of two electrons, and they must have opposite spins.

Hund's rule states that electrons will individually occupy each orbital within a subshell before doubling up in any one orbital. This minimizes electron repulsion and maximizes stability

The Aufbau principle states that electrons are added to orbitals in order of increasing energy. This means that we fill orbitals in a specific order based on their energy levels. The order of increasing energy of orbitals is typically 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p

The effective nuclear charge (Zeff) is the net positive charge experienced by an electron in a multi-electron atom: Zeff = Z - S where Z is the atomic number and S is the number of shielding electrons or core electrons. Zeff is a measure of the attraction between the nucleus and an electron. The greater Zeff the stronger the attraction between the nucleus and the electron.

The shielding effect describes the reduction in attraction between the nucleus and an electron caused by the presence of other electrons in the atom. Electrons in inner shells (core electrons) 'shield' the outer electrons from experiencing the full nuclear charge. This effect is important in understanding periodic trends.

Ionization energy is the energy required to remove an electron from a gaseous atom in its ground state. The first ionization energy is the energy required to remove the first electron. As you go from left to right across a period, the ionization energy increases due to increasing effective nuclear charge, making it harder to remove an electron. As you go down a group, ionization energy decreases because the electrons are farther from the nucleus and shielded better by the core electrons.

Electron affinity is the change in energy that occurs when an electron is added to a gaseous atom in its ground state. A negative electron affinity means the formation of a negative ion is exothermic (releases energy). Electron affinity is the opposite of ionization energy. As you go from left to right across a period, electron affinity generally increases, due to increasing effective nuclear charge.

Electronegativity is a measure of an atom's ability to attract electrons in a chemical bond. The higher the electronegativity, the stronger the pull on the electrons. Electronegativity generally increases from left to right across a period and decreases from top to bottom within a group.

Atomic radius is a measure of the size of an atom. It is typically defined as half the distance between the nuclei of two identical atoms bonded together. Atomic radius generally decreases from left to right across a period, due to increasing effective nuclear charge. Atomic radius generally increases going down a group, due to increasing number of electron shells and shielding.

Ionic radius measures the size of an ion. Cations are smaller than their parent atoms because they have lost electrons, reducing electron repulsion. Anions are bigger than their parent atoms, because they have gained electrons, increasing electron-electron repulsion.

Paramagnetism occurs when an atom or molecule has unpaired electrons. Such species are attracted to a magnetic field.

Diamagnetism occurs when an atom or molecule has all of its electrons paired. Such species are weakly repelled by a magnetic field.

The valence electrons are the electrons in the outermost shell of an atom. Valence electrons are the outermost electrons of an atom. They are the electrons that are involved in chemical bonding and determine the element's reactivity.

The ground state electronic configuration of an atom is the arrangement of electrons in the orbitals of an atom, with the lowest possible total energy. The electrons occupy the orbitals according to the Aufbau principle, Pauli's exclusion principle, and Hund's rule.

A quantum number is a set of numbers that describes the properties of an atomic electron, such as energy, orbital shape, and spatial orientation. Quantum numbers arise from the solution of the Schrodinger equation and represent quantized properties of atomic electrons.

A wave function, also known as an orbital, is defined as a mathematical description of the behavior of an electron in an atom. The square of the wave function gives the probability of finding an electron at a particular point in space.

The Schrodinger equation explains the behavior of electrons in atoms, and how they interact with the nucleus. It's a fundamental equation in quantum mechanics.

Quantum mechanics is a theory that describes the behavior of matter at the atomic and subatomic levels. It differs from classical mechanics, which describes the behavior of everyday objects. Quantum mechanics is based on the idea that energy, momentum, angular momentum, and other quantities are quantized, meaning they can only exist in discrete values.

The periodic table is a tabular arrangement of chemical elements, ordered by atomic number, electron configuration, and recurring chemical properties. The table is divided into periods (rows) and groups (columns).