Unit 1: Atomic Structure and Properties

Avagadro's Number

Avagadro's Number

Provides a connection between the number of moles in a pure sample of a substance and the number of particles or formula units of that substance

Mass Spectroscopy

Can be used to to determine the identity of isotopes of the element, relative abundance of each isotope in nature, and/or average atomic mass.

Empirical Formula

Chemical formula that lists the lowest whole number ratio of atoms tof the elements in a compound

Molecular Formula

A chemical formula that shows the number and kinds of atoms in a molecule, but not the arrangement of the atoms.

Law of Definite Proportions

The ratio of the masses of the elements in any pure sample is always the same.

Pure Substance

A sample of matter, either a single element or a single compound, that has definite chemical and physical properties

Mixture

A combination of two or more substances that are not chemically combined

Homogeneous

Of the same kind

Heterogeneous

different; dissimilar

Aufbau Principle

An electron occupies the lowest-energy orbital that can receive it

Pauli Exclusion Principle

An atomic orbital may describe at most two electrons, each with opposite spin direction

Hund's Rule

Electrons occupy orbitals of the same energy in a way that makes the number of electrons with the same spin direction as large as possible

Degenerate Orbitals

Orbitals that have the same energy

Coulomb's Law

Force between charged objects depends on the distance between the objects and the magnitude of the charges.

Energy Levels

Also known as shells, the possible energies that electrons in an atom can have (n=1 to n=7)

Subshell

s, p, d, f

Orbital

most probable region where an electron is located. Located within subshells

Core Electrons

The electrons in the inner shells of an atom; these electrons are not involved in forming bonds.

Valence Electrons

Electrons on the outermost energy level of an atom; bonding electrons

Cation

A positively charged ion; usually a metal

Anion

A negatively charged ion; usually a non-metal

Photoelectron Spectroscopy (PES)

Measures the energies of the electrons in a given shell. The position of the peak is related to the energy required to remove an electron from the subshell, and the height is proportional to the number of electrons in the subshell.

Effective Nuclear Charge

Also known as Zeff The actual nuclear charge experienced by an electron, defined as the charge of the nucleus plus the charge of the shielding electrons

Shielding

The effect on an electron of repulsion by electrons in lower-energy orbitals that screen it from the full effects of nuclear charge

Ionization Energy

The amount of energy required to remove an electron from an atom

Atomic Radii

Half the distance between the nuclei of identical atoms that are bonded together

Ionic Radii

measured distance from the center of an ion to its outer electrons

Electron Affinity

The energy change associated with the addition of an electron to a gaseous atom

Electronegativity

A measure of the ability of an atom in a chemical compound to attract electrons