CHEM131: Introduction to Atoms and Atomic Theory

These flashcards cover key vocabulary and concepts from the introduction to atomic theory and structure as outlined in CHEM131 lecture notes.

Atomic Theory

A scientific theory that states that matter is composed of discrete units called atoms.

Law of Conservation of Matter

Matter can neither be created nor destroyed; it can only change forms.

Law of Multiple Proportions

When two elements combine to form more than one compound, the ratios of the masses of the elements can be expressed as small whole numbers.

Cation

A positively charged ion, formed when an atom loses electrons.

Anion

A negatively charged ion, formed when an atom gains electrons.

Isotopes

Atoms of the same element that differ in their number of neutrons, thus having different mass numbers.

Mass Spectrometry

A technique used to measure the mass-to-charge ratio of ions to identify and quantify molecules.

Avogadro’s Number

6.022 x 10^23. Atoms per mole

Molar Mass

The mass of one mole of a substance, typically expressed in grams per mole (g/mol).

Plum Pudding Model

J.J. Thomson's model of the atom, which suggested that atoms are composed of a positive 'pudding' with negative electrons dispersed throughout.

Nuclear Model

Rutherford's model of the atom, where atoms consist of a small, dense nucleus surrounded by electrons.

Cathode Rays

Streams of electrons observed in vacuum tubes, which can be deflected by electric and magnetic fields.

Electron

A negatively charged subatomic particle found outside the nucleus of an atom.

Proton

A positively charged subatomic particle found in the nucleus of an atom.

Neutron

A neutral subatomic particle found in the nucleus of an atom.

Atomic Number (Z)

The number of protons in the nucleus of an atom, which determines the element's identity.

Mass Number (A)

The total number of protons and neutrons in an atom's nucleus.

Atomic Mass Unit (amu)

A unit of mass used to express atomic and molecular weights, approximately equal to the mass of one proton or neutron.

Average Atomic Mass

The weighted average of the masses of all naturally occurring isotopes of an element, based on their relative abundances.

Dalton's Atomic Theory Postulates

1. All matter is composed of indivisible atoms.
2. Atoms of a given element are identical in mass and properties.
3. Compounds are formed by a combination of two or more different kinds of atoms.
4. A chemical reaction is a rearrangement of atoms.

Quantum Mechanical Model of the Atom

The current model of the atom that describes electrons in terms of probabilities, residing in orbitals rather than fixed orbits.

Orbital

A region around the nucleus where an electron is most likely to be found, characterized by a specific shape and energy level.

Heisenberg Uncertainty Principle

States that it is impossible to simultaneously know precisely both the position and momentum of a particle, such as an electron.

Pauli Exclusion Principle

States that no two electrons in the same atom can have the same set of four quantum numbers. Each orbital can hold a maximum of two electrons with opposite spins.