Chapter 3: Atoms & Moles Vocabulary

A set of vocabulary flashcards defining fundamental chemical concepts, subatomic particles, quantum mechanics rules, and atomic laws from Chapter 3: Atoms & Moles.

Law of Multiple Proportions

When elements combine to form different compounds, the masses of one element that combine with a fixed mass of another are in a small whole-number ratio.

Proton

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

Atomic Number

The number of protons in the nucleus of an atom. This number is the same for all atoms of an element.

Isotope

An atom with the same atomic number as other atoms of an element but a different atomic mass number.

Ground State

The lowest energy state of a quantized system.

Quantum Number

A number that specifies the properties of electrons.

Aufbau Principle

Electrons fill the lowest available energy orbitals before occupying higher-energy orbitals.

Mole

The amount of a substance containing $6.022 \times 10^{23}$ particles.

Electron

A subatomic particle with a negative charge.

Neutron

A subatomic particle with no charge that is found in the nucleus.

Law of Definite Proportions

A chemical compound always contains the same elements in exactly the same proportions by mass.

Mass Number

The sum of the number of protons and neutrons in the nucleus.

Orbital

A region in an atom with a high probability of finding electrons.

Excited State

A state in which an atom has more energy than its normal (ground) state.

Pauli Exclusion Principle

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

Molar Mass

The mass in grams of one mole of a substance.

Hund's Rule

For orbitals of equal energy, electrons occupy each orbital singly before any orbital receives a second electron.