Chemistry Chapter 3 Vocabulary

This is for Holt Chemistry users in 11th grade

Law of definite proportions

The law that states that a chemical compound always contains the same elements in exactly the same proportions by weight or mass.

Law of conservation of mass

The law that states that mass cannot be created or destroyed in ordinary chemical and physical changes.

Law of multiple proportions

The law that states when two elements combine to form two or more compounds, the mass of one element that combines with a given mass of the other is in the ratio of small whole numbers.

Electron

A subatomic particle that has a negative electric charge.

Nucleus

An atom’s central region, which is made up of protons and neutrons.

Proton

A subatomic particle that has a positive charge and that is found in the nucleus of an atom.

Neutron

A subatomic particle that has no charge and that is found in the nucleus of an atom.

Atomic number

The number of protons in the nucleus of an atom.

Mass number

The sum of the numbers of protons and neutrons of the nucleus of an atom.

Isotope

An atom that has the same number of protons as other atoms of the same element but has a different number of neutrons.

Orbital

A region in an atom where there is a high probability of finding electrons. 

Electromagnetic spectrum

All of the frequencies or wavelengths of electromagnetic radiation.

Ground state

The lowest energy state of a quantized system.

Excited state

A state in which an atom has more energy than it does at its ground state.

Quantum number

A number that specifies the properties of electrons.

Pauli exclusion principle

The principle that states that two particles of a certain class cannot be in the exact same energy state.

Electron configuration

The arrangement of electrons in an atom.

Aufbau principle

The principle that states that the structure of each successive element is obtained by adding one proton to the nucleus of the atom and one electron in the lowest energy orbital that is available.

Hund’s rule

The rule that states that for an atom in the ground state, the number of unpaired electrons is the maximum possible and these unpaired electrons have the same spin.

Atomic mass

The mass of an atom expressed in atomic mass units.

Mole

The SI base unit used to measure the amount of a substance whose number of particles is the same as the number of atoms in 12 g of carbon-12.

Molar mass

The mass in grams of 1 mol of a substance.

Avogadro’s number

6.022×10²3, the number of atoms or molecules in 1 mol.