Chem Chapter 9

Hydrogen

A highly reactive gas that exists as diatomic molecules (H2) and can easily bond with other elements.

Helium

An inert gas with a stable electron configuration consisting of two electrons.

Atomic Number

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

Wavelength

The distance between consecutive wave crests, typically measured in nanometers (nm) for light.

Frequency

The number of cycles of a wave that pass a given point per second, inversely related to wavelength.

Photon

A particle of light that carries a quantum of energy, dependent on the light's wavelength.

Bohr Model

A model of the atom suggesting that electrons orbit the nucleus at fixed distances with quantized energies.

Quantum-Mechanical Model

An advanced model of the atom that describes electrons as existing in probability distributions rather than fixed orbits.

Ionization Energy

The energy required to remove an electron from an atom in the gas phase.

Valence Electrons

Electrons in the outermost shell of an atom that are responsible for chemical bonding.

Core Electrons

Electrons that are not in the outermost shell and do not participate in chemical bonding.

Periodic Law

The law stating that the properties of elements are periodic functions of their atomic numbers.

Noble Gases

Inert gases found in Group 18 of the periodic table that have a complete valence shell.

Alkali Metals

Elements in Group 1 that are highly reactive, with one valence electron that they easily lose to form cations.

Alkaline Earth Metals

Elements in Group 2 that typically lose two valence electrons to form 2+ cations.

Halogens

Elements in Group 17 that are highly reactive nonmetals with seven valence electrons.

Electromagnetic Radiation

Energy that travels through space as a combination of electric and magnetic fields.

Emission Spectrum

The spectrum of light emitted by atoms when electrons transition between energy levels.

Quantum Number

A number that specifies the energy level of an electron in an atom.