Electron Shells and Isotopes (Page 1 Notes)

Vocabulary flashcards covering key terms from Page 1 notes on isotopes, charge, nucleus, and electron shells.

Isotope

Variants of the same element that have the same number of protons but different numbers of neutrons; mass number differs.

Proton

Positively charged subatomic particle located in the nucleus; defines the element's identity (atomic number).

Neutron

Electrically neutral subatomic particle in the nucleus; contributes to atomic mass and isotope variation.

Electron

Negatively charged subatomic particle that orbits the nucleus in electron shells; number equals protons in a neutral atom.

Nucleus

Center of the atom containing protons and neutrons; carries the positive charge of the atom.

First electron shell

Innermost energy level closest to the nucleus; maximum capacity 2 electrons; lowest energy.

Second electron shell

Outer of the first shell; holds up to 8 electrons; higher energy than the first shell.

Third electron shell

Outer shell in many atoms; can hold up to 18 electrons when it is the valence shell; higher energy than inner shells.

Valence shell

Outermost electron shell; determines chemical properties and bonding; capacity up to 18 electrons.

Neutral atom

An atom with equal numbers of protons and electrons; net charge is zero.

Shell capacity (per shell)

First shell: 2 electrons; Second shell: 8 electrons; Third shell: up to 18 electrons (when outermost).

Energy order of shells

Electrons fill inner shells first because they have lower energy than outer shells.