Definition: Electrons are negatively charged particles that orbit the nucleus in specific energy levels called shells.

Highlight: Each electron shell has a specific capacity: Shell 1 holds 2 electrons, Shell 2 holds 8 electrons, and Shell 3 holds 18 electrons.

Example: The periodic table provides key information including the element's symbol, atomic number (number of protons), and atomic mass (protons + neutrons).

Vocabulary: Compounds are formed when two or more elements join together, while molecules are specifically formed when two of the same elements combine (like O₂).

Definition: Matter is anything that occupies space or has mass, following the conservation principle that it can neither be created nor destroyed.

Vocabulary: Atoms are the simplest particles of elements that retain all properties of that element.

Highlight: The nucleus contains most of the atom's mass and consists of protons and neutrons.

Example: Isotopes demonstrate how atoms of the same element can have different masses, such as Carbon-12 and Carbon-13, which have the same number of protons but different numbers of neutrons.