Comprehensive Study Notes on Matter, Atomic Structure, Isotopes, and Chemical Compounds

Matter

Any substance that possesses mass and occupies physical space, existing in solid, liquid, or gas states within the human body.

CHAN

An acronym for the four major elements making up $96\%$ of human body mass by weight: Carbon, Hydrogen, Oxygen, and Nitrogen.

Proton

A positively charged ($+$) subatomic particle located in the central nucleus of an atom with a mass equal to a neutron.

Neutron

A neutral ($0$ charge) subatomic particle located in the central nucleus of an atom.

Electron

An extremely light, negatively charged ($-$) subatomic particle that orbits the central nucleus within electron shells.

Atomic Number

The number on the periodic table that indicates the exact count of protons in an atom's nucleus, which also equals the number of electrons in a neutral atom.

Isotope

A structural variation of a chemical element that has the same number of protons and electrons, but a different number of neutrons.

Radioisotope

An unstable isotope that spontaneously breaks down into a stable form, emitting radiation such as alpha particles, beta particles, or gamma rays.

Half-Life

The amount of time required for exactly $50\%$ of a given quantity of a radioisotope to decay into a stable form.

Molecular Formula

A notation defining the exact identity and quantity of each atom in a compound using element symbols and subscripts (e.g., $CO_2$, $H_2O$).

Structural Formula

A structural representation showing the spatial arrangement and physical positioning of atoms and bonds within a compound.