Atomic Structure, Mass, and Chemical Formulas

An atom's nucleus consists of protons (positively charged) and neutrons (uncharged), with electrons (negatively charged, very small mass) orbiting. The atomic number ($Z$) equals the number of protons (and electrons in a neutral atom), defining the element. Atomic mass ($A$) is the sum of protons and neutrons. Isotopes are atoms of the same element ($Z$) with different atomic masses ($A$) due to varying neutron counts. The Periodic Table displays $Z$, average atomic mass (a weighted average of isotopes), symbol, and name for each element.

Ions are charged particles derived from atoms by gaining (anions, negative) or losing (cations, positive) electrons. A molecule is a group of atoms held by chemical bonds, represented by a chemical formula. Molecular formulas show the exact number of atoms, while empirical formulas show the simplest whole-number ratio. Molecules can be visualized through various models like structural formulas and space-filling types. Isomers are non-identical compounds sharing the same molecular formula but differing in atom connectivity (constitutional) or 3D arrangement (stereoisomers).

Compounds are categorized as organic (carbon-based) or inorganic. Inorganic compounds can be molecular (discrete molecules) or ionic (composed of a lattice of cations and anions). Molecular Mass (MM) is the sum of atomic masses in a molecule, while Formula Mass (FM) is the sum of atomic masses in one formula unit of an ionic compound; both are calculated similarly in amu or Dalton. A mole (mol) is a quantity containing Avogadro's Number ($6.022 \times 10^{23}$) of particles. Molar Mass is the mass of $1$ mole of a substance, numerically equal to its MM or FM but expressed in g/mol, and is calculated by summing the atomic masses of all elements in its chemical formula.