$10^{-6}$ nano n $10^{-9}$ pico p $10^{-12}$

Mass vs. Weight:

Volume: Space occupied by matter. SI unit $m^3$. Common units: $L$ (liter), $cm^3$, $dm^3$. ($1 L = 1 dm^3 = 1000 cm^3$).

Density: Mass per unit volume. $D = \frac{M}{V}$. SI unit $kg \ m^{-3}$.

Temperature: Degree of hotness or coldness.

Significant Figures: Meaningful digits in a measured or calculated quantity.

Non-zero digits are significant.
Zeros between non-zero digits are significant.
Zeros to the left of the first non-zero digit are not significant.
Zeros at the end or right of a number are significant if they are on the right side of the decimal point.
Exact numbers (e.g., counting objects) have infinite significant figures.

Scientific Notation: $N \times 10^n$, where $N$ is a number between 1 and 10.

Law of Conservation of Mass (Lavoisier): Mass can neither be created nor destroyed in a chemical reaction. Total mass of reactants = Total mass of products.
Law of Definite Proportions (Proust): A given chemical compound always contains the same elements in the same proportion by mass, regardless of source. (e.g., $H_2O$ always has H:O ratio of 1:8 by mass).
Law of Multiple Proportions (Dalton): If two elements can combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element are in a ratio of small whole numbers. (e.g., $CO$ and $CO_2$).
Gay Lussac's Law of Gaseous Volumes: When gases combine or are produced in a chemical reaction, they do so in a simple ratio by volume, provided all gases are at the same temperature and pressure.
Avogadro's Law: Equal volumes of all gases at the same temperature and pressure contain equal number of molecules.

Matter consists of indivisible atoms.
All atoms of a given element have identical properties, including identical mass. Atoms of different elements differ in mass.
Compounds are formed when atoms of different elements combine in a fixed ratio.
Chemical reactions involve reorganization of atoms. Atoms are neither created nor destroyed.
Limitations: Failed to explain subatomic particles, isotopes, isobars.

Atomic Mass Unit (amu or u): Defined as exactly one-twelfth the mass of one atom of carbon-12. $1 \ amu = 1.66056 \times 10^{-24} \ g$.
Average Atomic Mass: Weighted average of isotopic masses based on their natural abundance.
- Average atomic mass $= \sum (\text{fractional abundance of isotope} \times \text{isotopic mass})$
Molecular Mass: Sum of the atomic masses of all atoms in a molecule.
Formula Mass: Sum of atomic masses of all ions in a formula unit of an ionic compound. (Used for ionic compo