Some Basic Concepts of Chemistry - Nature of Matter

Matter is defined as anything that has mass and occupies space. It can be classified physically into three states: Solid (fixed volume and shape), Liquid (fixed volume, no fixed shape), and Gas (no fixed volume or shape).

Chemically, matter is classified into Pure Substances and Mixtures. Pure substances consist of only one type of particles ($atoms$ or $molecules$) and include Elements (e.g., $Na$, $O_2$) and Compounds (e.g., $H_2O$, $CO_2$).

Mixtures contain two or more substances present in it in any ratio. They are either Homogeneous (uniform composition, e.g., sugar solution) or Heterogeneous (non-uniform composition, e.g., mixture of salt and sugar).

The International System of Units ($SI$) identifies seven base units: length ($m$), mass ($kg$), time ($s$), electric current ($A$), thermodynamic temperature ($K$), amount of substance ($mol$), and luminous intensity ($cd$).

Scientific notation is used to express numbers as $N \times 10^n$, where $1 \le N < 10$. For example, $232.508$ is written as $2.32508 \times 10^2$.

Significant figures indicate the precision of a measurement. Rules include: all non-zero digits are significant, zeros between non-zero digits are significant, and leading zeros are not significant.

Law of Conservation of Mass: In any chemical or physical change, the total mass of the products is equal to the total mass of the reactants.

Law of Definite Proportions: A chemical compound always contains exactly the same proportion of elements by mass, regardless of its source.

Law of Multiple Proportions: 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 the ratio of small whole numbers. Example: $H_2O$ and $H_2O_2$.

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 should contain an equal number of molecules.