Chemistry - Elements, Compounds, and Mixtures

An Element is a pure substance that consists of only one type of atom and cannot be broken down into simpler substances by chemical means. For example, Iron ($Fe$) and Oxygen ($O_2$).

A Compound is a substance formed when two or more different elements are chemically bonded together in a fixed ratio. Examples include Water ($H_2O$) and Sodium Chloride ($NaCl$).

A Mixture consists of two or more substances (elements or compounds) that are physically mixed but not chemically combined. The components retain their individual properties and can be separated by physical methods like filtration or distillation.

Molecules can be elements (e.g., $O_3$, $P_4$) if they contain only one type of atom, or compounds (e.g., $CH_4$) if they contain different types of atoms.

Compounds have a fixed composition by mass, represented by a chemical formula like $CO_2$, whereas mixtures can have varying compositions, such as air (mostly $N_2$ and $O_2$).

Pure substances (elements and compounds) have sharp, specific melting and boiling points, while mixtures melt or boil over a range of temperatures.

Chemical symbols represent elements (e.g., $Mg$ for Magnesium), and chemical formulae represent the number of atoms of each element in a unit of a substance (e.g., $H_2SO_4$ contains $2$ Hydrogen, $1$ Sulfur, and $4$ Oxygen atoms).