Matter and Atoms

Atoms are the basic building blocks of matter. Each element is made of one type of atom. Hydrogen has the simplest atom with just one proton and one electron.

Acids have a pH below 7 and taste sour, while bases have a pH above 7 and feel slippery. A pH of 7 is neutral, like pure water.

Molecules form when two or more atoms bond together. A water molecule has two hydrogen atoms bonded to one oxygen atom, written as H₂O.

A compound's properties differ from its elements. Sodium is a reactive metal and chlorine is a toxic gas, but together they form sodium chloride—common table salt.

Phase diagrams show how temperature and pressure affect the state of matter. Water's triple point is where solid, liquid, and gas phases all exist simultaneously.

Plasmas form when gases are heated to extremely high temperatures, stripping electrons from atoms. Stars, lightning, and neon signs all contain plasma.

Sublimation happens when a solid turns directly into a gas without becoming a liquid first. Dry ice (frozen carbon dioxide) sublimes at room temperature, and mothballs slowly shrink and vanish the same way.

Viscosity measures how easily a liquid flows. Thick liquids like honey and syrup have high viscosity and pour slowly, while thin liquids like water have low viscosity and flow quickly.

Atoms join in two main ways. In an ionic bond, one atom transfers electrons to another, as in table salt, while in a covalent bond atoms share electrons, as in water.