Some Basic Concepts of Chemistry - Properties of Matter and their Measurement

Matter is defined as anything that possesses mass and occupies space. It exists in three physical states: solid, liquid, and gas, which are interconvertible by changing conditions of temperature and pressure.

Physical properties are those which can be measured or observed without changing the identity or the composition of the substance, such as color, odor, melting point, and boiling point.

The International System of Units (SI) defines seven base units: length (meter, $m$), mass (kilogram, $kg$), time (second, $s$), electric current (ampere, $A$), thermodynamic temperature (kelvin, $K$), amount of substance (mole, $mol$), and luminous intensity (candela, $cd$).

Mass is the amount of matter present in a substance and is constant, while weight is the force exerted by gravity on an object and can vary with location.

Density is the amount of mass per unit volume. Its SI unit is $kg \cdot m^{-3}$, but it is frequently expressed in $g \cdot cm^{-3}$ in laboratory work.

Temperature is measured using three common scales: Celsius ($^\circ C$), Fahrenheit ($^\circ F$), and Kelvin ($K$). The Kelvin scale is the SI unit and does not use the degree symbol.

Scientific notation is used to express very large or very small numbers in the form $N \times 10^n$, where $N$ is a number between $1.000...$ and $9.999...$ and $n$ is an exponent.

Significant figures are meaningful digits which are known with certainty plus one which is estimated or uncertain. They reflect the precision of a measurement.