PROPERTIES AND STRUCTURES OF SUBSTANCES

PROPERTIES AND STRUCTURES OF SUBSTANCES

Properties and Structure of Substances

The properties and structure of substances depend on the types of particles (atoms, molecules, ions) that make them up and how these particles are arranged. The physical properties of substances such as boiling point, melting point, solubility, and conductivity are influenced by the strength of the forces between these particles.

• Atomic Structure: Atoms are made up of protons, neutrons, and electrons. The protons and neutrons are in the nucleus, and the electrons orbit the nucleus in electron shells.

• Molecular Structure: In molecules, atoms are held together by chemical bonds. The most common bonds are covalent bonds (sharing of electrons) and ionic bonds (transfer of electrons).

2. Relative Atomic Mass (Ar)

Relative atomic mass is the weighted average mass of an atom of an element compared to the mass of an atom of carbon-12. The atomic mass of carbon-12 is taken as exactly 12 units. This value reflects the number of protons and neutrons in an atom of that element.

• Example: The relative atomic mass of oxygen is approximately 16. This means one atom of oxygen weighs 16 times more than 1/12 the mass of a carbon-12 atom.

3. Relative Molecular Mass (Mr)

Relative molecular mass (also known as molecular weight) is the sum of the relative atomic masses of all the atoms in a molecule. It tells us how much heavier a molecule is compared to a carbon-12 atom.

6. Moles of a Gas and its Volume

The relationship between the number of moles of a gas and its volume is governed by the Ideal Gas Law, which states that at standard temperature and pressure (STP, 0°C and 1 atm), one mole of any ideal gas occupies a volume of 22.4 liters.