Small molecules

• • Substances that have small covalent molecules are gases, liquid or solids with  low melting and boiling points 
  • They have strong covalent bondsbetween the atoms, but only weak forces between molecules
  • Examples include carbon dioxide and methane
• • They have relatively low melting and boiling points because: 
  • There are weak intermolecular forces between the molecules
  • These forces require little energy to overcome 
• • As the molecules increase in size, the melting and boiling points increase because the strength of these intermolecular forces increases and so more energy is needed to break them 
• • Substances that have small covalent molecules are poor conductors of electricity (even when molten) because there are no free ions or electrons to move and carry the charge
• • Most covalent compounds do not conduct at all in the solid state and are thus insulators
  • Common insulators include the plastic coating around household electrical wiring, rubber and wood

  
• Substances consisting of small covalent molecules have two types of bonds:

  • Covalent bonds- found between the atoms
  • Intermolecular forces -found between the molecules
• diagram of covalent and intermolecular bonds

  
• When a covalent molecule melts or boils the covalent bonds do not break, only the intermolecular forces. 
• Small molecules are two or more atoms covalently bonded together
• They are gas at room temperature because of low melting and boiling point
• small covalent molecules are also known as simple molecular substances