Summary
Highlights
Covalent bonds within molecules are strong, but simple molecular substances have weak intermolecular forces between molecules. Melting or boiling these substances only requires breaking these weak forces, resulting in low melting/boiling points. For example, chlorine boils at -34°C. Larger molecules have more intermolecular forces, leading to higher melting/boiling points, as seen when comparing halogens like chlorine, bromine, and iodine. Simple molecular substances do not conduct electricity because they lack free electrons or charged molecules.
Giant covalent structures consist of vast numbers of non-metal atoms all covalently bonded in repeating lattices. Examples include diamond, graphite, and silicon dioxide. They are very strong and have high melting/boiling points because breaking them requires overcoming numerous strong covalent bonds. Generally, they do not conduct electricity, except for graphite, due to the absence of free charged particles even when molten.
Silicon dioxide, also known as silica and the main component of sand, is made of silicon and oxygen atoms in a 1:2 ratio. While not required to draw, recognizing its giant covalent structure is important.
Simple molecular substances are small molecules with strong internal covalent bonds but weak intermolecular forces between molecules. Giant covalent structures have all atoms covalently bonded in extensive, repeating lattices, making them much stronger with significantly higher melting and boiling points.
Non-metals can form covalent bonds by sharing electrons to achieve full outer shells. This leads to either simple molecular substances (like chlorine or ammonia) or giant covalent structures (like diamond, graphite, or silicon dioxide). The video will compare their properties.