Giant Molecular structure

Some substances consists of extremely large molecules or giant molecules. The molecules contains many hundreds and thousands of atoms covalently bonded with each other. We call this substances macromolecules.
E.g.: - Diamond, graphite, silicon (IV) oxide (silica)

Structure of Diamonds
• Each single crystal if a diamond is one giant molecule. carbon atom is bonded to other carbon atoms tetrahedrally.
• All the four outermost electrons in carbon atom are involved in the bond formation and there are no free electrons to move. therefore diamond does not conduct electricity.
• A lot if energy is required to break apart the strong covalent bonds between the carbon atoms, hence diamond has very high melting & boiling point.
• Diamond is the hardest substance known since the carbon atoms are not able to slide over each other due to strong covalent bonds.
• Diamond is a transparent, colourless crystal.

Structure of Graphite
• Graphite has a layered structure each carbon is bonded to three other carbon atoms in a hexagonal arrangement to form rings of regular hexagons. the different layers are held together by weak vanderwaal's force of attraction.
• Graphite has very high melting & boiling point. therefore a lot of energy is required to break apart the strong covalent bonds between the carbon atoms.
• It is a good conductor of electricity because each carbon atom uses only 3 out of 4 outer electrons for bonding with one free electron to conduct electricity.
• The weak vanderwaal's force between the layers enables layers to slide over each other. hence graphite is a soft substance.
• It is black, opaque and shiny solid.

Structure of Polythene
• Polythene is a plymer. It is made up of thousands of molecules called monomers joined together in long chains. The monomer used in making polythene is called ethene.
• Polythene has high melting point and does not conduct electricity.
• Polythene can be softened on heating and melting and set again when cooled.

Simple Molecular structure

• A simple molecular structure contains small molecules.
• Simple molecular structure are formed from only a few atoms.
• They have strong covalent bonds between the atoms with in a molecule, what have weak bonds between molecules is called as Vanderwaal’s force.
• These vanderwaal’s forces increase steadily with the increasing size of the molecules.
• Most of the simple molecular structures are liquids or gases under normal conditions.
• In simple molecular structures the forces between the molecules in the solid and liquid state are weak such that very little energy is needed to break up the structure.
E.g.: - Methane (CH4), Iodine (I2), Water (H2O), Carbon dioxide (CO2)

Structure of Methane
This is the tetrahedral shake of methane molecule. The carbon-hydrogen bond is a strong covalent bond. There is weak vanderwaal’s force is between the molecules of methane.

Structure of Iodine
Iodine has a crystal structure in which iodine molecules are packed together. The force between the molecules are weak so iodine is a flaky solid that sublimes if heated gently iodine crystals can be crushed easily.

Elements, Compounds & Mixtures

Elements:
• An element is made up of only one types of atom.
• Elements are substances that cannot be broken down chemically into smaller substances.
E.g.: - Carbon, Nitrogen, Oxygen, Calcium, Helium etc.

Compounds:
• A compound is made up of two or more different kinds of atoms chemically combined together.
E.g.: - Water, Hydrochloric acid, Carbon monoxide etc.

Mixtures:
Mixtures are the substances that are simply mixed together without any chemical reaction taking place between them. A mixture is made up of two or more elements or compounds physically combined together. The individual substances can be separated by physical means.
E.g.: - Air, Sea water etc.