Chemical Bonding

Bonding and structure explains the properties of a substance! Overview Bonding Ionic Covalent Metallic Structure Giant ionic Simple molecular Giant covalent Giant Metallic Example Sodium chloride Water Diamond Iron Bonding and structure explains the properties of a substance!

Physical & Chemical Properties ‘property’: ‘what something is like’ Physical properties of a substance are those that can be observed or measured without the substance changing into another substance. Chemical properties of a substance describe the change of a substance into another substance. Some examples of physical properties: Solubility in water (or other solvents) Melting and boiling points Electrical conductivity

Ionic Bond: The Definition An ionic bond… is the force of attraction between opppositely charged ions in a compound.

Giant Ionic Structures Physical Properties: M.P. & B.P. Ionic compounds have high melting and boiling points. strong electrostatic forces of attraction between the ions in an ionic compound large amount of heat is needed to break the strong ionic bonds holding the ions together

Giant Ionic Structures Physical Properties: Electrical Conductivity Ionic compounds do not conduct electricity in the solid state. It conducts electricity in the molten and aqueous state. Why do ionic compounds only conduct electricity in the molten or aqueous state, but not in the solid state? ions can move in the molten or aqueous state moving ions carry the electric current

Giant Ionic Structures Physical Properties: Solubility Ionic compounds are soluble in water but insoluble in organic solvents. ions attract water molecules disrupts the crystal structure cause the ions to separate and go into solution

Giant Ionic Structures Physical Properties: Volatility Ionic compounds are not volatile and hence, have no smell. cannot evaporate easily because of strong ionic bonds holding the ions together A volatile substance evaporates easily.

Giant Ionic Structures Physical Properties: Physical State Ionic compounds are hard, crystalline solids. ions held in place by strong ionic bonds, make the crystal hard ions are arranged in straight rows and form structure with flat sides, resulting in a crystalline structure (flat sides & regular shapes)

Compare and Contrast

Ionic VS Covalent Ionic Bond Covalent Bond Similarities Differences Electronic configuration of a noble gas (PS: Everybody wants to be noble!!) Differences Ionic Bond Covalent Bond Between positive ions of metals and negative ions of non-metals Between non-metal atoms Electrons are transferred Electrons are shared

What to do??

Covalent Bonding

Covalent Bond: The Definition A covalent bond is… a bond formed by the sharing of a pair of electrons.

More about COVALENT BONDING Each atom acquires a stable octet structure Electronic configuration of noble gas (Full shell) = Energetically stable Formed between atoms of non-metals (but there are exceptions!) “Spectrum” of bonds

Simple Molecular Substances Consists of small molecules, e.g. bromine

Simple Molecular Substances Within the molecule Atoms are held together by strong covalent bonds Between molecules Weak intermolecular forces (van der Waals’ forces)

Iodine, I2 Within each iodine molecule, the iodine atoms are held together by strong covalent bonds. Between the iodine molecules, there are only weak van der Waals’ forces holding the molecules together.

Methane, CH4 In a molecule of methane, CH4, the four C–H covalent bonds are strong. However, weak intermolecular forces between methane molecules hold them together loosely. Therefore, methane exists as a gas at room temperature and pressure.

Physical Properties Physical state Low M.P. & B.P. Most substances are liquids or gases at room temperature. Forces between molecules are weak, allowing molecules to move freely. Low M.P. & B.P. Little energy required to overcome the (weak) intermolecular forces (Usually <200°C)

Melting & Boiling Points Covalent substance Melting point (C) Boiling point (C) Carbon dioxide -56 -79 Chlorine -101 -35 Hydrogen -259 -253 Methane -183 -161 Oxygen -214 Water 100

Physical Properties Volatility Electrical conductivity Solubility Low B.P. = Volatile Evaporate easily (to give a smell) Electrical conductivity Do not conduct electricity. (Some exceptions, e.g. graphite) No free-moving ions or electrons to conduct electricity Solubility Most molecular substances are insoluble in water, but dissolve in organic solvents. (Some exceptions, e.g. alcohol and sugar, hydrogen chloride)