Chem WA2

• Diamonds


  Have a three-dimensional giant covalent structure in a tetrahedral arrangement, where each carbon atom forms a covalent bond with four other carbon atoms
• Covalent bonds in diamond

  Strong and extensive, require large amount of energy to break
• Graphite


  Has high melting/boiling points due to large amount of energy required to break the strong carbon-carbon covalent bonds within the layers
• Graphite


  Conducts electricity as 3 out of 4 valence electrons of each carbon atom are used for covalent bonding, leaving 1 valence electron free to move within the graphite layers
• Graphite


  Insoluble in water and organic solvents
• Ionic bonding


  Results in a giant ionic crystal lattice - three-dimensional structure of alternating positive and negative ions, with electrostatic forces around them
• Covalent bond


  One bonding pair = one electron from each side
• Simple covalent molecules


  Small number of atoms, e.g. water
• Giant covalent molecules


  Uncountable atoms in each molecule, e.g. 1g of diamond contains 5.02 x 10^22 carbon atoms
• All ways an atom seeks to achieve valency above MUST have the atoms have a fully filled valence shell
• Metallic bonding


  Metals have free-moving electrons, which were lost by metallic atoms to achieve stability, forming a giant metallic lattice
• Solubility


  Insoluble in water but soluble in organic solvents: Polymers, simple covalent structures

  Insoluble in both water and organic solvents: Giant covalent structures, metallic structures

  Soluble in water and insoluble in organic solvents: Ionic substances
• Electrical conductivity


  Conductors in molten and aqueous states but not in solid: Ionic compounds

  Insulators (no matter the state): Simple and giant covalent structures (except hydrogen chloride and graphite), macromolecules (polymers)
• States at room temperature

  Ionic compounds: Solids

  Simple covalent structures: Liquids or gas

  Giant covalent structures: Solid

  Metallic compounds: Solid
• Simple Covalent substances


  • Softer and more flexible

  Insoluble in water and soluble in organic solvents

  Low melting and boiling points, most are volatile and exist mostly as gases or liquids

  Insulators, as do not have any mobile charge carriers (neutral molecules) but some can dissociate in water to form a solution that can conduct electricity
• Giant Covalent Substances


  • Diamond - hard, Graphite - soft and slippery

  Insoluble in water and in organic solvents

  Very high melting and boiling points

  Do not conduct electricity (except for graphite, which conducts electricity through layers)
• Macromolecules (polymers)


  • Hardness varies

  Insoluble in water and soluble in organic solvents

  Melting and boiling points not fixed

  Not able to conduct electricity in any states
• Ionic substances


  • Alternating positive and negative ions held together by electrostatic forces of attraction

  Hard but brittle

  Soluble in water and insoluble in organic solvents

  Very high melting and boiling points, solids at room temperature

  Unable to conduct electricity in solid state, but can conduct electricity in a molten or aqueous state
• Metals


  • Malleable and ductile, alloys stronger than pure metals

  Insoluble in both water and organic solvents

  Very high melting and boiling points

  Good conductors of heat and electricity
• Important alloys


  • Bronze: copper and tin

  Brass: Copper and zinc

  Steel: Iron and carbon
• Acids


  Substances that produce Hydrogen ions, H+, when ionised in water
• Properties of acids


  • Sour taste

  Produce free moving electrons when dissolved in water

  Turn blue litmus paper red

  React with reactive metals, metal carbonates and bases
• Important acids


  • Ethanoic Acid CH3COO

  Hydrochloric acid HCl

  Nitric acid NO3

  Sulfuric acid SO4
• Reaction of reactive metals with acids

  Metal + Acid → salt + hydrogen gas

  Effervescence

  Test: Place a burning split at the mouth of the test tube, hydrogen gas extinguishes the burning sprint with a 'pop' sound
• Unreactive metals


  Copper, Silver, Lead (layer of lead chloride/sulfate forms a coating around the metal)
• Reaction of bases with acids


  Base + acid → salt + water

  Neutralization, resulting mixture is neutral
• Reaction of carbonates with acids


  Carbonate + acid → salt + water + carbon dioxide

  Test: Bubbling the gas through limewater, carbon dioxide gas forms a white precipitate
• Alkalis


  Bases that ionise in water to produce hydrogen ions, OH-
• Properties of alkalis


  • Bitter taste

  Feel slippery and soapy

  Dissolve in water to form solutions that conduct electricity

  Turn red litmus paper blue
• Important alkalis


  • Sodium hydroxide NaOH

  Potassium hydroxide KOH

  Calcium hydroxide Ca(OH)2

  Ammonia NH3
• Reaction of alkalis with ammonium salts


  Alkali + ammonium salt → salt + water + ammonia

  Test: Pungent smell + damp red litmus paper turns blue at the mouth of the test tube
• Strong acid/alkalis


  Completely ionised in an aqueous solution (100% of acid molecules form ions)
• Weak acid/alkalis


  Partially ionised in an aqueous solution (less than 100% of acid molecules form ions)
• Oxides


  Compounds of oxygen and another element
• Basic oxides (most metals)

  • Mostly insoluble in water (except sodium oxide and potassium oxide)

  Solids at room temp

  React with acids to form salt + water
• Amphoteric oxides (Metallic)


  • React with both acids and bases to form salts and water

  Solubility varies (aluminum oxide and zinc oxide are both insoluble in water)
• Acidic oxides (non-metal)


  • Dissolve in water to form acids (soluble)

  Do not react with acids, but react with alkalis to form a salt and water

  State at room temperature varies
• Neutral oxides (non-metal)


  • Do not react with basic or acidic

  Insoluble in water (except for water itself)
• Acids and alkalis can both conduct electricity as both have free moving ions
• Most salts are neutral