An anion is a negative ion because it gains electrons
A cation is a positive ion because it has lost electrons
Ionic bonding is bonding between a non-metal and metal by the transfer of electrons
Ionic compounds:
lattice structure
held together by strong forces of attraction between oppositely charged ions
form crystals because of lattice structure
Ionic compounds are formed by the loss and gain of electrons
Al3+ + O2- = Al2O3
Properties of ionic compounds:
very highmelting and boiling points
only conduct when molten or aqeous
soluble
lattice structure
Electrical conductivity of ionic compounds:
Do not conduct when in a solid state but heating them up to molten state or putting them in an aqueous solution breaks the electrostatic forces of attraction between the ions so the electrons are free to move and carry a charge
Ionic compounds have high boiling points because lots of energy is needed to overcome the strong electrostatic forces of attraction between the oppositely charged ions
Covalent bonds are formed between non-metals that share pairs of electrons in order to get full outer shells
Forms MOLECULES
Valency = the number of covalent bonds formed by atoms of different elements
Hydrogen, oxygen and chlorine go around in pairs, sharing electrons
Examples of molecular compounds are
Water (H2O), H-O-H
Hydrogen chloride (HCl), H-Cl
Cardon dioxide (CO2), O=C=O (double)
Properties of molecular compounds:
weak intermolecular forces
low melting and boiling points
cannot conduct electricity
Molecular compounds have low m&bp as the forces don't take much energy to overcome
Polymers are chains or small simple molecules (monomers), longer chains have stronger intermolecular forces, usually contain carbon atoms
Examples of polymers:
Poly (ethene)
Poly (styrene)
An allotrope is a different structural form of the same element]
DIAMOND:
Structure - giant covalent, tetrahedral arrangement, 4 bonds per atom
Properties - hard, high melting and boiling points, electrical insulator, strong covalent bonds
Uses - cutting heads when drilling rocks (very hard)
GRAPHITE:
Structure - giant covalent, hexagonal layered structure, weak forces between layers, 3 bonds per atom
Properties - soft, high melting and boiling points, electrical conductor, cheap, unreactive, strong covalent bonds
Uses - lubricant (layers slide past each other)
Graphite conducts electricity because not all of the electrons are held in bonds, some are delocalised and free to carry a charge
GRAPHENE:
Structure - not a simple molecule, sheet of carbon atoms, 1 atom thick
Properties - lightest known material, electrical conductor, very strong covalent bonds
Uses - can be rolled into a tube
FULLERENES: Molecules made up of carbon atoms only, with hollow shapes
Structure - simple molecules, often tubular or spherical
Properties - low melting and boiling points, soft and slippery, 3 bonds per atom, weak intermolecular forces, strong covalent bonds
E.G C60 (bucky ball)
Metal structure:
lattice of positive ions
sea of delocalised electrons
packed closely together in layers
Metals are malleable because the layers of ions slide over each other but the sea of electrons hold the ions together so instead of breaking the metal changes shape
Metals are conductors because the electrons are delocalised and free to move this means they can carry a charge and form an electric current and flow towards the positive terminal
Properties of metals:
malleable
good conductors
shiny when polished
high melting and boiling points
Metallic bonding is the electrostatic attraction between delocalised electrons and the positive metal ions
An acid is a substance that has a pH less than 7 and produces excess H+ ions in water
An alkali is a substance with a pH more than 7 and that produces excess OH- ions in water
Hazard symbols are important because:
universal, no language barrier
indicates the danger of the substance
gives information about how to work safely with the substance
An indicator is a substance that changes colour depending on the pH of a solution
Main acids:
HCl - hydrochloric
H2SO4 - sulfuric
HNO3 - nitric
CH3COOH - ethanoic
Main alkalis:
sodium hydroxide - NaOH
calcium hydroxide - CaOH2
potassium hydroxide - KOH
ammonium hydroxide - NH4OH
Universal indicator goes red in acid and blue in alkalis
Litmus paper goes red in acids and blue in alkalis
Phenolphthalein goes pink in alkalis and colourless in acids
Methyl orange goes red in acids and yellow in alkalis
If the concentration of H+ ions is increased by a factor of 10, the pH decreases by 1 and vice versa
A concentrated acid is one thst has a lot of solute dissolved per unit volume/ has a high concentration of H+ ions