Chemistry Notes Part 1

  Chemistry Important Definitions.

v  Everything is made up of very tiny pieces called particles. The smallest particles, that we cannot break down further in chemical reactions, are called atoms. In many substances, the particles consist of two or more atoms joined together are called molecules. In other substances, the particles are atoms or groups of atoms that carry a charge called ions. Ions present in solution but do not take part in the reaction are called spectator ions. Positive ions are cations. Negative ions are anions.
v  The valency of an element is the number of electrons, atoms lose, gain or share in forming compounds.
v  An Ionic Bond is a strong electrostatic attraction between ions of opposite charge. A Covalent Bond is a pair of electrons shared to form noble gas electronic configurations. Metallic Bonds are electrostatic attraction between positive metal ions and a sea of delocalised electrons.
v  The particles mix and spread by colliding with other particles, and bouncing off in all directions is known as diffusion.
v  Reactants mixed in solution giving insoluble product is precipitation.
v  Water bonded into hydrated salts is called water of crystallisation.
v  Ice changes to water when warmed is called melting. Zero Degree Celsius is called the melting point.
v  Alloy is a mixture of metal with other element/s.
v  A heating curve shows how the temperature of a substance changes as you heat it up. The temperatures remain constant while water changes state. These temperatures are its melting and boiling points. A cooling curve shows how the temperature of a substance changes as you cool it down.
v  Particles settle to the bottom of a tank is sedimentation. Add something to make fine particles stick together is flocculation.
v  When the temperature of a gas increases, the volume increases. (T is directly proportional to V) An increase in pressure means a decrease in gas volume. (P is indirectly proportional to V)
v  Fertiliser is any substance added to soil to be fertile.
v  The lower the mass of its particles, the faster a gas will diffuse. The mass of a molecule is called its relative molecular mass (M_r). The relative atomic mass of an element, A_r, is the average mass of its isotope, compared to 1/12 the mass of an atom of carbon – 12.
v  Plant growth in water, with no dissolved oxygen is eutrophication.
v  An element contains only one kind of atom. A compound is made of atoms of different elements bonded together. A mixture contains different elements or compounds that aren’t bonded together. It is easier to separate them. If no new chemical substance is formed, a change is a physical change.
v  Protons, neutrons and electrons are called subatomic particles because they are smaller than the atom. Atoms with the same number of outer shell electrons react similarly. The number of protons in an atom’s nucleus is called the proton number or atomic number. Total number of protons and neutrons in the atom’s nucleus is called nucleon number or mass number. Protons and neutrons form the nucleus, so they are called nucleons. The arrangement of electrons is called the electronic configuration of an atom.
v  6.02 X 10²³ particles is the Avagadro’s constant.
v  Halogen displaces less reactive from halide solution.
v  Petroleum is a smelly mixture of hundreds of different compounds.
v  Hydrocarbon only consists of carbon and hydrogen.
v  Isotopes are atoms of the same element that have the same number of protons, but different numbers of neutrons.
v  Viscosity is a measure of a fluid’s resistance to flow. It catches fire easily, it is flammable. It evaporates easily, it is volatile.
v  Carbon-carbon bonds are single covalent bonds so alkanes are saturated.
v  Empirical formula shows the simplest ratio in which atoms combine to form a compound.
v  Molecular formula shows actual numbers of atoms that combine to form a molecule.
v  Two molecules join to form a large molecule with water is a condensation reaction.
v  A gain of oxygen is oxidation. The loss of electrons is oxidation. The rise in oxidation number is oxidation. Oxidation acts as a reducing agent. Oxidation in Anode.
v  A loss of oxygen is a reduction. The gain of electrons is reduction. The fall in oxidation number is reduction. Reduction acts as an oxidising agent. Reduction at Cathode.
v  Electrolysis is the decomposition of an ionic compound, when molten or in aqueous solution, by the passage of an electric current.
v  Exothermic reactions give thermal energy to the surroundings. Endothermic reactions take thermal energy from the surroundings.
v  Activation energy is the minimum energy that colliding particles must have to react (E_a). Overall change in energy during a reaction is enthalpy change.
v  Rate is a measure of change that happens in a single unit of time. Change in: Concentration, temperature, pressure, surface area, catalyst. Catalyst is a substance that increases the rate of reaction and is uncharged at the end of the reaction. It lowers the activation energy of a reaction. Enzymes are proteins made by cells to act as biological catalysts.
v  In a reversible reaction, you can change the direction of the reaction by changing the conditions. The reaction from left to right is a forward reaction. The reaction from right to left is a backward (reverse) reaction.
v  A reversible reaction in a closed system is at equilibrium when:
-       The forward and reverse reactions take place at the same rate.
-       The concentrations of reactants and products are no longer changing.
Change in: temperature, pressure, concentration, catalyst.
v  The process used to manufacture ammonia is called the Haber process. Temperature: 450 degrees Celsius, Pressure: 200 atm (20000 KPa), Catalyst: Iron.
v  The process used to manufacture sulfuric acid is called the Contact process. Temperature: 450 degrees Celsius, Pressure: 2 atm (200Kpa), Catalyst: Vanadium (V) Oxide.
v  Plastic that can be broken down by microbes is biodegradable.
v  Acids are non-metal compounds in water. Strong acid completely dissociates in solution. Weak acid partially dissociates in solution. Acids are proton donors.
v  Bases are oxides and hydroxides of metals. Bases are proton acceptors.
v  Alkalis are soluble bases. They are hydroxides.
v  Oxides are compounds containing oxygen and another element. Amphoteric oxide reacts with both acids and alkalis.
v  Neutralisation is a reaction that produces salt and water when a base reacts with acid.
v  Prevent rusting: Paint, grease, plastic, galvanising, sacrificial protection.
v  Tackle acid rain: low sulfur fuels, flue gas desulfurization, catalytic converter.
v  A functional group is an atom or group of atoms in a molecule that dictates how the compound will react.
v  Homologous series is a family of similar compounds that have the same functional group, so have similar chemical properties. All compounds have the same general formula. Each member differs by CH₂.
v  Substitution reaction where one atom or group of atoms are replaced by another atom or group of atoms. (Photochemical reaction)
v  Structural isomers are compounds with the same molecular formula, but different structural formula.
v  Ethene molecules are monomers. Cracking breaks molecules into smaller ones. Many monomers join to form a polymer.
v  Addition reaction turns an unsaturated alkene into a saturated compound. There is only one product formed.
v  Polymerisation reaction, thousands of small molecules join to make one large molecule. Polymers in skin and bones are collagen and proteins. Polymer in hair, and nails is keratin. Polymers in plants are starch and cellulose.
v  Addition polymerisation, double bonds in molecules break and the molecules add on to each other.
v  A solution is saturated when it can dissolve no more solute at a specific temperature. The paper showing separated substances is a chromatogram. The retention factor (R_f) of a compound is the same for a solvent under the same conditions.