Chemistry Module 3

• Atomic (Proton) Number


  The number of protons in the nucleus of an atom
• Bohr Model


  Describes an atom as a small dense nucleus with electrons orbiting around the nucleus. This model explains different periodic properties of atoms.
• Cations


  Positively charged ions
• 1. block


  The part of the periodic table in which the elements have their highest energy electron in a d-orbital
• Electron Configuration


  The arrangement of electrons into orbitals and energy levels around the nucleus of an atom / ion
• First Ionisation Energy


  The removal of one mole of electrons from one mole of gaseous atoms. Factors which affect the first ionisation energy are: the strength of attraction between the electron and the nucleus, the nuclear charge and the atomic radius. There is a small decrease in first ionisation energy due to s- and p-subshell energies (between Be and B) and p-orbital repulsion (between N and O).
• Giant Covalent Lattice


  A network of atoms bonded by strong covalent bonds (e.g. carbon (diamond, graphite and graphene) and silicon). Giant covalent lattices typically insoluble with a high melting and boiling point due to the presence of strong covalent bonds. They are also poor electrical conductors as they don't contain mobile charged particles.
• Giant Metallic Lattice Structure

  The structure of all metals, made up of cations and delocalised electrons. Giant metallic structures are typically insoluble with a high melting and boiling points due to strong electrostatic forces of attraction between cations and electrons. Metals are good electrical conductors due to the presence of delocalised electrons (mobile charges).
• Group

  A column in the periodic table
• Melting Point


  The temperature at which a solid melts and becomes a liquid. This increases from giant metallic to giant covalent structures then decreases to simple molecular structures.
• Metallic Bonding


  Strong electrostatic attraction between cations and delocalised electrons
• 1. block


  The part of the periodic table in which the elements have their highest energy electron in a p-orbital
• Period


  A row in the periodic table
• Periodicity


  A repeating trend in physical and chemical properties across the periods of the periodic table
• 1. block


  The part of the periodic table in which the elements have their highest energy electron in an s-orbital
• Successive Ionisation Energies


  The energy required to remove each electron one-by-one from one mole of gaseous atoms / ions
• Base


  A substance that can accept H+ ions from another substance. Group 2 compounds can be used as bases: Ca(OH)2 is used to neutralise acidic soils in agriculture and Mg(OH)2 and CaCO3 are used as antacids to treat indigestion.
• Electron Configuration


  The arrangement of electrons into orbitals and energy levels around the nucleus of an atom/ ion. Group 2 elements have an s2 outer shell electron configuration.
• First Ionisation Energy


  The removal of one mole of electrons from one mole of gaseous atoms. Factors which affect the first ionisation energy are: the strength of attraction between the electron and the nucleus, the nuclear charge and the atomic radius.
• Group 2 Oxide


  A compound with the general formula MO, where M is a group 2 element. When group 2 oxides react with water, they form an alkaline solution, with alkalinity increasing down the group.
• Oxidation


  The loss of electrons / increase in oxidation number
• Redox

  A reaction in which oxidation of one element and reduction of another occurs. During a redox reaction involving group 2 elements, 2 electrons are lost to form 2+ ions. Group 2 elements undergo redox reactions with water, oxygen and dilute acids.
• Reduction


  The gain of electrons/ decrease in oxidation number
• Second Ionisation Energy


  The removal of one mole of electrons from one mole of gaseous 1+ ions to form one mole of 2+ ions
• Boiling Point


  The temperature at which a liquid boils and becomes a gas. Boiling point increases down group 7 due to the increasing strength of London Forces between the halogen molecules.
• Diatomic Molecules


  Molecules that are made up of 2 atoms. Halogens are diatomic.
• Displacement Reaction


  A reaction in which one atom is replaced by another. Halogens can undergo displacement reactions as their reactivity decreases down the group. The more reactive halogen will displace the less reactive halogen from a solution of its salt.
• Disproportionation

  The oxidation and reduction of the same element. Examples include the water treatment (reacting chlorine with water) and bleach formation (reacting chlorine with cold, dilute aqueous sodium hydroxide).
• Electron Configuration


  The arrangement of electrons into orbitals and energy levels around the nucleus of an atom / ion. The halogens have a s2p5 outer shell electron configuration.
• Induced Dipole-Dipole Interactions


  Forces of attraction between molecules caused when the random movement of electrons creates a temporary dipole in one molecule which then induces a dipole in a neighbouring molecule.
• London Forces


  Another name for induced dipole-dipole interactions.
• Precipitation Reaction


  A reaction in which two aqueous solutions are combined to form an insoluble salt (a precipitate). Halide anions undergo precipitation reactions with aqueous silver ions.
• Redox reaction

  A reaction in which oxidation of one element and reduction of another occurs. During a redox reaction involving group 7 elements, 1 electron is gained to form 1- ions.
• Water Treatment

  The addition of chlorine to water to kill bacteria. The risks associated with the use of chlorine to treat water are the hazards of toxic chlorine gas and the possible risks from the formation of chlorinated hydrocarbons.
• Anion


  A negatively charged ion
• Ammonium Ion

  An ion with the formula NH4+. The test for ammonium ions is a reaction with warm NaOH, which forms NH3.
• Cation


  A positively charged ion
• Carbonate


  A salt containing the CO32- anion. A reaction between a carbonate and H+ will form CO2(g).
• Halide


  A salt containing a group 7 anion. Cl-, Br- and I- can be tested for using a solution of silver ions as this reaction forms a coloured precipitate. The solubility of the precipitate is then tested using dilute and concentrated ammonia.
• Qualitative Analysis


  Identifies the elements present in a substance, typically using test-tube reactions.