OCR A-level Chemistry: Module 2

• Simple molecular lattice


  A three-dimensional structure of molecules, bonded together by weak intermolecular forces
• Induced dipole


  A dipole temporarily created in an otherwise non polar molecule induced by a neighboring charge.
• Instantaneous dipole


  An atom or a molecule can have all, most or majority of its electrons shifted to one side by random chance of the electron movements. When this happens a temporary dipole is created causing the side with more concentration of electrons to become more electronegative and the opposite relatively electropositive.
• Hydrogen bond


  A strong dipole-dipole attraction formed when the slightly positive hydrogen atom of a polar covalent bond in one molecule is attracted to the slightly negative atom of a polar covalent bond in another molecule. (N, O, F)
• Permanent dipole-dipole interactions


  Attractive forces between the permanent dipoles in different molecules
• London forces


  Attractive forces between induced dipoles in different molecules (induced dipole-dipole interactions)
• Intermolecular forces

  An attractive force between molecules. Intermolecular forces can be London forces, permanent dipole-dipole interactions or hydrogen bonding
• Permanent dipole


  A small charge difference that does not change across a bond , with positive and negative partial changes on the bonded atoms : the result of the bonded atoms having different electronegativites
• Dipole


  A separation in electrical charge so that one atom of a polar covalent bond, or one end of a polar molecule, has a small positive charge (delta plus) and the other has a small negative charge (delta negative)
• Polar molecule


  A molecule with an overall dipole, having taken into account any dipoles across bonds and the shape of the molecule
• Polar covalent bond


  A bond with a permanent dipole, having positive and negative partial charged=s on the bonded atoms
• Pure covalent bond


  A covalent bond with equal sharing of electrons between atoms
• Non-polar bond


  With no charge separation across a bond or in a molecule
• Electronegativity values

  A value assigned as a measure of the relative attraction of a bonded atom for the pair of electrons in a covalent bond
• Electronegativity

  A measure of the attraction of a bonded atom for the pair of electrons in a covalent bond
• Bond angle


  The angle between two bonds at an atom
• Dative Covalent Bond


  A shared pair of electrons in which the bonded pair has been provided by one of the bonding atoms only (dative bond)
• Lone pairs

  An outer shell pair of electrons that is not involved in chemical bonding
• Displayed formula

  A formula that shows the relative positioning of all the atoms in a molecule and the bonds between them
• Molecule


  The smallest part of a covalent compound that can exist while retaining its chemical identity, consisting of two or more atoms covalently bonded together
• Covalent bonding


  The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms
• Giant ionic lattice


  a three-dimensional structure of oppositely charged ions, bonded together by strong ionic bonds
• Ionic bonding


  The electrostatic attraction between positive and negative ions
• Blocks


  There a 4; s, p, d and f
• Sub-shells

  A group of orbitals of the same type within a shell
• Atomic orbitals


  A region around the nucleus that can hold up to two electrons with opposite spins
• Principal quantum number


  A number representing the relative overall energy of each orbital, which increases with distance from the nucleus. the sets of orbitals with the same n-value are referred to as electron shells or energy levels
• Reduction

  Gain of electrons or a decrease in oxidation number
• Oxidation


  Loss of electrons or an increase in oxidation number
• Redox reaction

  A reaction involving reduction and oxidation
• Oxidation number


  A measure of the number of electrons that an atom uses to bond with atoms of another element
• Burette


  A graduated glass tube with a tap at one end, for delivering known volumes of a liquid, especially in titrations

  
• Pipette


  A ​thin ​glass ​tube used ​for ​measuring or ​moving a ​small ​amount of ​liquid

  
• Volumetric flask


  A type of laboratory glassware used to prepare solutions.

  
• Titration


  A measured amount of a solution of unknown concentration is added to a known volume of a second solution until the reaction between them is just complete
• Alkali

  A type of base that dissolves in water to release OH- ions
• Salt


  The product of a reaction in which the H+ ions from the acid are replaced by metal or ammonium ions
• Neutralises


  The reaction between an acid and a base to produce a salt
• Base


  A compound that neutralises an acid to form a salt
• Weak acid


  An acid that dissociates only partially in solution