Chem

• what is water of crystallisation?

  water molecules that make up part of the crystal structure of a solid
• define relative isotopic mass


  the ass of an atom of an isotope of an element relative to one twelfth the mass of an atom of C-12
• why is relative atomic mass written as a decimal?

  it is a weighted average mass
• define molecular formula


  the actual number of atoms of each element in a compound
• define what an orbital is

  a region within an atom that can hold up to two electrons of opposite spins
• what shape are S orbitals?

  spherical
• what shape are orbitals?

  figure of 8
• how can you make out the electron structure of an element using the periodic table?

  period = energy level

  columns = electrons

  group = subshell
• show the oxidation of sodium and the reduction of chlorine

  Na -> Na+ + e-

  Cl + e- -> Cl-

  
  

  ions always go on the RHS whether oxidation or reduction
• define ionic bond

  the electrostatic force of attraction between positive and negative ions
• ionic bonding occurs between metals and non-metals but which ion is the exception?

  NH4+
• define covalent bond

  the strong electrostatic force of attraction between the shared pair of electrons and the nuclei of the bonded atoms
• when non-metals covalently bond, what is their aim?

  the octet rule:

  - to reach a noble gas configuration (8 electrons in the outer shell)
• what are there exceptions to the octet rule?

  - NO (odd number of electrons)

  - BF3 (boron has less than 8 outershell electrons)

  - SF6 (sulfur has more than 8 outershell electrons)
• why can sulfur have more than 8 electrons in its outershell?


  it has an empty 3d subshell
• define a dative covalent bond

  a shared pair of electrons which has been provided by only one of the bonding atoms
• give some common examples of ions with a dative bond

  NH4+

  H3O+
• what is a base?

  proton (H+) acceptors
• what is the shape of an atom determined by?

  - the number of electron pairs

  - electron pairs repel to become as far apart as possible

  - lone pairs of electrons repel more strongly than bonding pairs
• define electronegativity

  the ability of an atom to attract the bonding electrons in a covalent bond
• what creates a polar bond?

  - lone pairs offset symmetry by 102.5 degrees each

  - asymmetrical molecule

  - dipoles do not cancel out

  - bonded atoms with different electronegativities
• what are London forces?

  - uneven distribution of electrons causes a temporary dipole on one molecule

  - this induces an opposite dipole on the next molecule
• which type of molecules are London forces common to?

  - all molecules

  - however London forces are most obvious in nonpolar molecules
• what are permanent dipole-dipole forces?

  - the permanent dipole on one molecule will attract the opposite permanent dipole in a neighbouring molecule

  - this includes polar molecules
• what is hydrogen bonding?

  the attraction between the positive dipole on an H atom and the lone pair of electrons on an O, F or N on a different molecule
• between which type of molecules do intermolecular forces occur?

  simple covalent molecules
• give the properties of giant ionic compounds

  - high melting and boiling points as the lattice of strong ionic bonds requires a lot of energy to overcome

  - soluble in polar solvents as the ions interact with the dipole on water molecules

  - do not conduct when solid as the ions are fixed in place in the lattice

  - conduct when molten/aqueous solution as the ions are mobile
• why does boiling point increase down group 17?

  - the number of electrons in the molecules increase

  - larger dipoles are induced which means stronger London forces

  - more energy is required to overcome the intermolecular forces
• give the properties of simple covalent molecules

  - low melting and boiling points as intermolecular forces are weak

  - do not conduct as they have no mobile ions or delocalised electrons

  - nonpolar molecules will dissolve in nonpolar solvents
• why is ice less dense than water?

  - when water freezes a network of hydrogen bonds form which holds the H2O molecules apart in open lattice structure

  - this spacious lattice gives ice a lower density than water
• why does water have a RELATIVELY high boiling point?

  - between water molecules there are London forces as well as hydrogen bonds

  - a lot of energy is required to overcome these bonds
• give the general oxidation states

  group 1 element: +1

  group 2 element: +2

  group 3 element: +3

  fluorine: ALWAYS -1

  hydrogen: +1 (except with metals when it's -1)

  oxygen: -2 (except with F when it's +2)

  chlorine: -1 (except with O or F when it's positive)

  roman numerals: used to show the positive oxidation state of an element when it can have more than one oxidation state
• what is a concentrated solution?

  a solution which contains a high number of moles of solute dissolved in a given volume of solution
• give the ideal gas equation and its units

  PV=nRT

  P = pressure in Pa

  V = volume in m3

  n = moles

  R = 8.314

  T = temperature in K
• what is the relationship between atom economy and sustainability?

  low atom economy gives poor sustainability
• how is sustainability of a reaction increased?

  - find a use for waste products

  - develop an alternative process with a high atom economy

  - sell waste products
• what is an acid?

  a proton donor
• what is the formula for ethanoic acid?

  CH3COOH
• what are alkalis?

  bases that are soluble in water
• what is the ionic equation for neutralisation reactions?

  H+ + OH- = H2O