N5 Chemistry unit 1

• Rates of reaction


  1. Measure changes in mass, volume and other quantities

  2. Draw graphs

  3. Interpret graphs in terms of end-point, quantity of product, quantity of reactant used, effect of changing conditions
• Rates of reaction


  • Can be increased by increasing temperature
  • Can be increased by increasing concentration of a reactant
  • Can be increased by increasing surface area/decreasing particle size
  • Can be increased through the use of a catalyst
• Catalyst


  Substance that speeds up chemical reactions but can be recovered chemically unchanged at the end of the reaction
• Calculating average rate of a chemical reaction

  Use equation: average rate = change in quantity / change in time
• The rate of a reaction can be shown to decrease (due to decreasing concentration) over time by calculating the average rate at different stages of the reaction
• Periodic Table and atoms

  • Elements in the Periodic Table are arranged in order of increasing atomic number
  • The Periodic Table can be used to determine whether an element is a metal or non-metal
  • Groups are columns in the Periodic Table containing elements with the same number of outer electrons, indicated by the group number
  • Elements within a group share the same valency and have similar chemical properties because they have the same number of electrons in their outer energy levels
  • The electron arrangement of the first 20 elements can be written
• Atom


  Has a nucleus, containing protons and neutrons, and electrons that orbit the nucleus
• Protons


  Have a charge of one-positive
• Neutrons


  Are neutral
• Electrons


  Have a charge of one-negative and have virtually no mass
• Atomic number


  The number of protons in an atom
• In a neutral atom the number of electrons is equal to the number of protons
• Mass number


  The number of protons added to the number of neutrons in an atom
• Isotopes


  Atoms with the same atomic number but different mass numbers, or atoms with the same number of protons but different numbers of neutrons
• Nuclide notation


  Used to show the atomic number, mass number (and charge) of atoms (ions) from which the number of protons, electrons and neutrons can be determined
• Most elements have two or more isotopes. The average atomic mass has been calculated for each element using the mass and proportion of each isotope present. These values are known as relative atomic masses.
• Covalent bond


  Forms between non-metal atoms when two positive nuclei are held together by their common attraction for a shared pair of electrons
• Elements that exist as diatomic molecules through the formation of covalent bonds


  • H2
  • N2
  • O2
  • F2
  • Cl2
  • Br2
  • I2
• Shape of simple covalent molecules

  Depends on the number of bonds and the orientation of these bonds around the central atom. Can be linear, angular, trigonal pyramidal or tetrahedral.
• More than one covalent bond can be formed between atoms leading to double and triple covalent bonds
• Covalent substances


  • Can form either discrete molecular or giant network structures
• Covalent molecular substances


  • Have strong covalent bonds within the molecules and only weak attractions between the molecules
  • Have low melting and boiling points as only weak forces of attraction between the molecules are broken when a substance changes state
  • Do not conduct electricity because they do not have charged particles which are free to move
• Covalent network structures


  • Have a network of strong covalent bonds within one giant structure
  • Have very high melting and boiling points because the network of strong covalent bonds is not easily broken
  • Do not dissolve
  • Do not conduct electricity because they do not have charged particles which are free to move
• Ion


  Made when atoms lose or gain electrons to obtain the stable electron arrangement of a noble gas
• In general, metal atoms lose electrons forming positive ions and non-metal atoms gain electrons forming negative ions
• Ionic bond


  The electrostatic attraction between positive and negative ions
• Ionic compounds


  • Form lattice structures of oppositely charged ions with each positive ion surrounded by negative ions and each negative ion surrounded by positive ions
  • Have high melting and boiling points because strong ionic bonds must be broken in order to break up the lattice
  • Many are soluble in water as the lattice structure breaks up allowing water molecules to surround the separated ions
  • Conduct electricity only when molten or in solution as the lattice structure breaks up allowing the ions to be free to move
• Conduction in ionic compounds can be explained by the movement of ions towards oppositely charged electrodes
• Compound names


  • Derived from the names of the elements from which they are formed
  • Most compounds with a name ending in '-ide' contain the two elements indicated
  • The ending '-ite' or '-ate' indicates that oxygen is also present
• Writing chemical formulae for two element compounds

  Using valency rules and a Periodic Table
• Roman numerals in compound names

  Indicate the valency of an element
• Chemical formula of a covalent molecular substance

  Gives the number of each type of atom present in a molecule
• Formula of a covalent network


  Gives the simplest ratio of each type of atom in the substance
• Group ions


  Ions containing more than one type of atom
• Writing chemical formulae for compounds containing group ions

  Using valency rules and the data booklet
• Ionic formulae


  Give the simplest ratio of each type of ion in the substance and can show the charges on each ion
• In formulae, charges must be superscript and numbers of atoms/ions must be subscript
• Writing and balancing chemical equations


  Using formulae and state symbols
• Gram formula mass


  The mass of a mole of any substance, in grams (g)
• Calculating the mass of a mole of any substance


  Using relative atomic masses