chemistry

• Atoms: The Building Blocks of Matter

  • All substances are made of tiny particles of matter called atoms which are the building blocks of all matter
  • Each atom is made of subatomic particles called protons, neutrons, and electrons
  • The protons and neutrons are located at the centre of the atom, which is called the nucleus
  • The electrons move very fast around the nucleus in orbital paths called shells
  • The mass of the electron is negligible, hence the mass of an atom is contained within the nucleus where the protons and neutrons are located
• The structure of the Carbon atom

  
• Element

  A substance made of atoms that all contain the same number of protons and cannot be split into anything simpler
• If you had 500g of pure carbon and divided it into 500 x 1g piles, each pile would contain the same substance and would not differ from any other pile
• Elements

  • Hydrogen
  • Carbon
  • Nitrogen
• The most recent Periodic Tables commonly contain around 103 elements although some go up to 118 elements
• Chemical symbol


  A unique representation of an element as seen on the Periodic Table
• Where a symbol contains two letters, the first one is always written in uppercase letters and the other in lowercase e.g., sodium is Na, not NA
• Elements that exist in nature as two atoms joined together

  • H2
  • N2
  • O2
  • F2
  • Cl2
  • Br2
  • I2
• The atomic number and mass number are also shown on the periodic table
• The symbol key for Carbon as represented in the periodic table - C is the symbol for Carbon and 12 is the mass number and 6 is the atomic number

  
• The Periodic Table - Chemist's best friend!

  
• • You will be provided with a Periodic Table in your Chemistry exams
  • You need to be able to use the names and symbols for the first 20 elements in the table
  • You also need to be able to use the name and symbols of the elements in group 1, group 7 and any other elements specified in these notes
• Elements

  Take part in chemical reactions in which new substances are made in processes that most often involve an energy change
• Atoms

  Combine together in fixed ratios that will give them full outer shells of electrons, often producing compounds
• Compound

  A pure substance made up of two or more elements chemically combined and which cannot be separated by physical means
• The properties of compounds are usually quite different from the elements that form them
• There is an unlimited number of compounds
• Chemical formula

  Tells you the ratio of atoms in a compound
• Chemical formula

  • H2O (2 hydrogen atoms and 1 oxygen atom)
  • NH3 (3 hydrogen atoms and 1 nitrogen atom)
• The chemical formula can be deduced from the relative number of atoms present
• Diagrams or models can also be used to represent the chemical formula
• The ammonia molecule consists of a central nitrogen atom bonded to 3 hydrogen atoms

  
• Non-metal only compounds

  • Covalent compounds contain only non-metals
  • They are named using prefixes (mono, di, tri, tetra, penta) to show how many of each element is present in the formula
  • For example, CO2 is carbon dioxide, NO is nitrogen monoxide and SiCl4 is silicon tetrachloride
  • A few covalent compounds are known by their common names, and you are expected to learn them, for example:
  • H2SO4 is sulfuric acid
  • NH3 is ammonia
  • CH4 is methane
  • HCl is hydrochloric acid (or hydrogen chloride if it is a gas)
  • C6H12O6 is glucose
  • C2H5OH is ethanol
  • HNO3 is nitric acid
• Naming compounds

  Depends on what type of elements make up a compound
• Types of compounds

  • Metals and non-metals
  • Ionic compounds
• Ionic compounds

  • Contain metal and non-metal elements joined together as particles called ions
  • The metal element's symbol is always written first
  • The non-metal element always takes on the name ending '– ide' unless oxygen is also present
• Ionic compounds

  • PbS is called lead sulfide
  • MgCl2 is called magnesium chloride
• Compounds with oxygen

  • The name ending is usually '-ate'
• Compounds with oxygen

  • CuSO4 is copper sulphate
  • KClO3 is potassium chlorate
  • Na2CO3 is sodium carbonate
• Some formula names are similar so be careful with spelling
• Similar formula names

  • NaNO3 is sodium nitrate
  • NaNO2 is sodium nitrite
• '-ite' ending


  Always has less oxygen than '-ate'
• The number of oxygen atoms varies, so you cannot tell how many oxygen atoms are present from the name ending
• Word Equations

  Show the reactants and products of a chemical reaction using their full chemical names
• Reactants

  Substances on the left-hand side of the arrow, the chemical ingredients of the reaction
• Products

  New substances on the right-hand side of the arrow
• Arrow

  Implies the conversion of reactants into products, spoken as "goes to" or "produces"
• Reaction conditions or catalyst

  Can be written above the arrow
• Reaction of sodium hydroxide and hydrochloric acid

  • Sodium hydroxide + hydrochloric acid ⟶ sodium chloride + water