Elements compounds and mixtures

• Atom


  The smallest particle of a chemical element that can exist
• Atoms


  • argon (Ar), neon (Ne), helium (He)
• Element


  A substance made up of only one type of atom
• Elements


  • krypton (Kr), oxygen (O2), nitrogen (N2), sulfur (Ss)
• Molecule


  A particle made up of at least two atoms chemically bonded together
• Molecules


  • hydrogen (H2), carbon dioxide (CO2), water (H2O)
• Compound


  A substance made up of at least two different types of atom chemically bonded together
• Compounds


  • sodium chloride (NaCl), glucose (C6H12O6)
• Mixture


  A substance made from two or more different elements or compounds that are not chemically bonded
• Mixtures


  • air, sea water, a cup of tea
• All substances that exist as single atoms must be elements (only one type of atom). Molecules can be elements (e.g. oxygen, O2) or compounds (e.g. water, H₂O). Mixtures can contain atoms and/or molecules and elements and/or compounds.
• Very few elements exist on their own in nature (this is called the "native state) - they are mostly reacted with other elements to make compounds. One example of an element which does exist in the native state is gold, as it is very unreactive.
• Compounds have very different properties to the elements of which they are composed. Iron sulfide is a non-magnetic, black solid. Iron is a silvery magnetic metal. Sulfur is a brittle, yellow solid.
• Extracting Elements


  It is possible to split compounds up into their elements. However, this means that the chemical bonds in the compound have to be broken. Breaking chemical bonds requires large quantities of energy. This energy can be provided in the form of electricity.
• Electrolysis


  Splitting up compounds into elements using electricity
• Because electricity makes discovering more elements possible, more than half of the elements on the periodic table have discovered since the year 1800.
• Hofmann Voltameter


  A piece of equipment designed in 1866 by August Wilhelm von Hofmann for splitting water into hydrogen and oxygen.
• Hofmann Voltameter


  A dilute solution of sulfuric acid is electrolysed. The "cathode" and "anode" are made of platinum (an unreactive metal). The volume of hydrogen is twice the volume of oxygen.
• Some elements are man-made. This is true for all of the elements from number 95 (americium) to 118 (oganesson). Some others, such as technetium (number 43) are only found in tiny quantities, so are often produced synthetically.
• Groups


  Columns of elements on the periodic table. They are numbered from 1 to 7, then the last is numbered O. All of the elements in a group have similar chemical properties.
• Groups


  • Group 1- Alkali metals - all react with water and oxygen
  • Group 2 Alkali earth metals - all produce alkaline metal oxides
  • Group 7- Halogens - all have a similar distinctive "chlorine" smell
  • Group 0-Noble gases do not react at all
• Hydrogen (H) is a member of group 1, but it does not behave like the other elements in that group. It is often shown on its own at the top of the table.
• Periods


  Rows of elements on the periodic table. They show a repeating pattern (periodicity) in properties from left to right. The first period contains 2 elements (H and He), the second contains 8 (Li to Ne) and the third contains 8 elements (Na to Ar). Periods 6 and 7 actually contain 32 elements, but the "lanthanides" and "actinides" are usually taken out and placed under the rest of the table.
• Blocks


  Sections of the periodic table containing elements with some similar properties, but not as closely related as groups.
• Transition Elements


  The central block from scandium (Sc) in the top left corner to mercury (Hg) in the lower right.
• Metals and Non-metals


  Divided by a "staircase" or "zig-zag" line starting from between boron (B) and aluminium (Al). Some of the elements near the line, such as silicon (Si) are metalloids and display both metal and non-metal properties.
• Elements to Remember


  • Sodium, Na
  • Chlorine, Cl
  • Potassium, K
  • Bromine, Br
  • Magnesium, Mg
  • Copper, Cu
  • Lead, Pb
  • Hydrogen, H
  • Zinc, Zn
  • Iron, Fe
  • Iodine, I
  • Calcium, Ca
  • Nitrogen, N
  • Sulfur, S
  • Carbon, C
  • Oxygen, O
• Chemical Formula


  A convenient shorthand way of stating the types of elements and the number of atoms of each element present in a substance
• Numbers in Formulas


  The number of each element is written in subscript after the element symbol. If no number is shown, this means there is one of those atoms. If there are brackets, then the number of atoms inside the bracket is multiplied by the number after the bracket.
• We cannot change the number of each element in a compound - they are fixed for each different substance.
• Formulas


  • H2O is water; H₂Oz is hydrogen peroxide (bleach)
• Naming Salts


  If the compound contains two different elements, it ends "ide". If the compound contains two different elements and oxygen, it ends "ate". Salts are named with the metal first, then the non-metal part.
• Naming Salts


  • CuS copper sulfide, CuSO4 copper sulfate
• Naming Non-Salt Compounds


  Some compounds are not salts, but contain just non-metals. These can be trickier to name and so there are just a few common ones that you should memorise: Water, H₂O; Carbon dioxide, CO₂; Methane, CH4; Ammonia, NH3
• Balancing Equations


  In a chemical reaction, atoms cannot be made or destroyed. The atoms in a chemical reaction are only ever rearranged. This means that the number of each type of atom in the reactants must be the same as the number of each type of atom in the products.
• Balancing Equations


  We cannot change the subscript numbers in the formulas, so we must multiply each formula by a whole number until we get the same number of atoms on each side.
• Balancing Equations


  • H₂ Oz → H₂O, 2H₂ + Oz → 2H2O
• Although most equations can be solved quickly by trial-and-error, there are a couple of things you can attempt to speed up the process: For equations with metals, try balancing the metal atoms first. For equations with only C, H and O, balance the elements in that order.
• Metals


  • Good electrical conductor, good thermal conductor, strong, high melting point
• Non-Metals


  • Electrical insulator, thermal insulator, brittle, low melting point