Chemistry in general

• Atom


  The smallest particle of a substance that can exist
• Element


  Contains only one type of atom and cannot be split by chemical means
• Compound


  Two or more elements chemically combined, cannot be separated back into constituent elements
• Mixture


  Contains two or more elements not chemically combined, can be separated
• Atoms contain protons, neutrons and electrons
• Proton


  Positively charged particle in the nucleus
• Neutron


  Neutral particle in the nucleus
• Electron


  Negatively charged particle orbiting the nucleus
• Atomic number


  Number of protons in the nucleus
• Mass number


  Total number of protons and neutrons in the nucleus
• Group number


  Number of electrons in the outer shell
• Period number

  Number of electron shells
• Elements in the same group have similar chemical properties due to the same number of outer shell electrons
• Noble gases

  Group 0 elements that are highly unreactive due to full outer shells
• Isotopes


  Atoms of the same element with the same number of protons but different number of neutrons
• Ion

  A charged particle formed by gaining or losing electrons
• Ionic bonding

  1. Metal atom loses electron(s)

  2. Non-metal atom gains electron(s)

  3. Oppositely charged ions are attracted
• Covalent bonding

  Atoms share pairs of electrons to achieve full outer shells
• Covalent bonding examples


  • Water (H2O)
  • Methane (CH4)
• Water (H2O) has a central oxygen atom with two hydrogen atoms coming to the side
• Hydrogen


  Has one electron in its outer shell
• Oxygen


  Has six electrons in its outer shell, which becomes full with eight electrons
• Methane (CH4) has a central carbon atom with four hydrogen atoms
• Carbon dioxide (CO2) has double covalent bonds
• Ethene (C2H4) has a central carbon-carbon bond with four hydrogen atoms
• Giant ionic structure

  Made up of a metal and a non-metal, held together by strong electrostatic forces of attraction between oppositely charged ions
• Giant ionic structures

  • Have high melting and boiling points due to strong electrostatic forces requiring a lot of energy to break
  • Don't conduct electricity when solid as the ions aren't free to move
  • Conduct electricity when molten/liquid as the ions are free to move
  • Are brittle and smash easily when hit as the layers of ions with the same charge repel each other
• Giant covalent structures (diamond and graphite)

  • Have high melting points due to many strong covalent bonds requiring a lot of energy to break
  • Graphite is used as a lubricant as the layers of carbon atoms are weakly bonded and can slide over each other
  • Diamond doesn't conduct electricity as it has no free electrons, but graphite does conduct as it has a fourth free electron per carbon atom
• Covalent bond


  A shared pair of electrons between atoms
• Simple molecular substances


  • Have low melting points due to weak intermolecular forces that require little energy to break
  • Have increasing boiling points with increasing relative molecular mass (Mr) as greater intermolecular forces need more energy to overcome
• Giant metallic structures


  • Have high melting points due to strong metallic bonds between positive metal ions and a sea of delocalized electrons
  • Are good conductors of heat and electricity due to the delocalized electrons that are free to move
  • Are malleable and ductile as the layers of metal ions can slide over each other
• Balancing chemical equations


  1. List the elements on each side

  2. Make a tally chart to count the number of each element

  3. Adjust the coefficients to balance the equation
• Relative atomic mass (Mr) is the ratio of the average mass of an element compared to one atom of carbon-12
• Calculating moles


  Use the formula: moles = mass / Mr
• Empirical formula


  The simplest whole number ratio of atoms of each element in a compound
• Molecular formula


  The actual number of atoms of each element present in a compound
• Determining empirical formula from percentage composition

  1. List the elements and their masses

  2. Calculate the number of moles of each element

  3. Divide the moles by the smallest value to get the simplest ratio
• Calculating the value of x in a hydrated salt formula

  1. Set up a table with the anhydrous salt, water, mass, Mr, and moles

  2. Use the mass of the anhydrous salt and the mass remaining after heating to calculate the moles of water lost

  3. Divide the moles of water by the moles of the anhydrous salt to get the value of x
• ave a look at those three numbers and then choose the smallest one and divide all the values by the smallest number and as we can see that will be 3 3 so we're dividing every single value by 3.33 to get our ratio of 1 to 2 to 1
• now don't forget to answer the question we're looking for a formula so we have a final formula which is ch2o