Chemistry

• Balanced chemical equation


  A chemical equation written using the symbols and formulae of the reactants and products, so that the number of units of each element present is the same on both sides of the arrow
• Reactant


  A substance that reacts together with another substance to form products during a chemical reaction
• Product


  A substance formed in a chemical reaction
• State symbol


  A symbol used in chemical equations to show if a substance is a solid, a liquid, a gas, or an aqueous solution
• State symbols are useful because they show what a substance is like
• Conservation of mass


  The total mass of reactants before a reaction is equal to the total mass of products after a reaction, because no atoms can be created or destroyed so the mass must remain unchanged
• Atom


  The smallest part of an element that can exist
• Mass


  The amount of matter an object contains. Mass is measured in kilograms (kg) or grams (g)
• Balancing an equation


  1. Check to see if there are an equal number of atoms of each element on both sides

  2. Add numbers to the left of one or more formulae to balance the equation

  3. Check again to see if there are equal numbers of each element on both sides

  4. Add the state symbols if asked to do so
• Balanced chemical equations only show formulae, not names
• A balancing number, written in normal script, multiplies all the atoms in the substance next to it
• Atom


  The smallest part of an element that can exist
• Atoms


  • Consist of a nucleus containing protons and neutrons, surrounded by electrons in shells
• Proton


  Subatomic particle with a positive charge and a relative mass of 1
• Neutron


  Uncharged subatomic particle, with a mass of 1 relative to a proton
• Electron


  Subatomic particle, with a negative charge and a negligible mass relative to protons and neutrons
• Atom


  Consists of a nucleus containing protons and neutrons, surrounded by electrons in shells
• Atomic number

  The number of protons in the nucleus of an atom
• Mass number


  The number of protons and neutrons in the nucleus of an atom
• Isotopes


  Atoms of the same element with the same number of protons but different numbers of neutrons
• Relative atomic mass


  The mean relative mass of the atoms of the different isotopes in an element. It is the number of times heavier an atom is than one-twelfth of a carbon-12 atom.
• Isotope


  Atoms of an element with the same number of protons and electrons but different numbers of neutrons
• Isotopes

  • Have the same atomic number
  • Have different mass numbers
• The carbon-12 atom, \(_{6}^{12}\textrm{C}\) is the standard atom against which the masses of other atoms are compared
• Isotopes of an element have the same chemical properties
• Atomic number


  The number of protons in the nucleus of an atom
• Calculating relative atomic mass

  1. Multiply the mass number of each isotope by its abundance

  2. Add up the total mass of all isotopes

  3. Divide the total mass by the total number of atoms
• Mass number


  The number of protons and neutrons found in the nucleus of an atom
• Relative atomic mass

  The mean relative mass of the atoms of the different isotopes in an element
• Chlorine isotopes(chlorine-35)

  • \(_{17}^{37}\textrm{Cl}\) (chlorine-37)
• Relative atomic masses can be found in the periodic table and have the symbol Ar
• Mass numbers are always whole numbers, but relative atomic masses are often rounded to the nearest whole number and are not whole numbers
• The relative atomic mass of an element is a weighted average of the masses of the atoms of the isotopes, taking into account the abundance of each isotope
• Chlorine-35 abundance is 75%, chlorine-37 abundance is 25%
• Calculating relative atomic mass of chlorine

  1. Multiply mass number of chlorine-35 by its abundance (75 x 35)

  2. Multiply mass number of chlorine-37 by its abundance (25 x 37)

  3. Add the two results (2625 + 925)

  4. Divide the total mass by the total number of atoms (3550/100)
• Relative atomic mass of chlorine is 35.5 (to 1 decimal place)
• Calculating relative atomic mass of copper

  1. Multiply mass number 63 by its abundance (69 x 63)

  2. Multiply mass number 65 by its abundance (31 x 65)

  3. Add the two results (4347 + 2015)

  4. Divide the total mass by the total number of atoms (6362/100)
• Relative atomic mass of copper is 63.6 (to 1 decimal place)