The Nature of Substances and Chemical Reactions

• Atoms -

  • Protons are in the nucleus
  • Neutrons are in the nucleus
  • Electrons are in the orbit
• IONS - Gains or loses an electron = ion

  • Gains electron = negative ion
  • Loses electron = positive ion
• Diatomic elements - In the periodic table, those whose atoms travels in pairs are diatomic

  [H2 N2. O2. F2. Cl2. Br2]

  ALWAYS 2
• The boxes highlighted in pink are the non metals the rest are metals

  
• What the numbers by the atom in the periodic table means

  • top number is Mass Number
  • Bottom number is the Atomic Number

  
• How to calculate the NUMBER OF NEUTRONS

  • Mass number - Atomic number = Number of neutrons

  e.e. Sodium - Mass number (top number) = 23 - Atomic number (bottom number) = 11

  23-11=12. - 12 =number of Neutrons
• Atomic number (small / bottom number) = number of protons = number of electrons
• Mass number (big / top number) = number of protons + number of neutrons
• Isotopes - atoms of the same element with different numbers of neutrons. ( NEUTRONS ONLY )
• Isotopes - atomic numbers must be the same otherwise they are different elements
• Isotopes - EXAMPLE - Hydrogen isotopes : H1, H2, H3

  Atom version—->

  WHEN DEFINING WHAT AN ISOTOPE IS !USE AN EXAMPLE!

  
• Element or Compound - ELEMENT

  = H2 = 2 atoms of Hydrogen
• Element or Compound - COMPOUND

  = Co2 = 1 atom of Carbon

  2 atoms of Oxygen
• Compound Ions - LITHIUM FLUORIDE

  (1) Symbol = Li F

  Ion Charge = 1+ 1- They cancel out

  Ratio = 1 1

  Formula = LiF
• Mr - example - Mr for Water (H2O)

  H=1 (2 atoms) 1+1=2

  O=16

  2+16=18

  18 = Mr of H2O
• The Percentage Composition of COMPOUNDS

  Calculate % of Oxygen Fe2O3

  Fe = 56 O = 16

  (56x2) + (16x3) = 160 <—- Mr

  112 48

  (16x3)

  —-—— X 100 = 30%

  160