chem

• Atom


  The smallest particle of an element that can take part in a chemical reaction
• Element


  A pure substance that cannot be split any simpler by any chemical means, made up of only one type of atoms
• Structure of an Atom

  • Central Nucleus
  • Energy levels / Energy Shells
• Sub-atomic particles in the nucleus

  • Protons (p+)
  • Neutrons (n°)
• Sub-atomic particles in the energy shells

  • Electrons (e-)
• Atomic Number


  The number of protons (p+) in the nucleus of an atom, the "fingerprint" of an element/atom
• Mass Number / Atomic Mass / Nucleon number


  The total sum of protons and neutrons (n°) in the nucleus of an atom
• An atom is said to be electrically neutral because the number of positive protons & negative electrons are always equal so the charges cancel out
• How elements/atoms in the periodic table are represented

  • Chemical Symbol
  • Mass number
  • Atomic number
• The Mass number is always greater than the Atomic number
• Isotopes


  Atoms of the same element, with the same atomic number but different mass number or number of neutrons
• Relative Atomic Mass (R-A-M)


  The mass of any atom compared to that of Carbon-12
• Calculating Relative Atomic Mass (R-A-M)

  1. Using % abundance

  2. Using ratios
• Isotopes have similar chemical properties because they have the same number of electrons in the outermost shell
• Ion


  A negatively or positively charged particle formed when an atom gains or loses electron(s) to become stable
• Rules for arranging electrons in the energy levels

  • 1st shell can hold max 2 electrons
  • 2nd, 3rd & 4th shells can each hold max 18 electrons
  • Start arranging electrons in the next shell if the previous one is fully filled
  • Always start from the 1st shell and arrange
• The first 20 elements of the periodic table

  • Hydrogen (H)
  • Helium (He)
  • Lithium (Li)
  • Beryllium (Be)
  • Boron (B)
  • Carbon (C)
  • Nitrogen (N)
  • Oxygen (O)
  • Fluorine (F)
  • Neon (Ne)
  • Sodium (Na)
  • Magnesium (Mg)
  • Aluminium (Al)
  • Silicon (Si)
  • Phosphorus (P)
  • Sulfur (S)
  • Chlorine (Cl)
  • Argon (Ar)
  • Potassium (K)
  • Calcium (Ca)
• Metals


  Atoms that react by losing electrons to form stable cations (positively charged ions)
• Non-metals


  Atoms that react by gaining electrons to form stable anions (negatively charged ions)
• Metalloids


  Atoms that can either gain or lose electrons
• Noble gases


  Atoms that are stable and unreactive, neither gaining nor losing electrons
• When an atom gains or loses an electron, it loses the same amount of energy in both processes
• An atom will always prefer the option of gaining/losing an electron where it loses the least energy
• Cation


  A positively charged ion formed when an atom loses electron(s)
• Anion


  A negatively charged ion formed when an atom gains electron(s)
• Atoms are electrically stable because the number of positive protons equals the number of negative electrons
• Gaining/increasing electrons makes an atom more negative, losing/decreasing electrons makes an atom more positive
• Valency


  The number of electrons an atom gains or loses to become stable
• Oxidation number/Oxidation state


  The number together with the charge, indicating the number of electrons gained or lost