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Bonding. Formulas. Chemical formulas Tell us what elements a compound contains and the exact number of the atoms of each element in a unit of that compound Examples: SiO 2 1 atom of Silicon 2 atoms of Oxygen CH 3 COOH 2 atoms of Carbon 4 atoms of Oxygen 2 atoms of Oxygen.

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formulas
Formulas
  • Chemical formulas
    • Tell us what elements a compound contains and the exact number of the atoms of each element in a unit of that compound
  • Examples:
    • SiO2
      • 1 atom of Silicon
      • 2 atoms of Oxygen
    • CH3COOH
      • 2 atoms of Carbon
      • 4 atoms of Oxygen
      • 2 atoms of Oxygen
electron dot structures
Electron Dot Structures
  • Show only the electrons in the outer energy level of an atom
    • Electrons also called valence electrons
  • Chemical symbol surrounded by dots representing its outer electrons
how do you know how many dots to make
How do you know how many dots to make?
  • Group 1 – 1 outer electron
  • Group 2 – 2 outer electrons
  • Group 3 – 12 – varies
  • Group 13 – 3 outer electrons
  • Group 14 – 4 outer electrons
  • Group 15 – 5 outer electrons
  • Group 16 – 6 outer electrons
  • Group 17 – 7 outer electrons
  • Group 18 – 8 outer electrons
chemical stability
Chemical Stability
  • An atom is chemically stable when its outer energy level is complete.
  • Atoms need 8 electrons to become stable.
    • Exception – Hydrogen and Helium need only 2 electrons.
  • Noble gases
    • Stable since they have a complete outer energy level
chemical bonding
Chemical Bonding
  • Atoms with partially stable outer energy levels can gain, lose, or share electrons to obtain a stable outer energy level.
  • They combine with other partially stable outer energy levels to get 8 electrons
    • They become stable.
  • An attraction forms between the atoms, pulling them together to form compounds
  • Chemical bonds – the force that holds atoms together in a compound
slide7
Ions
  • Atoms lose or gain electrons which are called ions.
  • Ion
    • Charged particle since it has more of fewer electrons than protons
    • Loss of electrons – more protons
      • Called cations
    • Gain of electrons – less protons
      • Called anions
ionic bonding the givers and takers
Ionic Bonding – The Givers and Takers
  • Transfer of electrons between a metal and a nonmetal
    • Metals – lose electrons and become a positive ion
    • Nonmetals – gain electrons and become a negative ion
  • The positive charge of the metal and the negative charge of the atom must be balanced.
    • The compound is neutral.
covalent bonding the happy couple
Covalent Bonding – The Happy Couple
  • The sharing of electrons between two nonmetals
  • This sharing of electrons is called covalent bonding.
  • Types of bonds
    • Single bond – 2 shared electrons or 1 pair of electrons between atoms
    • Double bond – 4 shared electrons or 2 pairs of electrons between atoms
    • Triple bond – 6 shared electrons or 3 pairs of electrons between atoms
metallic bonding sea of electrons
Metallic Bonding – “Sea of Electrons”
  • The positively charged metallic ions are surrounded by a cloud of electrons
    • Metallic ions are positively charged since metals tend to lose electrons.
  • Electrons move freely among the positively charged ions
unequal sharing
Unequal Sharing
  • Electrons are not always shared equally between atoms in a covalent bond.
  • Strength of the attraction is related to
    • the size of the atom
    • the charge of the nucleus
    • the total number of electrons the atom has
  • Electrons that are unequally shared are held more closely to the atoms with the larger nucleus.
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