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Ionic & Covalent Bonding

  • %%Lewis Dot Structure%%
    • represents electrons as dots in dot structures
    • the valence electrons of main-group elements are represented as dots surrounding the element symbol
    • dots are filled on all 4 sides before pairing - Helium is the only exception
    • ^^octet rule^^ - atoms with 8 valence electrons - which are particularly stable
    • exclusions: hydrogen, lithium, beryllium
    • achieve stability when it has 2 electrons in valence shell
    • chemical bonds involves the sharing or transfer of electrons to attain stable electron configuration
    • ^^ionic bond^^ - electrons are transferred
    • ^^covalent bond^^ - electrons are shared
    • stable configuration - eight electrons in the valence shell
  • ^^Ionic Bonds^^
    • metals bond with nonmetals - ==electrons are transferred== from the metal to the nonmetal
    • metal becomes a cation
    • nonmetal becomes an anion
    • attraction between cation + anion → ionic compound
    • metal/cation always comes first in the chemical formula
    • properties
    • generally crystalline solid at room temp
    • strong bond due to large attractive forces
    • high melting point due to strong bond
    • generally soluble in water
    • conduct electricity in molten or dissolved state because ions move freely
  • ^^Covalent Bonds^^ no ions
    • when nonmetals bond with other nonmetals
    • ==electrons are shared==
    • share valence electrons in order to attain octets
    • ==bonding pair electrons== : electrons shared between two atoms
    • ==lone pair / nonbonding== : electrons not involved in bonding
    • properties
    • generally gas at room temp
    • weaker bond than ionic compounds
    • low melting point due to weak bonds
    • generally insoluble in water
    • do not conduct electricity
  • ^^chemical formula^^ - shows the numbers of atoms of each element in the smallest representative unit of a substance
  • ^^formula unit^^ - the lowest whole number ratio of ions in an ionic compound
  • ^^Polyatomic Ions^^
    • molecule with a charge
    • atoms bonded covalently
    • metal has to be present during bonding
  • ^^Polarity^^
    • electronegativity - ability of an element to attract electrons within a covalent bond
    • ==dipole moment== - has a partial negative charge (δ-) and a partial positive charge (δ+)
    • result of uneven electron sharing
    • the element with the highest electronegativity has the partial negative charge
    • the magnitude of the dipole moment and the polarity of the bond depend on the electronegativity difference between the two elements in the bond
    • 0≤x≤.4 - nonpolar covalent
    • .4<x≤2.0 - polar covalent
    • 2.0≤x≤3.3 - ionic
    • if on 2.0 - depends on the presence of a metal
    • covalent bonds
    • polar - unequal sharing
    • nonpolar - equal sharing
    • flourine has the most electronegativity with 4.0
  • Predicting the Shape of Molecules - VSEPR
    • Valence Shell Electron Pair Repulsion
    • idea that electron groups - lone pairs + single/multiple bonds - repel each other
    • this repulsion between the negative charges of electron groups on the central atom determines the geometry of the molecule
  • transition metals can form multiple ions except
    • zinc +2
    • cadmium +2
    • silver +1