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

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