unit 6: ionic and covalent compounds

Chemical Bonds:

  • a mutual attraction between the valence electrons of one atom and the protons in the nucleus of another atom

Ionic Bonding:

  • formed between atoms of metals and nonmetals

  • valence electrons are completely transferred from the metal atom to the non-metal atom

  • between atoms in ionic bonding, there is electrostatic attraction

  • there is a positive sphere of charge and a negative sphere of charge

Lewis Structures:

  • metal electron transferred to nonmetal

  • metal = positive

  • nonmetal = negative

  • completes octet!

Covalent Bonding:

  • formed between atoms of nonmetals with other nonmetals

  • valence electrons are shared in pairs between bonded atoms

  • pure covalent bonds [non polar covalent] ONLY occur between two identical atoms

    • BRINCLHOF!! - seven diatomic elements

    • even distribution of the bonding electron cloud

Polar Covalent Bonding

  • electrons are shared but not equally

  • many compounds have both characteristics of covalent and ionic bonding

  • electronegativity differences determine the balance of the character

  • the separation of charge …

    • the more electronegative element = a partial negative charge

    • the less electronegative element = a partial positive charge

  • dipole arrow (shows separation of charge in the molecule)

    • POSITIVE to NEGATIVE

Lewis Structure:

  • SHARES electrons

Metallic Bonding

  • valence electrons are shared among all the atoms of the substance

  • occurs when metals are bonded to themselves or mixed with other metals (ALLOYS)

Alloys & Examples

  • mixture of a metal with other metals or nonmetals

  • examples:

    • brass (copper and zinc)

    • bronze (copper and tin)

    • carbon steel (iron and carbon)

    • solder (lead and antimony)

    • stainless steel (iron, chromium, and nickel)

Formulas

  • differences in electronegativities helps us classify bonds

  • Ionic: EN >= 1.7

  • Polar Covalent: 1.6 >= EN >= 0.5

  • Nonpolar Covalent: EN < 0.5

  • electronegativity:

    • defined as the ability of an atom in a covalent bond to attract the bonding electron cloud to itself

    • trend: increases across periods; decreases down groups