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