Chemical Bonding Notes

Chemical bonding: the combining of atoms of elements to form new substances.
The electron arrangement of the outermost energy level determines whether or not the atom will form chemical bonds
Valence electrons: electrons in the highest occupied energy level of an element’s atoms
Electron dot structure: diagrams that show valence electrons as dots (around the symbol of the element)
Octet rule: in forming compounds, atoms tend to achieve the electron configuration of a noble gas
- 8 electrons in the highest occupied energy level
Duet rule: smaller atoms will achieve a stable electron configuration with only 2 electrons in their outermost energy level

Ionic bonding: bonding that involves a transfer of electrons (electrons are lost or gained)
- typically occurs when a metal bonds with a nonmetal
- because ionic bonding involves the transfer of electrons, one atom gains electrons and the other atom loses electrons
Ionic compounds: compounds composed of cations and anions
- are electrically neutral
  - total positive charge of the cations equals the total negative charge of the anions
- most are crystalline solids at room temperature
- generally have high melting points
- can conduct an electric current when melted or dissolved in water
- Ex: sodium chloride (table salt)

Covalent bonding: bonding in which electrons are shared
- shared electrons are in the outermost energy level of both atoms at the same time
- usually occurs when a nonmetal bonds with a nonmetal
Molecular compounds: compounds composed of molecules held together by covalent bonds
- molecules are atoms or groups of atoms joined together by covalent bonds
- have relatively lower melting and boiling points than ionic compounds
- can be solid, liquid, or gas at room temperature
- Ex: water ( $H_2O$ )

Metallic bonding: the attraction of free-floating valence electrons for the positively charged metal ions
- valence electrons of metal atoms can be modeled as a sea of electrons
  - valence e- can drift freely from one part of the metal to another
  - explains many physical properties of metals
    - ductile
    - malleable
    - conductive
Alloys: mixtures composed of two or more elements, at least one of which is a metal
- Ex: brass, stainless steel, sterling silver
- alloys are important because their properties are often superior to those of their component elements