6-2 Covalent Bonding & Molecular Compounds
· Molecule – a neutral group of atoms that are held together by covalent bonds
o EX:
· Molecular compound – A chemical compound whose simplest units are molecules
o EX:
· Chemical Formula – Indicates the relative numbers of atoms of each kind in a chemical compound by using atomic symbols and numerical subscripts
o EX:
· Molecular formula – Shows type and numbers of atoms combined in a single molecule of a molecular compound
o EX:
· Diatomic molecule – a molecule containing only two atoms
o EX:
Formation of a Covalent Bond:
· Nature favors ______ bonding because most atoms are at lower potential energy when bonded to other atoms that they are at as independent particles.
o See Figure 6-5 : The electron-proton attraction is stronger than the electron-electron and proton-proton repulsions, therefore the atoms are drawn to eah other and their potential energy is lowered.
Characteristics of the Covalent Bond:
· ______ - the distance between two bonded atoms at their minimum potential energy
o Average distance between 2 bonded atoms.
· ______ - the energy required to break a chemical bond and form neutral isolated atoms.
o Measured in ______
· Bond lengths and bond energies vary with the types of atoms that have combined
The Octet Rule:
Chemical compounds tend to form so that each atom,
by gaining, losing, or sharing electrons,
has ______electrons in its highest occupied energy level.
· ______ Elements – inert; 8 valence electron provide stability (except helium)
· S and P orbitals are completely filled with eight electrons by sharing electrons
· Exceptions: Hydrogen, boron, BF3
o Other elements can be surrounded by more than eight electrons when they combine with the highly electronegative elements fluorine, oxygen, and chlorine.
Electron- Dot Notation:
· ______ an electron-configuration notation in which only the valence electrons of an atom of a particular element are shown, indicated by dots place around the element’s symbol.
o EX: Fluorine, Hydrogen, Nitrogen
Lewis Structures:
Formulas in which atomic symbols represent nuclei and inner-shell electrons
· Dot-pairs or dashes between 2 atomic symbols represent electron pairs in covalent bonds
· Dots adjacent to only one atomic symbol represent unshared electrons called ______.
o EX: H2, F2
Rules:
1. Determine the type & number of atoms in the molecule
2. Write the electron-dot notation for each type of atom in the molecule
3. Determine the total number of valence electrons in the atoms to be combined
4. Arrange the atoms to form a skeleton structure for the molecule, and connect the atoms by electron-pair bonds
a. If carbon is present, then it will be the central atom
b. Otherwise, the lease electronegative atom is central (except hydrogen)
5. Add unshared pairs of electrons so that each hydrogen atom shares a pair of electrons and each other nonmetal is surrounded by eight electrons
6. Count the electrons in the structure to be sure that the number of valence electron used equals the number available.
· EX: CH3I, NH3, H2S, H2O, CH4
Multiple Covalent Bonds: See Table 6-2
· Double and triple bonds are called ______ bonds.
o ______ bonds are covalent bonds produced by the sharing of 2 pairs of electron between 2 atoms.
§ Higher bond energies and shorter than single bonds
§ EX:
o ______ bonds are covalent bonds produced by the sharing of 3 pairs of electrons between 2 atoms.
§ Higher bond energies (Stronger) and shorter than single or double bonds.
§ EX:
Rules:
1. Determine the type & number of atoms in the molecule
2. Write the electron-dot notation for each type of atom in the molecule
3. Determine the total number of valence electrons in the atoms to be combined
4. Arrange the atoms to form a skeleton structure for the molecule, and connect the atoms by electron-pair bonds
a. If carbon is present, then it will be the central atom
b. Otherwise, the lease electronegative atom is central (except hydrogen)
5. Add unshared pairs of electrons so that each hydrogen atom shares a pair of electrons and each other nonmetal is surrounded by eight electrons
6. Count the electrons in the structure to be sure that the number of valence electron used equals the number available.
7. If too many electrons have been used, subtract one or more lone pairs until the total number of valence electrons is correct. Then move one or more lone electron pairs to existing bonds between non-hydrogen atoms until the outer shells of all atoms are completely filled.
EX: See Octet Rule/Lewis Structures In Class Practice WS
Resonance Structures:
· ______ occurs when some molecules and ions cannot be represented correctly by a single Lewis structure.
o EX: See Resonance In Class Practice WS
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