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Octet Rule
Octet Rule: Atoms will gain, lose, or share valence electrons in order to obtain a stable outer shell electron configuration of 8 valence electrons. (H and He only need 2)
Lewis Electron Dot Structures
Lewis Structures – use dots to represent valence electrons
3 6 4 2 7 1 5 8
X
Chemical Bonds
1. Chemical Bonds: Attractive forces that hold atoms together due to the mutual attraction between the nuclei and their valence electrons.
2. Three types of Chemical Bonds Ionic Covalent (Polar & Nonpolar) Metallic
Metallic Bonds
Metallic bonds: result from the delocalized sharing of valence electrons between metal atoms.
Example: Aluminum, Copper, Iron
Electronegativity
Electronegativity – the ability of an atom in a molecule to attract electrons to itself
Metals = low values(Ionization energy too)
Nonmetals = high values(Ionization energy too)
Note Trend:Across increaseDown decrease
Types of Bonds
Type Ionic Polar
CovalentNonpolar Covalent
Electronegativity Difference…
>1.7(equal to or more
than 1.7)
1.7>x>0(less than 1.7 but more than zero)
= zero
Valence Electrons are…
Transferred Shared unequally
Shared Equally
How to Recognize…
Metal & Nonmetal
2 Different Nonmetals
2 of the same Nonmetals
Chemical Formula for one example…
NaCl H2O H2
Ionic Bonding
1. Metals lose electrons and form cations . Na +
2. Nonmetals gain electrons and form anions. Cl –
3. Ionic Bonds form due to the attractions between the metal ions and nonmetal ions.
Lattice Energy
1. Lattice Energy is the energy needed to separate an ionic lattice into gaseous ions.
2. Lattice Energy increases with: Increasing charge on the ions LE stronger in MgO than NaCl Decreasing distance between the ions (LE is stronger between smaller radii ions) LE stronger in LiF than in CsBr3. The greater the LE, the higher the melting point.
Covalent Bonds vs Ionic Bonds
Covalent Bonds: form when valence electrons are shared between atoms of 2 nonmetals
Ionic Bonds: form when valence electrons are transferred from a metal atom to a nonmetal atom
Covalent Bonds1. Single Bond – sharing of 1 electron pair
2. Double Bond – sharing of 2 electron pairs
3. Triple Bond – sharing of 3 electron pairs
Bond Length & Strength
Single bonds: Longer Bond Lengths Lowest Bond Energies (weak bonds)Triple bonds: Shorter Bond Lengths Highest Bond Energies (strong bonds)
Bond Polarity
1. Nonpolar Covalent Bond – electrons are shared equally between two atoms
Br2
2. Polar Covalent Bond – one atom exerts a greater attraction for the bonding atoms
H2O
3. The greater the electronegativity difference between the atoms, the more polar the bond.
Rules for Drawing Lewis Structures for Molecules & Polyatomic Ions
1. Find the number of valence electrons in each atom and add them up.
(Note: - ions have gained e-, + ions have lost)2. Draw symbols of the atoms near each other in the
way they will bond. 3. Connect the atoms by single bonds (1 e- pair)4. Complete octets on atoms bonded to the central
atom. (except hydrogen gets 2)5. Place leftover electrons on the central atom.6. If there aren’t enough electrons to give the central
atom an octet, try double or triple bonds.