BONDING
Part 1- Internal Bonds
I. Why do Atoms Want to Combine Chemically? (Read 15.1)
A. Stable Electron arrangements
Most stable elements: noble gases
Why? have outermost s and p sublevels filled with electrons
Outer shell configuration of noble gases: ns2np6 (n=energy level)
Example: Ar 1s22s22p63s23p6
What do other elements want? to be stable and have electron
configuration similar to noble gases
How do they do this? bonding
* ALL ELEMENTS WANT TO BE stable
B. Lewis Dot Structures
. shows valence electrons as dots
. inner electrons and the atomic nucleus are represented by the symbol for the
element
Atom or Ion Electron configuration Lewis Dot Structures
Li (neutral atom) 1s22s1
Li .
F 1s22s22p5
F
Ar 1s22s22p63s23p6
Ar
Li+ 1s2
Li+
F- 1s22s22p6
F
II. Types of Internal Bonding
A. Metallic Bonding
1. Elements Involved
Which element do it? elements to the left of the stair step line
Common examples: Pb , Al
Properties of these elements:
Low ionization energy (easy to remove electrons)
Low electronegativity (LOSERS)
2. Electron Action
What do they want to do to become stable? LOSE electrons
Example: Al
Al
1s22s22p63s23p1
+13
Al To become stable:
1) will Al gain 5 electrons? NO
2) will Al LOSE 3 electrons? YES
What do they do?
Al Al Promote
electrons to
higher energy levels
3. Resulting Particles and structures
Al -------> Al3+ +
3e-
neutral atom cation floating electrons
Al Al
Al Al
Structure: Cations surrounded by electrons
What is the bond? the bond is the attraction of electron cloud to cations
Strength of the bond: medium
4. General Properties of Metals
1) malleable
2) ductile
3) good conductors of electricity
4) high thermal conductivity
B. Nonpolar Covalent Bonding (Read 16.1)
1. Elements involved
Which elements do it? nonmetals; elements to the right of the stair step
line and H
Common examples: H , O , N , X (halogens)
Properties of these elements:
High ionization energy
High electronegativity
2. Electron Action
What do they want to do to become stable? SHARE
Example:
H 1s1 H.
What do they do?
H. .H
H. .H
H. + .H -------> H H
Note: the nuclei are identical and attract the pair of electrons with equal
strength. The pair of electrons is shared equally between the atoms.
This is a nonpolar, covalent bond.
(equal) (shared)
Can be shown: H H or H - H
Example: Halogens
General Lewis Dot structure:
X X = halogen
this electron is in a p orbital
F + F ----->
Diatomic fluorine is represented:
F2 or F F or F - F
What other elements are formed in this same way?
Sigma Bonds
H2 F2
H - H F - F
H H F F
When electrons are shared in this location - along the internuclear axis -
the bond is a sigma bond.
The bond in H2, F2, Cl2, Br2, and I2 is also called a single bond.
Single covalent bond - single pair of electrons is shared
Pi Bonds
Example: two oxygen atoms
double covalent bond - two pairs of electrons are shared
pi bond - the bonding electrons are most likely found above and below the
internuclear axis
A pi bond is weaker than a sigma bond.
double covalent bond - consists of one sigma bond and one pi bond
What other element forms a diatomic molecule in this way?
Example: two nitrogen atoms
triple covalent bond - three pairs of electrons are shared
triple covalent bond - consists of one sigma bond and two pi bonds
What other element forms a diatomic molecule this way?
C. Polar Covalent Bonds
1. Elements involved
Which elements do it? nonmetals
Common example: H and Cl, N and H, H and O
Properties of these elements:
High electronegativity
High ionization energy
What do they want to do to become stable? SHARE
2. Partial Charges
Example: H and Cl
H Cl
H Cl a single sigma bond is formed
BUT, NOT a nonpolar covalent
bond because they do not share
electrons equally
The atom with the higher electronegativity pulls the shared electron pair closer
to its nucleus . This atom obtains a partial negative charge, .
The other atom, which has the lower electronegativity charge, attains a partial
positive charge, .
This type is bonding, with unequal sharing of electrons, is called
polar covalent bonding
(unequal) (shared)
Example: N and H
3. Resulting Structures and Molecular Geometry: VSEPR theory
a. Using the Octet Rule to write Lewis electron dot structures
Steps for writing dot structures:
1. Determine the number of valence electrons from all the atoms. For a
polyatomic anion, add one electron for each unit of negative charge. For a
cation, subtract one electron for each unit of positive charge.
2. Write the skeleton structure.
3. Place one pair of electrons between each set of bonded atoms.
4. Subtract the number of electrons used so far from the total available.
5. Complete the octets of the atoms attached to the central atom by adding pairs
of electrons. (Hydrogen is an exception - it will have only two electrons.)
6. Count the electrons in the structure and subtract from the total to be used.
Place the remaining electrons on the central atom.
7. If the central atom has an octet, the electron dot structure is complete. If
the central atom does not have an octet of electrons, form double bonds and
triple bonds as necessary.
b. Using VSEPR theory to predict the shape of molecules
VSEPR = valence shell electron pair repulsion
What do the molecules look like?
Example: diatomic molecules
Linear
Trigonal Planar
Tetrahedral
Trigonal Pyramidal
Bent
c. Resonance Structures
4. General Properties of Molecular Compounds
1. can be solid, liquid, or gas
2. low melting point
3. poor conductors of heat
D. Ionic Bonding (Read 15.2)
1. Elements involved
Which elements do it? metals and nonmetals
Common examples: Na and Cl, Ba and F, K and S
Properties of the elements:
One is a GRABBER One is a LOSER
High ionization energy Low ionization energy
High electronegativity Low electronegativity
What do they want to do to become stable?
One wants to grab electrons One wants to lose electrons
2. Electron action
Example: Na and Cl
Na Cl ----> NaCl
Ionic Bond - attraction between positively charged ions and negatively charged
ion
3. Resulting particles and structures
When many ions of Na and Cl attract each other, the final structure looks like
this:
No molecules are present, only a continuous lattice of crystal of + and - ions.
Example: Ba and F
Example: K and S
4. General Properties
1. crystalline solids at room temperature
2. high melting points
3. form conducting liquids when melted or dissolved in water
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