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Chemistry 2--Chap 6 Review Sheet
Chap 6 Covalent Compounds:
Section 1: Covalent Bonds
Sharing electrons = covalent bonds.
Molecular orbitals = space around 2 atoms that share electrons, where the e-s are (90% of the
time).
*** Diatomic elements: H2, O2, N2, and halogens (F2, Cl2, Br2, I2, At2).
At BrINClHOF or H7
Bond formation: Energy is released when a bond forms (exothermic), the bonded molecule is
more stable = less energy (like the meter stick on the floor).
Energy must be put in to break a bond.
Bond length = distance (average) from one nucleus to the other that gives lowest potential energy:
BALANCE between repulsive/attractive forces of all e-s and nuclei (+).
Bonds vibrate and rotate, they are flexible.
Bond Energy: Bonds have different strengths. Shorter bond length = stronger bond (due to greater
nuclear attraction/greater pot. energy drop).
Bond strength: (weakest) single < double < triple (strongest)
Electronegativity: Attraction of a nucleus for the electrons of another atom in a bond.
In a bond atoms can share the electrons:
1) sharing equally = non-polar bond
2) sharing unequally = polar bond
3) not share, complete loss and gain of electron = ionic bond
Be able to: Calculate (quantitative) how electrons are shared using Electronegativity.
ELECTRONEGATIVITY DIFFERENCE = ∆EN.
Spectrum of ∆ EN: page 195
0
non-polar
(pure covalent)
0.5 0.6
polar covalent
Use chart on page 194.
2.1 2.2
ionic
3.3
POLAR BONDS
Every POLAR BOND: has a Dipole : one end of the bond is more negative (higher EN) and the
other end is positive (lower EN).
Use lower case delta (∂) and the sign
 ∂- for the partial negative end
 ∂+ for the partial positive end
Example: Hydrogen bonded to Oxygen
EN = 2.1
EN = 3.4
+------->
H ----- O
∂+
∂-
 and/or an arrow that points to the negative end.
Physical Properties and Polarity:
 For Covalent compounds (non-polar and polar), molecules with more polarity are more
attracted to each other and thus have higher melting and boiling points.
 Solubility: LIKE DISSOLVES LIKE
Chemistry 2--Chap 6 Review Sheet
Polar dissolves polar and ionic (water and salts, water and sugar)
Non-polar dissolves non-polar (Oil dissolves fats)
Oil and water don’t mix!
 Ionic compounds have very strong attraction between the ions, so they have very high melting
and boiling points.
 Metals (elements) have a different kind of attraction (called “metallic bonding”) because of the
loose valence electrons. This gives metals their distinctive properties.
Section 2:
 Lewis/e- Dot Structures: Drawings showing the electrons around each atom as dots. Use 4
positions around the atom: top, bottom, right, left. Electrons go in pairs if possible.
Includes single atoms, compounds, multiple bonds, simple ions and polyatomic ions.
 Naming Covalent compounds: Binary covalent compounds: 2 non metals, use prefixes to tell
number of atoms. {This is different from ionic compounds, pay attention to the differences}
Prefixes: mono, di, tri, tetra, penta, hexa, hepta, octa, nona, deca,…
The second element’s name changes to an –ide ending.
Don’t use mono on the first element.
 Be able to name and write formulas for: Ionic compounds (including polyatomic ions),
Covalent compounds, and acids when mixed up. See Naming Summary handout.
Section 3: VSEPR Theory, Shapes and Polarity
VSEPR= Valence Shell Electron Pair Repulsion: electron pairs in orbitals repel each
other (like charges repel), so they distribute themselves evenly in space. The most common number
of pairs of valence electrons is 4 (remember the octet rule).
SHAPES:
The shapes in bonded atoms are different from the shape in single atoms (s, p, d, f).
The shape in bonded atoms comes from connecting the atoms with lines.
 2 atoms = linear
 Four (4) pairs of electrons on a central atom:
Tetrahedral = 4 bonded atoms, bond angle of 109.5o
Trigonal pyramid = 3 bonded atoms (1 lone pair)
Bent = 2 bonded atoms (2 l.p.)
 Three (3) pairs of electrons on central atom and 3 bonded atoms = Trigonal Planar, bond
angle of 120o
Bent = 2 bonded atoms (1 l.p.)
 Four (4) pairs of electrons, 2 double bonds, 2 bonded atoms = Linear, bond angle of 180o
Polarity of Molecules: to figure it out use the questions:
1.
Are the bonds polar?
If NO, molecule is Non-polar.
If YES, check the shape.
2.
Does the shape have a negative end and a positive end?
If NO, the molecule is Non-polar.
If Yes, the molecule is Polar.
(symmetric)
(asymmetric)