Unit A Outcome 2 Flashcards
Molecular (covalent) Bonding
-Occurs between non-metal atoms
If the atoms are the same the result is a molecular element.
Eg. N2(g), O2(g), P4(s)
If the atoms are different, the result is a molecular compound.
E.g. CO2(g), H2O(l), N2O(g)
What are the four types of formulas?
Molecular formula – shows all atoms in the compound, often in the
order that they are bonded
Ex. CO2, CH3OH
Lewis formula – uses Lewis symbols to show bonding
Structural formula – shows which atoms are bonded using lines
between atom symbols
Stereochemical formula – represents the 3D shape of the compound
What do the lines mean in a stereochemical formula?
straight black line: in the plane
dotted line: goes backward
Black triangle line: Forward
What formula is preferred with molecular covalent bonds
For molecular (covalent) compounds it is often more appropriate to use a
structural formula to represent the bonding that takes place between two atoms
Bonding Capacity
maximum number of bonds that an atom can make
Equals the number of bonding electrons that an atom has
How do you create a Lewis diagram for molecular compounds
1.Count total valence e- in the compound by adding the valence e- for
each atom.
Eg. SO2 –
S has 6, O has (6 x 2 atoms) 12
6 + 12 = 18 valence electrons
2.Arrange peripheral atoms around central atom
3.Central atom is one with highest bonding capacity
4.Place one pair of electrons between each peripheral atom and the
central atom
5.Place more pairs of electrons on all the peripheral atoms to complete
their octets.
6.Place any remaining valence electrons on the central atom as lone pairs
How do you create a structural diagram
First start with the Lewis Diagram
Replace every pair of shared electrons with a single line
Don’t show lone pairs
Examples: Draw the Lewis and Structural Diagrams for the following
compounds
Vseper theory
Valence-shell-electron-pair-repulsion theory, or VSEPR, allows us to predict the
stereochemistry of a molecular compound based on its Lewis structure.
What are the rules of Vseper theory
Pairs of electron stay as far away from each other as
possible
Only valence electrons on the central atom are important
for molecular shape
Valence electrons are paired.
Bonded electron pairs and lone pairs are equal
Electron pairs repel each other
Molecular Shape is determined when e- pairs are a max
distance apart
What are the five possible geometric shapes in Vseper
Linear
Bent (v-shaped)
Tetrahedral
Trigonal
Pyramidal
Trigonal Planar
Linear Molecule
A linear molecule involves a central atom bonded to two other atoms with no lone
pairs OR a molecule composed of only two atoms.
Examples:
CO2 , HCN , HCl
Bent (V-shaped) Molecules
A bent molecule involves a central atom bonded to two other atoms and has either
one or two lone pairs
Examples:
H2O , HNO
Tetrahedral Molecules
A tetrahedral molecule involves a central atom bonded to four other atoms and
has no lone pairs
Example:
CH4
Trigonal Planar Molecules
A trigonal planar molecule involves a central atom bonded to three other atoms
and has zero lone pairs.
Example:
CH2O
Pyramidal Molecules
A pyramidal molecule involves a central atom bonded to three other atoms with
one lone pair
Example:
NH3
Polar molecule
A polar molecule is one in which the negative charge (electrons) is not distributed
symmetrically among the atoms making up the molecule. Thus, it will have partial positive
and negative charges on opposite sides of the molecule.
If two bonded atoms have different electronegativities, they will
have unequal sharing of the shared pair of electrons
Polar covalent bond
Covalent bond in which the two bonded atoms have a different
electronegativity
Atoms un-equally share electrons
Non-polar covalent bond
Non Polar covalent bond
Covalent bond in which the two bonded atoms have the same
electronegativity
Atoms equally share electrons
Bond dipoles
We represent a polar bond with an arrow in the direction of the
electron pull and the partial charge symbols
Polar Molecule
A molecule in which the –ive charge is not distributed
symmetrically among the molecule
Non polar molecule
A molecule in which the –ive charge is distributed
symmetrically among the molecule
Intermolecular force
the breakage of bonds between the molecules
Intramolecular force
the breakage of bonds within molecules
What are the three types of intermolecular forces
LONDON FORCE
DIPOLE-DIPOLE FORCE
Hydrogen Bonding
London Force
While non-polar molecules are thought to have an overall charge of zero,
electron movement within a given molecule may still produce a
momentary dipole; this results in what is known as London force.
more molecules= greater London force
-high e-
Dipole Dipole
Attraction between the dipoles of polar molecules is referred to as
dipole-dipole force.
-Weakest force
How to determine solubility with polar and non polar molecules
like dissolves like
Polar molecules dissolve in polar molecules
Nonpolar molecules dissolve in nonpolar molecules
Hydrogen Bond
Certain compounds have higher boiling points than we might expect based on their size and polarity.
other than dipole-dipole and London forces must be acting between
the molecules of these compounds. This phenomenon is the result of hydrogen bonding.
-Strong4est force
-only with N,O,F
What is a rule about IM forces and Boiling points
The greater the intermolecular forces (I.M.) that hold together molecules
in a given substance, the higher the boiling point of that substance…
