Transcript Chapter 8 - Covalent Compounds

Covalent compounds
• A covalent compound consists of two
or more nonmetals.
• They are able to bond together by
sharing their valence electrons.
Covalent compounds
• Atoms will share 1, 2, or 3 pairs of
electrons so that each valence level
has a stable octet.
• This sharing of electrons is the bond
that keeps the atoms together.
Covalent compounds
• Single covalent bond – Atoms share 1
pair of electrons.
• Double covalent bond – Atoms share
2 pairs of electrons.
• Triple covalent bond – Atoms share 3
pairs of electrons.
Covalent compounds
• We can determine how many pairs of
electrons are shared by drawing an
Electron-Dot Diagram.
Covalent compounds
• Steps for drawing Electron-Dot
Diagrams;
• 1.) Add up the number of valence electrons that
each atom brings to the compound.
• 2.) Arrange the atoms in the compound next to
each other. If there are more than two atoms in
the compound, arrange them symetrically with
the atom that was listed first as the central atom.
• 3.) Place 1 pair of electrons between each atom
that will be bonded together.
Covalent compounds
• Steps for drawing Electron-Dot
Diagrams (cont.);
• 4.) Use the remaining electrons to satify the octet
rule for each element in the compound.
• 5.) If there are not enough electrons, place
another pair of electrons between 2 atoms.
• 6.) If there are extra electrons, place them on the
central atom, even if it already has 8 electrons.
Covalent compounds
• Electron-Dot Diagrams;
• Draw the EDD for chlorine gas (Cl2).
• Each atom brings 7 valence electrons
for a total of 14 electrons.
• Bond the chorine atoms with a single
pair of electrons. Now there are 12
electrons left.
Cl:Cl
Covalent compounds
• Electron-Dot Diagrams;
• Place 6 more electrons around each
chlorine atom. The Octet Rule is
satisfied for both atoms.
Cl:Cl
Covalent compounds
• Electron-Dot Diagrams;
• Draw the EDD for bromine (Br2).
Covalent compounds
• Electron-Dot Diagrams;
• Draw the EDD for carbon
tetrachlorde (CCl4).
Covalent compounds
• Electron-Dot Diagrams;
• Draw the EDD for Oxygen gas (O2).
Covalent compounds
• Electron-Dot Diagrams;
• Draw the EDD for Nitrogen gas
(N2).
Covalent compounds
• Electron-Dot Diagrams;
• Draw the EDD for Carbon
monoxide (CO).
Covalent compounds
• Electron-Dot Diagrams;
• Draw the EDD for carbon dioxide
(CO2).
Covalent compounds
• Exceptions in drawing Electron-Dot
Diagrams;
• Just like everything else in
Chemistry, there are exceptions to
the Octet Rule.
• Hydrogen – Stable with only 2 valence
electrons.
• Boron – Stable with 6 valence electrons.
• Sulfur and Phosphorous – Stable with 8,
10, or 12 valence electrons.
Covalent compounds
• Exceptions in drawing Electron-Dot
Diagrams;
• Draw the EDD of Hydrogen
Chloride (HCl).
Covalent compounds
• Exceptions in drawing Electron-Dot
Diagrams;
• Draw the EDD of boron trifluoride
(BF3).
Covalent compounds
• Exceptions in drawing Electron-Dot
Diagrams;
• Draw the EDD of phosphorus
pentachloride (PCl5).
Covalent compounds
• Draw the electron dot diagram for
the ammonium ion.
Covalent compounds
• Resonant Structures
o
o
Resonant structures are multiple ways of drawing
an EDD for a molecule.
The nitrate ion, NO3-1, has three different ways to
draw its dot diagram;
Covalent compounds
• Resonant Structures
o
Which molecule has resosnant structures, SO3 or
SO3-2?
Covalent compounds
• Coodinate Covalent Bonds
o
A coordinate covalent bond forms when one
atom donates both electrons that are used to
form a covalent bond.
Covalent Compounds
• Naming Covalent Compounds
– Prefixes have to be used since different
compounds can have different ratios of the same
elements.
mono = 1, di = 2, tri = 3, tetra = 4, penta = 5,
hexa
= 6, hepta = 7, octa = 8, nona = 9, and
deca =
10
Covalent Compounds
• Naming Covalent Compounds
– Use a prefix to indicate the number of atoms of each
element in the covalent compound and add the suffix
‘ide’ to the name of the last element.
• N2O4 = dinitrogen tetroxide
• P2O10 = diphophorous decoxide
• CO2 = carbon dioxide *
• CO = carbon monoxide *
* If there is only one of the first element, don’t use
a prefix. It is implied that there is only 1 atom in
the compound.
Covalent Compounds
• Naming Covalent Compounds
– Name these covalent compounds;
• H2O
• CCl4
• CS2
• CCl4
• S2O6
Covalent Compounds
• Naming Covalent Compounds
– There is a special type of covalent compounds called
acids.
• An acid will always contain hydrogen.
• The hydrogen will be listed first.
• Acids have a different naming system.
Covalent Compounds
• Naming Covalent Compounds
– Naming Acids that do not contain oxygen;
• Use the prefix ‘hydro’ on the name of the second element
with the suffix ‘ic’.
– HCl = hydrochloric acid
– HF = hydrofluoric acid
– H2S = hydrosulfic acid
Covalent Compounds
• Naming Covalent Compounds
– Naming Acids that contain oxygen;
• If the anion ends in ‘ate’, then use the suffix ‘ic’ on the name
of the anion.
– H2SO4 = sufuric acid
• If the anion ends in ‘ite’, then use the suffix ‘ous’ on the
name of the anion.
– H2SO3 = sulfurous acid
Covalent Compounds
• Naming Covalent Compounds
– Name these acids;
• HI
• HCl
• H3PO4
• H2C2O4
• HC2H3O2
Covalent Compounds
• VSEPR Theory
– Valence Shell Electron Pair Repulsions
• Bonding electrons and lone pairs of electrons will repel
themselves so that they will separate by the maximum
distance possible.
Covalent Compounds
• VSEPR Theory
– Valence Shell Electron Pair Repulsions
• The shape of a molecule is determined by these
repulsive forces.
Covalent Compounds
• VSEPR Theory
– Valence Shell Electron Pair Repulsions
• Linear Shape
– A molecule consisting of just 2 atoms will always be linear.
– A molecule with 3 atoms can be linear if there are no lone
pairs of electrons on the central atom.
Covalent Compounds
• VSEPR Theory
– Valence Shell Electron Pair Repulsions
• Bent Shape
– A molecule that has 3 atoms but there is a lone pair(s) of
electrons on the central atom.
Covalent Compounds
• VSEPR Theory
– Valence Shell Electron Pair Repulsions
• Trigonal Planar Shape
– A molecule that has 4 atoms with no lone pairs on the central
atom.
Covalent Compounds
• VSEPR Theory
– Valence Shell Electron Pair Repulsions
• Trigonal Pyramidal Shape
– A molecule that has 4 atoms with a lone pair of electrons on
the central atom.
Covalent Compounds
• VSEPR Theory
– Valence Shell Electron Pair Repulsions
• Tetrahedral Shape
– A molecule that has 5 atoms with no lone pairs of electrons on
the central atom.
Covalent Compounds
• VSEPR Theory
– Valence Shell Electron Pair Repulsions
• Trigonal Bipyrimidal Shape
– A molecule that has 5 atoms with no lone pairs of electrons on
the central atom.
Covalent Compounds
• Bond Polarity
o Polar – having two distinct ends.
o Sometimes, there is an unequal sharing of the
electrons that make up a covalent bond. As a
result, the bonding electrons can spend more time
with atom compared to the other one.
Covalent Compounds
• Bond Polarity
o The atom with the higher electronegativity value
will have the bonding electrons most of the time.
o The atom with the higher electronegativity will
have a partial negative charge (δ-).
Covalent Compounds
• Bond Polarity
o The atom with the lower value of electronegativity
will appear to have a positive charge (δ+).
Covalent Compounds
• Bond Polarity
o If two bonding atoms have the same
electronegativity, the bond will not appear to be
polar.
Covalent Compounds
• Bond Polarity
o When determining if a molecule is polar or
nonpolar, you must analyze the entire molecule
and consider its shape.
o CO2 is nonpolar.
δ-
δ+
δ-
O=C=O
Covalent Compounds
• Bond Polarity
o When determining if a molecule is polar or
nonpolar, you must analyze the entire molecule
and consider its shape.
o CCl4 is nonpolar.
Covalent Compounds
• Bond Polarity
o When determining if a molecule is polar or
nonpolar, you must analyze the entire molecule
and consider its shape.
o H2O is polar.
Covalent Compounds
• Bond Polarity
o When determining if a molecule is polar or
nonpolar, you must analyze the entire molecule
and consider its shape.
o HCl is polar.
Covalent Compounds
• Bond Polarity
o When determining if a molecule is polar or
nonpolar, you must analyze the entire molecule
and consider its shape.
o Is NH3 polar or nonpolar?
Covalent Compounds
• Bond Polarity
o Electronegativity Table
Covalent Compounds
• Are the following compounds polar or non
polar?
o PH3:
o SO3:
o H2S:
o I2:
o CS2:
Covalent Compounds
• Intermolecular Forces
– Forces of attraction between 2 or more other
molecules in a substance.
Covalent Compounds
• Intermolecular Forces
– 3 types: London Dispersion Forces (weakest),
Dipole-Dipole, and Hydrogen Bonding (strongest).
Covalent Compounds
• Intermolecular Forces
– London Dispersion Forces: Weak forces of
attractions caused by the attraction between the
protons in one molecules and the electrons in
another molecule.
Covalent Compounds
• Intermolecular Forces
– Dipole - Dipole Forces: Weak forces of attractions
caused by the attraction between the oppositely
charged poles of two or more molecules.
Covalent Compounds
• Intermolecular Forces
– Hydrogen Bonding: Forces of attractions between
a hydrogen atom of one molecule and a fluorine,
oxygen, or nitrogen, of another molecule.
Covalent Compounds
• Intermolecular Forces
– Hydrogen Bonding: Forces of attractions between
a hydrogen atom of one molecule and a fluorine,
oxygen, or nitrogen, of another molecule.