Chemical bonding Chapters 7 and 8. Valence Electrons Elements with similar chemical behavior have...
Preview:
Citation preview
- Slide 1
- Chemical bonding Chapters 7 and 8
- Slide 2
- Valence Electrons Elements with similar chemical behavior have
the same number of valence electrons. For the representative
elements (1A, 2A, 3A, 4A, 5A, 6A, 7A, 8A) the group number
corresponds to the number of valence electron in each group (with
the exception of He) When examining electron configurations, the
electrons that are present in the highest principle energy level
represent the valence electrons of those atoms. Br: [Ar]4s 2 3d 10
4p 5 Bromine has 7 valence electrons
- Slide 3
- Valence Electrons and Electron Dot Structures Valence electrons
are the electrons that participate in chemical bonds Electron dot
structures consist of the atom symbol and its valence electrons
represented as dots. Br: [Ar]4s 2 3d 10 4p 5
- Slide 4
- The Octet Rule - Metals Metals tend to lose electrons to gain
stability. When they lose electrons they attain a stable electron
configuration where the next lowest-energy level has a full
octet.
- Slide 5
- The Octet Rule Non-metals Non-metals tend to gain electrons to
obtain a full octet in their highest occupied p sublevel
- Slide 6
- Formation of Ionic Compounds Cations and anions combine to form
ionic compounds + + NaCl
- Slide 7
- The Formation of Calcium Chloride CaCl 2
- Slide 8
- Properties of Ionic Compounds The chemical formula for an ionic
compound is called a formula unit which represents the lowest who
number ration of atoms in that compound.( ex. NaCl) Most ionic
compounds are crystalline solids at room temperature Ionic
compounds generally have very high melting points Ionic compounds
can conduct electricity when molten or dissolved in water
Coordination Number = The number of ions of opposite charge
surrounding the ion in a crystal.
- Slide 9
- Metallic Bonding Positive metal ions floating in a sea of
electrons. Metals are excellent conductors of electricity Metals
can be easily deformed (They are malleable and ductile) Know that
metals are arranged in crystalline structures, but do not worry
about the arrangement of these structures: face-centered,
body-centered, hexagonal.
- Slide 10
- Alloys Alloys are mixtures of metals Properties of alloys are
usually superior to those of their component elements.
Substitutional AlloyInterstitial Alloy
- Slide 11
- Covalent Bonding Covalent bonds occur between two or more
non-metals Unlike ionic bonds where electrons are transferred from
one atom to another, electrons are shared between atoms in a
covalent bond. Atoms joined together by covalent bonds are called
molecules A compound composed of molecules is called a molecular
compound
- Slide 12
- Molecular and Structural Formulas A molecular formula indicates
the types and numbers of each atom in a molecule The structural
formula indicate the arrangement of the atoms in the molecule
H2OH2O
- Slide 13
- Covalent Bonds and the Octet Rule Atoms share electrons in a
covalent bond so that each atom has enough electrons to satisfy the
octet rule
- Slide 14
- Varieties of Covalent Bonds Single bonds (sigma bonds) en One
pair of electrons is shared between two atoms Lone pair
- Slide 15
- Varieties of Covalent Bonds Double Bonds (1sigma bond, 1 pi
bond) Atoms share two pairs of electrons Triple Bonds (1sigma bond,
2 pi bonds) Atoms share three pairs of electrons
- Slide 16
- Coordinate Covalent Bonds A covalent bond in which one atom
contributes both bonding electrons.
- Slide 17
- Resonance Structures Def: A condition when more than one valid
Lewis structure can be written for a molecule or ion.
- Slide 18
- Exceptions to the Octet Rule Too few electrons surrounding the
central atom (ex: BH 3 ) Boron will not have a full octet, only 6
electrons. It can only achieve a full octet when another atom
shares an entire pair of electrons with it (Coordinate covalent
bonding) Too many electrons surrounding the central atom (ex: PCl 5
) An odd number of electrons
- Slide 19
- How to Draw a Lewis Structure for Molecules Predict the
location of atoms 1. If there are more than two atoms, place the
least electronegative atom in the center and surround it by the
remaining atoms. 2. Hydrogen is always terminal (outside) because
it can only make one bond Determine the total number of electrons
if each atom had a full set of valence electrons (2 for H, 8 for
all others) Add up the number of valence electron that you have to
work with Subtract total valence electrons from total electrons and
divide by two. This is the number of bonding pairs that are needed
to put together the molecule. Connect the atoms with the number of
bonds that you calculated above Add lone pairs where needed so that
each atom has a full octet (except for hydrogen which can only have
two electrons) MoleculeTotal Electrons Valence ElectronsBonding
Pairs HCN
- Slide 20
- Polyatomic Ions Polyatomic ions are a cluster of non-metals
that carry a charge. To draw the structure of a polyatomic ion,
follow the procedure for drawing ordinary molecules but add or
subtract the number of electrons gained or lost to the total number
of valence electrons in your structure as indicated by the charge
on the ion. MoleculeTotal Electrons Valence ElectronsBonding Pairs
IO 3 -
- Slide 21
- Molecular Shape (VSEPR) Valence Shell Electron Pair Repulsion
minimizes the repulsion of shared and unshared pairs of electrons
around the central atom. The shape of a molecule determines many of
its physical and chemical properties. The VSEPR is based on the
arrangement of bonding and lone electrons around a central atom to
minimize repulsion. The repulsion of electrons creates a specific
bond angle between a central atom and two terminal atoms. Lone
pairs of electrons occupy more space than bonding pairs of
electrons
- Slide 22
- Molecular Geometry or 2
- Slide 23
- Electronegativity and Polarity Recall: Electronegativity is the
ability of an atom to attract an electron.
- Slide 24
- Chemical bonding is like Tug-o-War Non-polar Covalent0-0.4
Polar Covalent0.5-2.0 Ionic>2.0 Electronegativity Bond Type
Difference
- Slide 25
- Molecular Polarity Molecules are either polar or non-polar Both
polar and non-polar molecules may contain polar bonds. What
determines whether a molecule is polar or non-polar is the symmetry
of the molecule PolarBonds Present Symmetr y Polar/ Non- Polar
Examples No Non-PolarNO 2 NoYesNon-polarSiH 4 YesNoPolarNH 3 Yes
Non-polarCO 2 VSEPR shapes that can demonstrate symmetry are:
Linear Trigonal PlanarTetrahedral