Transcript Unit 9 Notes - My Teacher Pages

Unit 9 Bonding
Test Wed. 2/17
Why do atoms form bonds?
• to have the most stable electron configuration
for its electrons
• to achieve a lower, more stable, energy state
How atoms bond with each other depends on:
e
e
e
e
Electronegativity
Ionization Energy
# Valence Electrons
Valence electrons
• To find the of valence electrons in an atom of
a representative element, look at the last digit
of its group number.
Electron dot structure
• Also called “Lewis
valence electron dot
structure”
Octet rule
• In forming compounds, atoms tend to achieve the
electron configuration of a noble gas
• Fill up their highest energy level with 8 electrons OR
• Empty their highest energy level to Zero electrons
cation
I’m “paws-itive”
• A positively charged
ion, or cation, is
produced when an
atom loses one or more
valence electrons.
Formation of a cation
Watch This
anion – formed when an atom
gains valence electrons
• Nonmetals attain noble-gas configurations by
gaining electrons.
“losers on the left”
GAIN
VALENCE
ELECTRONS
LOSE VALENCE ELECTRONS
PRACTICE
How many valence electrons?
• Potassium
• Carbon
• Magnesium
• Oxygen
Ionic compound
• Composed of cations and anions
Ionic compounds are electrically neutral.
IONIC BOND
an electrostatic* force that holds ions together in ionic compounds
*Electrostatic refers to the attraction between opposite charges
Ionic bonding video 1
Ionic bonding video 2
Chemical formula
• Shows the number of each element in the
smallest representative unit of a substance.
Writing Lewis Dot Structures - Ionic
• Metals tend to lose e- while nonmetals tend to gain
electrons
hyperphysics.phy-astr.gsu.edu
Writing Lewis Dot Structures – Ionic Bonds
• Metals tend to lose e- while nonmetals tend to gain
electrons
chemistry58.wikispaces.com
Ionic bonds
Writing Lewis Dot Structures –
Ionic Bonds
1.
2.
3.
4.
5.
Write the Lewis dot structure for each type of atom involved in the
compound.
Determine which atom will lose electrons (metal) and which atom will
gain electrons (nonmetal).
Draw arrows to show the electrons moving from the metal to the
nonmetal.
If an octet is not filled for the nonmetal or if you don’t use up all of the
metal’s valence electrons, you will need add more nonmetal or metal
atoms. Draw as many atoms of the metal as necessary to fulfill the octet
for the nonmetal and use all of the valence electrons from the metal.
Consolidate your diagram.
–
–
Draw the metal on the left with its charge in the upper right corner. (If more than one
of these was needed, write a coefficient in front of the metal.)
Draw the nonmetal with its octet. Enclose it in brackets. Include the charge outside of
the brackets in the upper right corner. (If more than one of these was needed, write a
coefficient in front of the nonmetal.)
Properties of ionic compounds
(all related to the strong attraction between
the + and – charges)
• hard, crystalline solids at room temperature
• high melting points (and boiling points)
• good conductors – in aqueous solutions
(dissolved in water) and when molten
(melted)
not
crystalline
Metallic bonding
http://www.bbc.co.uk/schools/gcsebit
esize
Watch This
To describe the nature of
metallic bonding,
consider the valence
electrons of atoms in a
pure metal to behave as
a 'sea' of delocalized
electrons.
Metallic bond
• the forces of attraction between free-floating
(delocalized) electrons and positively charged
metal ions.
• Watch This
http://www.launc.tased.edu.au/online/sciences/PhysSci/pschem/metals/Met
als.htm
• Ductility – property of a metal that enables it
to be drawn into a wire
• Malleability- means that a metal can be
hammered into a sheet
Electrical conductivity
• To conduct an electric
current through the flow of
electrons
Thermal conductivity
• Transfer heat
video1
Video 2
alloy
• A mixture of 2 or more
metals
(KP p. 224) Alloys are important because their properties are often
superior to those of their component elements.
Really, we don’t hate you.
Covalent Bond
• formed when atoms are
held together by sharing
electrons
• Molecule - formed when
two or more atoms bond
covalently.
• A molecule is to a
covalent bond as a
formula unit is to an ionic
bond.
33
Number of bonds
• single covalent bond when 1 pair of electrons
is shared between 2
atoms
• double covalent bond –
when 2 atoms share 2
pairs of valence
electrons; ex. O2
• Triple covalent bond –
when 2 atoms share 3
pairs of valence
electrons; ex. N2
34
(Review) Diatomic Molecules
• HOFBrINCl
Share electrons when they bond together
35
Polyatomic Ions
• covalently bonded
group of atoms, with a
+ or - charge
• Watch this
36
Bond type video
equal sharing of electrons
between atoms
unequal sharing of electrons
between atoms
Transfer of electrons between
atoms
occurs between the two
atoms in a diatomic molecule
(H-H) and between C and H
atoms (CH4)
occurs between other
combinations of nm-nm or
nm-metalloid
occurs between m-nm
Types of Bonds:
38
Writing Lewis Dot Structures - Covalent
Bonds
Bonding e- Pairs
Lone Pairs
(nonbonding electrons)
How to draw Lewis dot structures for
covalent molecules.
1.
2.
Count the total number of valence electrons.
Predict the location of the atoms:
a) Hydrogen is NEVER the central atom.
b) If carbon is present, it is ALWAYS the central atom.
c) If there is only 1 atom of an element, it is the central atom.
d) The least electronegative atom is generally the central atom.
3. Place one electron PAIR between the central atom and each ligand (side
atom) to “hook” the atoms together.
4. Dot the remaining electrons in pairs around the compound to complete
the octet. Start with the ligands.
5. Check that each atom has an octet. (H only needs a pair, not an octet.)
Watch This
40
Lewis Structures for Molecules
• Draw the Lewis dot structure for these
molecules:
– Hydrogen + Bromine (HBr)
– Carbon + Chlorine (CCl4)
41
Why are molecular shapes
important?
• The shape of a
molecule plays a
very important role
in determining its
properties.
• Properties such as smell, taste, and
proper targeting (of drugs) are all the
result of molecular shape.
valence shell electron pair repulsion
VSEPR Theory
also called electron geometry
• Electron groups around the central atom will
be most stable when they are as far apart as
possible.
TO DETERMINE
VSEPR SHAPE (electron geometry)
1) Draw the Lewis dot structure for the molecule
2) Identify the central atom
3) Count the number of electron groups around the
central atom.
-an electron group can be a lone pair or a bond
(single, double, or triple)
4) Look up the VSEPR shape on the chart.
**shapes with no lone pairs are symmetrical
**shapes with lone pairs are assymmetrical
44
Two Electron Groups: Linear Electron
Geometry
• When there are two electron groups around the
central atom, they will occupy positions on opposite
sides of the central atom.
• This results in the electron groups taking a linear
shape.
Linear Geometry
Three Electron Groups:
Trigonal Planar Electron Geometry
• When there are three electron groups around the
central atom, they will occupy positions in the shape
of a triangle around the central atom.
• This results in the electron groups taking a trigonal
planar shape.
Trigonal Planar Geometry
Four Electron Groups: Tetrahedral
Electron Geometry
• When there are four electron groups around the
central atom, they will occupy positions in the shape
of a tetrahedron around the central atom.
• This results in the electron groups taking a
tetrahedral shape.
Tetrahedral Geometry
Molecular Geometry
• The actual geometry of the molecule may be
different from the VSEPR shape.
• Lone pairs repel bonded atoms which distorts the
expected shape.
Bond Angle Distortion from Lone
Pairs
Electron Geometry:
Molecular Geometry:
Tetrahedral
Tetrahedral
Tetrahedral
Trigonal Pyramidal
Tetrahedral
Bent
Watch This
Practice:
• Determine the shape.
1. NF3
2. SiCl4
3. H2O
54
Water is a POLAR
molecule
The more electronegative atom will have a slight
negative charge, the area around the least
electronegative atom will have a slight positive
charge.
55
Symmetric (no lone pairs around the central atom)
molecules tend to be nonpolar.
Asymmetric (at least one lone pair around the central
atom) molecules with polar bonds are polar.
56
Video
CHARACTERISTICS OF IONIC AND MOLECULAR COMPOUNDS
CHARACTERISTIC
Representative unit
Bond Formation
Type of elements
Physical state
Melting point
Solubility in water
Electrical conductivity of
aqueous solution
IONIC COMPOUND
MOLECULAR COMPOUND