Chemical Bonding
1/7/11 – “C” day
Objective:
Describe the interactions that occur
between atoms when bonding occurs
Do Now:
Do you remember – what is the name
of LiCl or MgBr2?
Chemical Bonding 1/10/11 – “D” day
Objective:
Describe the interactions that occur
between atoms when bonding
occurs
Do Now:
Draw the lewis dot structures to
determine how the following bond:
Li & Cl
Mg & N
What’s due`
• Due by the end of class pages 1-8 of
Naming Compounds Packet
• Due tomorrow before quiz – Review Sheet
Valence Electrons
• Chemical bonds result from the
sharing or transfer of valence
electrons
• Valence electrons are those in the
outermost energy level (think Bohr
model)
• http://hyperphysics.phyastr.gsu.edu/hbase/pertab/perlewis.
html#c1
Central concept
• The interaction between atoms
(bonding) = ONLY involves valence
electrons
• Think of the inner electrons as being
“locked” tightly in filled energy level
Electron Dot Structures
Represent valence electron
configurations of atom/ions of an
element
Electrons are represented by dots
and arranged in pairs around the
elemental symbol along the four
sides of a square
Can be anywhere from 1 to 8 dots
around an atom
Electron Dot Structures
Electrons are arranged unpaired
until they must be paired (only if
there is more than 4 valence
electrons)
**He is the only element that does
not follow this rule!
Electron Dot Structures
• Why? Because we will use dot
structures of atoms to show bonding.
• Try dot structures for these:
Li
Mg
Si
Kr
Ga
S
Electron Dot Structures
Li
Kr
Mg
Ga
Si
S
Class Work
• Electron Dot
Structures
• Hydrogen
• Calcium
• Aluminum
• Neon
• Sulfur
• Barium
• Silicon
• Oxygen
• Xenon
• Helium
• Tin
• Iodine
• Radon
• Potassium
• Krypton
• Strontium
• Arsenic
Valence Bonding Theory
explains
• How many atoms are connected
• How these atoms are connected
• Shape of the structure
– IONIC = geometry of the structure
– MOLECULAR = shape of the molecule
• Strength of the bond (bond energy)
– Ionic, nonpolar covalent, polar covalent
The Octet Rule
Atoms in compounds tend to gain or
lose electrons (what’s this called?)
to achieve the e- configurations of a
noble gas
8 valence electrons!
Cation: atom with a +
charge
• The LOSS of valence e- produces a
cation
• produced from metals
• lose 1, 2, or 3 electrons easily
• atoms become cations to satisfy the
octet rule
Anion: atom with a charge
• The GAIN of valence e- produces an
anion
• produced from nonmetals
• gains 1, 2, or 3 electrons readily
• atoms become anions in order to
satisfy the octet rule
AGENDA May 13:
• Submit HW
• Notes – Ionic Compounds & Metals
• CW – Properties of Ionic Compounds WS
• HW – Types of Bonds Packet – highlight,
complete all “Reading Checks”and
“Picture This” in margins and 1& 2 on last
page
Ionic bonds and properties
of ionic compounds
• An ionic compound is the result of
the transfer of electrons from one set
of atoms to another and consists
entirely of ions
• Ionic bond - forces of attraction that
bind oppositely charged ions
together
• THEY MUST BE NEUTRAL!
NaCl and ionic bonding
• http://web.jjay.cuny.edu/~acarpi/N
SC/5-bonds.htm
• http://www.visionlearning.com/librar
y/module_viewer.php?mid=55
Electron Dot Structures and
Ionic Bonding
Let’s determine the correct ratio of
atoms that will come together and
form an ionic bond.
1) K & O
2) Li & Cl
3) Mg & N
Electron Dot Structures and
Ionic Bonding
Then complete Ionic Bonding WS
Ionic bonds and properties
of ionic compounds
Conduct electricity
when dissolved in water
Salts
High MP due to
crystalline structure
Properties of ionic bonds
Crystals at
room temperature
Net charge of zero
Composed of
Formula units
• Get out your notes and questions!!
– What questions do you have?
Properties of ionic
compounds
1. Conduct electricity when dissolved
in water (melt)
• What needs to be present in order
to conduct a current?
• when ionic solids dissolve in water,
they break apart into their
component ions
• these ions act as electrical
conductors in water
Properties of ionic
compounds
2. Salts - most ionic compounds are
called salts because of their
crystalline structure
• Crystal - a solid that contains atoms,
ions or molecules in a regular
repeating three dimensional pattern
Notice
• Each Li+ ion is surrounded by four Fions
• Each F- ion is surrounded by four Li+
ions
Lithium Fluoride Again..
Properties of ionic
compounds
3. High melting point due to
crystalline structure
• it will take a lot of energy to break
these highly organized bonds
Properties of ionic
compounds
4. Net charge of zero
• anions and cations connect in a
ratio such that the overall charge of
the ionic compound is zero
• Example: Al+3 + Cl-1 ==> AlCl3
Properties of ionic
compounds
5. Composed of formula units
• a formula unit represents a
compound that is ionically bound
• The lowest whole number ratio of
ions represented in an ionic
compound ex. NaCl instead of
Na2Cl2
Let’s do this together…
• Draw electron dot structures to
illustrate the formation of the
following two ionic compounds…
– Magnesium Chloride
– Aluminum Sulfide
Metallic Bonds
• Definition: Consist of the attraction of the
free-floating valence electrons for the
positively charged metal ions.
• Properties: Metallic bonds involve
“moveable” electrons - this explains many
of the properties of metals
– conductivity
– malleability
– ductility
Metallic Bonds
• http://www.drkstreet.com/resources
/metallic-bonding-animation.swf
AGENDA 25-APR:
• Submit HW
• Notes – Properties of Covalent
Compounds
• CW – Properties of covalent compounds
WS
• HW – pp. 406-408 KT #3, 7-9 RQ # 6, 17-22
Covalent bonds and
properties of covalent compounds
• Covalent bond - forms when
electrons are shared between two
atoms
H + H ==> H2 (H H)
• Atoms can have SINGLE, DOUBLE, or
TRIPLE covalent bonds
Covalent bonds
• Atoms share electrons in a covalent
bond so that each atom has 8
valence electrons & more stability
Covalent bonds
http://web.jjay.cuny.edu/~acarpi/NS
C/5-bonds.htm
Covalent bonds and their
properties
Not very soluble
in water; poor/non
conducting
Share bonding
electrons
Low MP and BP
Properties of covalent bonds
Can be gas,
liquid, or solid
at room temperature
Composed of
molecules
No charged
particles here!
Covalent bonds can be...
1. SINGLE - one pair of e- is shared
between two atoms - shown as a
dash (-) instead of two dots
F-F
• dash is always used in covalent
bonds to show shared electrons NEVER for ionic bonds
Covalent bonds can be...
• Dots represent UNSHARED pairs of
electrons
– lone pairs (around the central bonding
atom & affect molecular shape)
– nonbonding pairs (around the bonded
atoms)
Covalent bonds can be...
2. DOUBLE - two pair of e- is shared
between two atoms
• oxygen = common example
– O2 - each O has 6 valence electrons so
when the O2 bond is formed, it must
share TWO pair of electrons to satisfy
the Octet Rule
–O=O
Covalent bonds can be...
3. TRIPLE - three pair of e- is shared
between two atoms
• nitrogen = common example
– N2 - each nitrogen has 5 valence
electrons so to fulfill the Octet Rule,
three pairs of electrons must be shared
N N
AGENDA 28-APR:
• Submit HW
• Notes – Drawing Covalent Compounds
• CW – Covalent bonding WS
• HW – Covalent bonding WS; TEST NEXT
MONDAY!
Drawing covalent bonds
• Some atoms form single, double, or
triple bonds when forming
compounds to achieve an octet of
electrons
Drawing covalent bonds
HCl: H + Cl ==> H Cl
pair
= shared
Shared pairs can be represented with
a DASH
H-Cl
HCl has THREE unshared pairs
of electrons
Drawing covalent bonds
H2O: 2H + O ==> O H
H
or O H
H
Water has two shared pairs and two
lone pairs of electrons
Drawing covalent bonds
Draw the following covalent
compounds in your notebooks now:
NH3
CH4
CO2
AGENDA 29-APR:
• Submit HW
• Notes - Polarity
• CW – Polarity of Molecules WS
• HW – pp. 406-408 KT #10-13, RQ # 23-28; TEST
MONDAY!
Ionic vs. Covalent bonds
and electronegativity
• What if one atom has a greater
electronegativity than the other but not
enough strength to pull the electron
away all together (form an ionic bond)?
• We land somewhere in the middle with
– polar covalent bonds
– non polar covalent bonds
Polar vs. Nonpolar
Covalent Bonds
• Electronegativtiy measures the nucleus’
ability to attract electrons
• When bonding atoms approach each
other a tug of war begins
Example: HCl H
Cl
H
:Cl
Cl nucleus is stronger so bonding e- are
closer to Cl
Non polar covalent bonds
• Forms when atoms share electrons
equally (like in the H2 example or
CH4)
• Each atom or BONDED atom has
equivalent electronegativity values
Non polar covalent bonds
Polar vs. Non-polar
http://web.jjay.cuny.edu/~acarpi/NS
C/5-bonds.htm
Hydrogen – non-polar
Water - polar
AGENDA 30-April:
• Submit HW
• Notes – Molecular Geometry
• CW – Shapes of Molecules WS #1-6
• HW – Shapes of Molecules #7-12; TEST
MONDAY!
Three dimensional
chemistry
• REMEMBER
– electrons = same charge = repel each other
– Lone pair electrons also repel
• because electron pairs repel, molecules
adjust their shape so that the valence
electron pairs are as far apart as possible
= VSEPR theory
Methane (tetrahedral, CH4)
Pyramidal (ammonia, NH4)
Bent (water, H2O)
AGENDA 1-April:
• Submit HW
• Molecular Geometry Activity
• HW – Review Study Guide; TEST
MONDAY!
2-MAY:
• Questions from Study Guide?
• CW: Web Quest Review