Title: Regents Chemistry
1Regents Chemistry
- Agenda
- Start Chapter 12 - Chemical Bonding
- Bonding worksheet
- HW Finish worksheet
2What is bonding?
- Bonding is the glue that hold two or more
elements together - This glue is most likely formed as a result of
a chemical reaction - Bonding and molecular structure play a central
role in determining the course of chemical
reactions
3What is a bond?
- A bond can be thought of as a force that holds
groups of two or more atoms together and makes
them function as a unit - Example water
O
Bonds require energy to break and release energy
when made
H
H
4Bonds and Energy
- BREAKING BONDS requires energy
- You Must Heat Wood to get it to react with oxygen
(ENDOTHERMIC) - MAKING BONDS releases energy
- Once the bonds are broken, they form new products
and this process releases heat (EXOTHERMIC)
5Types of bonds
- Ionic bonds - typically formed between metals and
nonmetals - Covalent bonds - typically formed between
nonmetals - Metallic bonds - formed between metals
6Ionic Bonds
- Ionic substances are formed when an atom that
loses electrons relatively easily reacts with an
atom that wants electrons - We call these substances ionic compounds and
result when a metal reacts with a nonmetal - Ionic bonds are strong
7Ionic Bonds
- Na and Cl
- Na is a metal and likes to lose one electron
- Cl is a nonmetal and likes to gain one electron
- the final ionic compounds is NaCl
Na
Cl-
NaCl
The electrostatic interaction keeps them
together!
8Ionic Bonds
- Na looses an electron and chlorine gains it!
- They do this to achieve an octet!
Na
Cl
9Covalent Bonds
- Covalent Bonds
- exist between nonmetals bonded together
- form when atoms of nonmetals share electrons
- electrons can be shared equally or unequally
10Covalent Bonds Cont
- Covalent bonds that have elements that share
electrons equally are simply said to have a
covalent type of bond - Covalent bonds that share electrons unequally are
said to have a polar covalent type of bond - The unequal sharing results in a bond polarity
F
H
-
11Metallic Bonds
- Metallic bonds exist between metals
- Occur when two metals, usually the same metal,
are bonded together
12Regents Chemistry
13How can we tell really tell which type of bond we
have?
- Electronegativity is the relative ability of an
atom in a molecule to attract shared electrons to
itself - This tells us what type of bond we have
- Covalent, polar covalent or ionic
- Electronegativity values are determined by
measuring the polarities of bonds between various
elements to determine a specific value for each
element
14Electronegativity
- Electronegativity values for each element are
obtained by using the Periodic Table - In fact, there is a general trend in
electronegativity we observe in the Periodic
Table - Electronegativity values increase across and up
the Periodic Table - See table on pg. 332
15Electronegativity
- We take the difference between the
electronegativity values to determine exactly
what type of bond exists, in essence the polarity
of the bond - See table 12.1
16Determining Bond Polarity
- If the difference between the electronegativity
values is - 0.0 0.5 covalent bond (equal sharing)
- 0.6 1.6 polar covalent bond (unequal sharing)
- 1.7 up ionic bond (transferring electrons)
17Examples
- Use your Reference Tables to determine the
difference in electronegativity values and the
type of bond for each of the following - H-H
- H-Cl
- H-O
- H-S
Worksheet
18Regents Chemistry
- Intro to valence electrons
19Electrons in an atom
- Electrons surround the nucleus of an atom in
specific energy levels or shells - Each level can hold only a certain amount of
electrons - It is an atoms ability to the lose, gain or share
electrons from its outer shell that determine its
reactivity
20The outer shell
- The outer shell in an atom contains the valence
electrons - Valence electrons can be lost, gained or shared
to have eight electrons in the outer shell - Each group on the table tells the number of
valence electrons
21Periodic Table
- Groups 1, 2, 13, 14, 15, 16, 17, 18 have
1,2,3,4,5,6,7,8 valence electrons, respectively - We will not consider the transition metals
- See periodic table
22Sharing to reach the Octet Rule
- The octet rule states that an atom cannot have
more than 8 electrons in its outer shell - Valence electrons are lost, gained or shared with
other atoms to attain 8 electrons in the outer
shell - Eight valence electrons means a filled and happy
shell - like the noble gases
23Nonmetals share
- Nonmetals share electrons to reach eight valence
electrons - Single, double and triple bonds can be formed by
sharing electrons
24Metals non-metals lose/gain e-
- metals and nonmetals interact by losing and
gaining electrons to reach 8 electrons (filled
outer shell) - The oxidation states on the periodic table
represent this desire to move electrons - ex K want to lose 1 electron to reach noble
gas configuration of eight electrons
25Lewis structures your assignment
- The reading and problems focus on drawing Lewis
structures - Lewis structures are a means to represent bond
formation between atoms - Covalent bonded compounds have different Lewis
structures than Ionic bonded compounds
26Example of a Lewis Structure
C
CH4 Covalent bonds
H
H
C
H
H
H
27Regents Chemistry
28Lewis Structures
- The Lewis Structure is a representation of a
molecule that shows how the valence electrons are
arranged among the atoms in a molecule - We used dots around the elemental symbol to
represent the valence electrons
C
29Single Lewis Structure - Practice
- Draw four lone electrons first (if necessary)
them pair them up - Draw Lewis Structures for the following atoms
Br
Al
Na
Be
30Lewis Structures for Ionic Compounds
- For Lewis Structures of ionic bonds the atoms are
not joined but draw next to each other
-
example KBr
Br
K
Bromine gains an electron to achieve the noble
gas configuration of Krypton
Potassium loses an electron to achieve the noble
gas configuration of Argon
31Lewis Structures Covalent Bonds
- Hydrogen forms stable molecules when it shares
two electrons - Two electrons fill Hydrogens valence shell
- Helium does not form bonds because its valence
shell is already filled it is a noble gas - Second row non-metals Carbon through Fluorine
from stable molecules when surrounded by eight
electrons the Octet Rule
32Lewis Structures Covalent Bonds
- Valence electrons in covalent bonds can either be
bonding pairs, if involved directly in the bond
or lone pairs if not involved in the bond
33Writing Lewis Structures - Rules
- Obtain the total sum of the valence electrons
from all of the atoms - Use one pair of electrons to form a bond between
each pair of bound atoms. For convenience, a
line (instead of a pair of dots) can be used to
indicate each pair of bonding electrons - Arrange the electrons to satisfy the duet rule
for hydrogen and the octet rule for second row - non metals
34Lewis Structures Covalent Bonds
Step 1) 8 total valence e- total Step 2) Draw
one pair of electrons per bond
8-6 2 left Step 3) Arrange the remaining
electrons according to
octet rule
PH3
H l H P H
H
P
H
H
35Lewis Structures Covalent Bond Practice Examples
.. HBr
HBr
CF4
Worksheet
36Regents Chemistry
- Ionic Lewis Structures
- Multiple bonds in Lewis Structures
- Polyatomic ion Lewis Structures and Resonance
37Lewis Structures for Ionic Compounds
- For Lewis Structures of ionic bonds the atoms are
not joined but draw next to each other
-
example KBr
Br
K
Bromine gains an electron to achieve the noble
gas configuration of Krypton
Potassium loses an electron to achieve the noble
gas configuration of Argon
38Examples of Ionic Lewis Structures
- Draw Lewis Structures for the following
- NaCl
- LiBr
- KI
39Multiple Bonds and Lewis Structuresreview first
- We have seen how to draw Lewis Structures for
molecules with single bonds - For example
- NH3
8 total valence e- 3 bonds x 2e- 6 bonding 2 e-
left over
- Sum the total
- valence e-
- Subtract number
- of bonding e-
- Place remaining
- valence e-
H
H
N
H
40Multiple Bonds
- Between atoms of the same element
- Example
- Oxygen
- O O
Also a Lewis Structure
O O
Just O O is called a structural model
41Example of Multiple Bonds
Nitrogen
N N
N N
We now meet the octet rule!
42Multiple Bonds
- Between atoms of different elements
- CO2
C
O
O
O C O
We must use double bonds to meet the octet rule!
43Lewis Structures for Polyatomic Ions and
Resonance Structures
- Read pg. 344 (bottom) to 349 and answer questions
a-g in example - 12.4 (pg. 347) and a-i in the Self Check
exercise 12.4 (pg. 348)