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Regents Chemistry

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Title: Regents Chemistry


1
Regents Chemistry
  • Agenda
  • Start Chapter 12 - Chemical Bonding
  • Bonding worksheet
  • HW Finish worksheet

2
What 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

3
What 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
4
Bonds 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)

5
Types of bonds
  • Ionic bonds - typically formed between metals and
    nonmetals
  • Covalent bonds - typically formed between
    nonmetals
  • Metallic bonds - formed between metals

6
Ionic 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

7
Ionic 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!
8
Ionic Bonds
  • Na looses an electron and chlorine gains it!
  • They do this to achieve an octet!

Na
Cl
9
Covalent Bonds
  • Covalent Bonds
  • exist between nonmetals bonded together
  • form when atoms of nonmetals share electrons
  • electrons can be shared equally or unequally

10
Covalent 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
-

11
Metallic Bonds
  • Metallic bonds exist between metals
  • Occur when two metals, usually the same metal,
    are bonded together

12
Regents Chemistry
  • Electronegativity

13
How 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

14
Electronegativity
  • 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

15
Electronegativity
  • 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

16
Determining 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)

17
Examples
  • 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
  • H-F
  • NaCl
  • O2
  • KBr

Worksheet
18
Regents Chemistry
  • Intro to valence electrons

19
Electrons 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

20
The 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

21
Periodic 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

22
Sharing 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

23
Nonmetals share
  • Nonmetals share electrons to reach eight valence
    electrons
  • Single, double and triple bonds can be formed by
    sharing electrons

24
Metals 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

25
Lewis 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

26
Example of a Lewis Structure
C
CH4 Covalent bonds
H
H
C
H
H
H
27
Regents Chemistry
  • Lewis Structures

28
Lewis 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
29
Single 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
30
Lewis 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
31
Lewis 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

32
Lewis 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

33
Writing 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

34
Lewis Structures Covalent Bonds
  • Examples

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
35
Lewis Structures Covalent Bond Practice Examples
.. HBr
HBr
CF4
Worksheet
36
Regents Chemistry
  • Ionic Lewis Structures
  • Multiple bonds in Lewis Structures
  • Polyatomic ion Lewis Structures and Resonance

37
Lewis 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
38
Examples of Ionic Lewis Structures
  • Draw Lewis Structures for the following
  • NaCl
  • LiBr
  • KI

39
Multiple 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
40
Multiple 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
41
Example of Multiple Bonds
Nitrogen
N N
N N
We now meet the octet rule!
42
Multiple Bonds
  • Between atoms of different elements
  • CO2

C
O
O
O C O
We must use double bonds to meet the octet rule!
43
Lewis 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)
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