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Regents Chemistry. Agenda Start Chapter 12 - Chemical Bonding Bonding worksheet HW: Finish worksheet . 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

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Regents chemistry
Regents Chemistry

  • Agenda

    • Start Chapter 12 - Chemical Bonding

    • Bonding worksheet

    • HW: Finish worksheet


What is bonding
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


What is a bond
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


Bonds and energy
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)


Types of bonds
Types of bonds

  • Ionic bonds - typically formed between metals and nonmetals

  • Covalent bonds - typically formed between nonmetals

  • Metallic bonds - formed between metals


Ionic bonds
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


Ionic bonds1
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!


Ionic bonds2
Ionic Bonds

  • Na looses an electron and chlorine gains it!

  • They do this to achieve an octet!

Na

Cl


Covalent bonds
Covalent Bonds

  • Covalent Bonds

    • exist between nonmetals bonded together

    • form when atoms of nonmetals share electrons

    • electrons can be shared equally or unequally


Covalent bonds con t
Covalent Bonds Con’t

  • 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

-

+


Metallic bonds
Metallic Bonds

  • Metallic bonds exist between metals

  • Occur when two metals, usually the same metal, are bonded together


Regents chemistry1
Regents Chemistry

  • Electronegativity


How can we tell really tell which type of bond we have
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


Electronegativity
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


Electronegativity1
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


Determining bond polarity
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)


Examples
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


Regents chemistry2
Regents Chemistry

  • Intro to valence electrons


Electrons in an atom
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


The outer shell
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


Periodic table
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


Sharing to reach the octet rule
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


Nonmetals share
Nonmetals share

  • Nonmetals share electrons to reach eight valence electrons

  • Single, double and triple bonds can be formed by sharing electrons


Metals non metals lose gain e
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


Lewis structures your assignment
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


Example of a lewis structure
Example of a Lewis Structure

C

CH4

Covalent bonds

H

H

H

C

H

H


Regents chemistry3
Regents Chemistry

  • Lewis Structures


Regents chemistry

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


Regents chemistry

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


Regents chemistry

Lewis Structures for Ionic Compounds

  • For Lewis Structures of ionic bonds the atoms are not joined but draw next to each other

example:

KBr

-

K+

[ Br ]

Bromine gains an

electron to achieve

the noble gas configuration

of Krypton

Potassium loses an

electron to achieve

the noble gas configuration

of Argon


Regents chemistry

Lewis Structures – Covalent Bonds

  • Hydrogen forms stable molecules when it shares two electrons

  • Two electrons fill Hydrogen’s 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


Regents chemistry

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


Regents chemistry

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


Regents chemistry

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

H

P

H



Regents chemistry4
Regents Chemistry

  • Ionic Lewis Structures

  • Multiple bonds in Lewis Structures

  • Polyatomic ion Lewis Structures and Resonance


Regents chemistry

Lewis Structures for Ionic Compounds

  • For Lewis Structures of ionic bonds the atoms are not joined but draw next to each other

example:

KBr

-

K+

[ Br ]

Bromine gains an

electron to achieve

the noble gas configuration

of Krypton

Potassium loses an

electron to achieve

the noble gas configuration

of Argon


Regents chemistry

Examples of Ionic Lewis Structures

  • Draw Lewis Structures for the following:

    NaCl

    LiBr

    KI


Regents chemistry

Multiple Bonds and Lewis Structures…review 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

N

H

H


Regents chemistry

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


Regents chemistry

Example of Multiple Bonds

Nitrogen

N N

N N

We now meet the octet rule!


Regents chemistry

Multiple Bonds

  • Between atoms of different elements

  • CO2

O

C

O

O = C = O

We must use double bonds to meet the octet rule!


Regents chemistry

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)