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+ Cl- NaCl + Na and Cl The electrostatic interaction
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 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 - +

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
CH4
Covalent bonds H H H C 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. K+ [ Br ] - 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

31. 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

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 H P H

35. H:Br: HBr CF4 Lewis Structures – Covalent Bond Practice Examples .. ··
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 - 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

38. Examples of Ionic Lewis Structures
Draw Lewis Structures for the following:
NaCl
LiBr KI

39. 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 H N H H

40. Multiple Bonds O = O Between atoms of the same element Example Oxygen
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 O C 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)