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Regents Chemistry Agenda Start Chapter 12 - Chemical Bonding

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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)


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