Introduction to Bonding Topic #13 Essential Question: What are all the differences and similarities between covalent bonds and ionic bonds?

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 HH Bonds require energy to break and release energy when made

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 bonding results from the transfer of electrons. Then, the opposite charges attract each other. Ionic bonds are strong

Ionic Bonds Na and Cl –Na is a metal and likes to lose one electron and form a +1 ion. –Cl is a nonmetal and likes to gain one electron and form a -1 ion. –the final ionic compounds is NaCl Na + Cl - + NaCl The electrostatic interaction keeps them together!

Ionic Bonds They do this to achieve an octet!

Covalent Bonds –exist between nonmetals bonded together –form when atoms of nonmetals share electrons –electrons can be shared equally or unequally –The unequal sharing results in polar molecules

Metallic Bonds Metallic bonds exist between metals Occur when two metals, usually the same metal, are bonded together “sea of electrons” “delocalized electrons” ttp:// JsE&feature=bf_next&list=PLBFE28832E57 7A62Bttp:// JsE&feature=bf_next&list=PLBFE28832E57 7A62B

Regents Chemistry Electronegativity

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 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

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 Electronegativity

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 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 O 2 KBr Worksheet

Regents Chemistry Intro to valence electrons

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

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 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 CHH H H C H CH4 Covalent bonds

Regents Chemistry Lewis Structures

b The Lewis Structure is a representation of a molecule that shows how the valence electrons are arranged among the atoms in a molecule b We used dots around the elemental symbol to represent the valence electrons C

Single Lewis Structure - Practice b Draw four lone electrons first (if necessary) them pair them up b Draw Lewis Structures for the following atoms NaBe Al Br

Lewis Structures for Ionic Compounds b For Lewis Structures of ionic bonds the atoms are not joined but draw next to each other [ Br ]K+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 example: KBr

Lewis Structures – Covalent Bonds b Hydrogen forms stable molecules when it shares two electrons b Two electrons fill Hydrogen’s valence shell b Helium does not form bonds because its valence shell is already filled; it is a noble gas b Second row non-metals Carbon through Fluorine from stable molecules when surrounded by eight electrons – the Octet Rule

Lewis Structures – Covalent Bonds b 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

Writing Lewis Structures - Rules b Obtain the total sum of the valence electrons from all of the atoms b 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 b Arrange the electrons to satisfy the duet rule for hydrogen and the octet rule for second row non metals non metals

Lewis Structures – Covalent Bonds b Examples PH 3 PH 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 H H H l H– P –H

Lewis Structures – Covalent Bond Practice Examples HBr.. H:Br: ·· CF 4 Worksheet

Regents Chemistry –Ionic Lewis Structures –Multiple bonds in Lewis Structures –Polyatomic ion Lewis Structures and Resonance

Lewis Structures for Ionic Compounds b For Lewis Structures of ionic bonds the atoms are not joined but draw next to each other [ Br ]K+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 example: KBr

Examples of Ionic Lewis Structures b Draw Lewis Structures for the following: NaClLiBrKI

Multiple Bonds and Lewis Structures…review first b We have seen how to draw Lewis Structures for molecules with single bonds For exampleFor example NH3 NH3 1.Sum the total valence e - 2.Subtract number of bonding e- 3.Place remaining valence e - 8 total valence e- 3 bonds x 2e- = 6 bonding 2 e - left over H HHN

Multiple Bonds b Between atoms of the same element b Example OxygenOxygen O O O O O = O Also a Lewis Structure Just O = O is called a structural model

Example of Multiple Bonds Nitrogen N We now meet the octet rule!

Multiple Bonds b Between atoms of different elements b CO 2 COO O = C = O We must use double bonds to meet the octet rule!

Lewis Structures for Polyatomic Ions and Resonance Structures b 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) 12.4 (pg. 347) and a-i in the Self Check exercise 12.4 (pg. 348)