Chapter 4: Chemical Bonding When Atoms Collide

Unit Objectives To be able to: Explain why some elements react (form bonds.) Explain why some elements react (form bonds.) Explain the difference between an ionic & a covalent bond. Explain the difference between an ionic & a covalent bond. Demonstrate e- reconfiguration when a simple compound is formed. Demonstrate e- reconfiguration when a simple compound is formed. Explain how interparticle forces affect the properties of ionic & covalent compounds. Explain how interparticle forces affect the properties of ionic & covalent compounds.

Sodium (metal)  Solid  Good conductor of electricity & heat  VERY reactive  Silvery/luster  Malleable, soft  Melting point-low 98 C  Uses: never pure in nature b/c sooooo reactive!

Chlorine (nonmetal)  Poisonous, green gas  Disinfectant  Reactivity-very reactive. Rarely found pure in nature b/c sooo reactive.

Salt (NaCl)  Edible, common food additive  White  Crystalline solid  Reactivity-not reactive/ very stable  Brittle  Conductivity- as a solid, poor conductor  As a liquid or in aqueous solution, excellent conductor = ELECTROLYTE

Carbon (nonmetal)  room temperature  Fairly rm temperature. Very reactive at high temperatures.  Most of the compounds in living things made from carbon.  Brittle/hard (charcoal/diamond)  High melting & boiling points

Oxygen (Nonmetal)  Gas at room temp  Colorless, odorless, tasteless  21% of atmosphere  Very low MP/BP (-183 C BP)  Slightly soluble in water  Reactive, combines w/many elements  Most abundant element in earth’s crust

Carbon dioxide  Somewhat soluble in water  Poor conductor  Fairly unreactive  Uses  some fire extinguisher b/c it won’t burn  Photosynthesis  Nearly all the food for all living things comes thru photosynthesis  Trees pull CO 2 out of the air & decrease greenhouse effect

Hydrogen  Odorless, tasteless, colorless  Very reactive (ex: Hindenburg)  Low MP & BP  Gas at rm temperature  Slightly soluble in water  not a conductor  Lightest and most abundant element in universe

Water  Liquid at room temp  Stable-doesn’t react w/most things  examples  Chemical rxns in human body take place in water  `Necessary for photosynthesis

Classwork On p 59 of I.N.  Analyze CO2  Compare the properties of C, O, and CO2

What is Happening?  Watch the videos.  What is happening in all of these reactions ? Hydrogen balloon burning 2H 2 + O 2  2H 2 O sodium metal & chlorine Na + Cl  NaCl sodium iodide & mercury (II) chloride 2NaI + HgCl 2  2NaCl + HgI 2

The Noble Gases  All of them occur in nature  BUT no compounds containing them ever found in nature  Analysis: they are unreactive/stable as they are  Question: Why are they so stable?  Data: When we look at their electron configurations, they all* have 8 valence e-s! (*except He)

The Noble Gases (cont.)  Something about having 8 valence e-s (or 2, if you are a small atom) makes you stable, “Happy”  Called “Noble Gas Configuration ”

Atoms can Get NGC in one of 2 ways (cont.) 1. Share e-s (COVALENT bond)  This occurs when the 2 atoms in the bond pull on their e-s w/the same (or similar) strength  Typically occurs between 2 ___________.

Atoms can Get NGC in one of 2 ways (cont.) 2. Lose/gain e-s (IONIC bond)  This occurs when the 2 atoms in the bond pull on their e-s w/different strengths  Typically occurs btwn a _____ & a _____.

3 “Classes” of Elements  Metals = pink Conductors? Yes! Hold e-s? Loosely How many V.E’s? 1-3  Nonmetals = green Conductors? No! Hold e-s? Tightly How many V.E.’s? 5-7  Metalloids = blue “In between”

Ions & the Octet Rule  Ions are charged particles that have lost or gained e-s to satisfy the octet rule (8 e-s)  They will typically form based on what requires the smallest gain or loss of e-s to complete an octet.

Formation of an ionic bond  When e-s are lost by 1 atom & gained by another, one atom develops a + charge (“cation”) and the other develops a – charge (anion)  Attraction between ions is what forms bond.  Note: you will not always have a 1:1 ratio of + to - ions.  Ex: MgI 2 -see next slide

Formation of MgI .Mg. +:I: → Mg. + + :I: - (are they happy?) Mg. +:I: :I: → Mg 2+ + :I: - :I:

ACTIVITY: Egg Carton Atoms Ionic Bonding MATERIALS Egg carton (“atom”) Egg carton (“atom”) Candy or marbles (“electrons”) Candy or marbles (“electrons”) Data Sheet Data Sheet

Rules for “Placing” e-s  Place e-s in lowest available E.L.  Fill an E.L. before putting e-s in next available E.L.  Only 1 “electron” per space in egg carton.

Your Goal:”Happy” Atoms Ionic Compound With your partner, obtain NGC for BOTH of your atoms!  Each atom will have EITHER  A full 1st E.L. & no e-s in 2nd E.L. OR  A full 1st and 2nd E.L.  One will donate e-s & one will receive e-s.

Step 1: Your Atom  Count # of “e-s”  Identify element  Identify column/group#  What is valence level?  How many valence e-s?  How many e-s must be gained to obtain NGC?  How many e-s must be lost to obtain NGC?  How many e-s lost or gained (Which is easier?)

Step 2: Both Atoms  Share your information with your partner & record on Data Table.  Decide how you can help each other obtain NGC by giving or receiving e-s.  Make the e- switch! & observe NGC.

Step 3: Discuss Results

Now it’s your turn!  Partner 1: 3 e-s  Partner 2: 9 e-s  (Identify your elements first.)  With your new set of “electrons,” form an ionic compound with your partner.  Record your data and your partner’s.  Be prepared to discuss.

Results of Example 2: Li & F

Summary so Far  Atoms that collide may bond if they can help each other become more stable.  Noble gases are stable the way they are-8 valence e-s in most cases (“octet”).  All other elements want to be like noble gases.  Two ways to get “NGC”  Transfer e-s if strength of 2 elements is very unequal (ionic bond)  Share e-s if strength of 2 elements is pretty equal (covalent bond)

“Isoelectronic”  Term used to describe atoms/ions with the same e- configuration  Ex: F- and Ne  Both have 2 e-s in the 1 st energy level  Both have 8 electrons in the 2 nd energy level  Ex: He and H-  Both have 2 electrons in the exact same arrangement

Formulas  Tell us:  the elements that make up the compound  the # of atoms of each element in a unit of the compound  The smallest unit of an Ionic Compound is called a “Formula Unit”  The smallest unit of a Covalent compound is called a Formula Unit or “Molecule”

To Explain Why…  Elements in an ionic compound occur in a specific ratio, BUT  You never have just 1 Na and 1 Cl, for example  Instead YOU HAVE A CRYSTALLINE STRUCTURE (“lattice”) (see p 134)

Crystal Arrangement Causes Behavior of Ionic Compounds  Each ion is “locked in” in 6 directions (ex: each Na+ is surrounded by 6 Cl-)  Giant Ionic Lattice Giant Ionic Lattice Giant Ionic Lattice  Rotating NaCl Lattice Rotating NaCl Lattice Rotating NaCl Lattice e Fig p 570

Properties of Ionic Compounds  Brittle  Cubic in shape  Very stable  Solids (high MP, BP.)  Very soluble in water  Electrolyte

Ionic Compounds-Electrolytes  In order for something to be a good conductor, it must have freely moving charged particles.  Ions are charged particles that are “locked in” when in solid form…  BUT when they are melted or dissolved in water, BOY CAN THEY MOVE!

Interparticle Forces  The attraction between formula units (particles of a substance) is called: “INTERPARTICLE FORCES”  strong IP forces between adjacent NaCl units, for example.  weak attraction between adjacent molecules of covalent compounds, H2O, for example.

Interparticle Forces in Covalent Compounds  Molecules have little to no charge so they are attracted v. weakly to one another  This makes covalent compounds  Liquids/gases (almost always!)  Have low MP/BP

Interparticle Forces in Covalent Compounds, cont.  Not soluble in water (or very slightly) ex: oil, gas, CO2  poor conductors-WHY??? Think-Pair-Share!!!

Why covalent compounds are lousy conductors.  In order for something to be a conductor, it must have freely- moving charged particles.

Types of Covalent Bonds  Single Bond- When a pair of electrons is shared  Double Bond….you tell me!  Triple Bond…

Examples of Covalent Compounds  The properties of covalent compounds vary more widely than those of ionic cpds.  Ex: butter, water, CO2, gasoline, candle wax, table sugar, alcohol

Activity: Egg Carton Atoms Covalent Bonding Your Goal: With your partner, obtain NGC for both your atoms by sharing electrons! NOTE: Overlap cartons to represent sharing of e-s.

Practice Together: H 2  Each partner is going to represent a H atom.  Let’s answer the Qs together.

Step 2: Both Atoms  Remove “e-s” from rows that will be overlapped.  Overlap 1 carton’s row/s with your partner’s.  Place the removed e-s from both atoms in the overlapped rows. -NGC!

Step 1: Your Atom, F  Count # of “e-s”  Identify element  Identify column/group#  What is valence level?  How many valence e-s?  How many e-s must be gained to obtain NGC?  This is the # of rows that must be overlapped to share e-s with your partner.

Step 2: Both Atoms  Remove “e-s” from rows that will be overlapped.  Overlap 1 carton’s row/s with your partner’s.  Place the removed e-s from both atoms in the overlapped rows. -NGC!

Solution

More Practice  Each person makes their atom.  Next form covalent compound with neighbor.  Oxygen  Nitrogen

Answers to practice  Oxygen involves the overlap of 2 rows in each carton. (double bond)  Nitrogen involves the overlap of 3 rows in each carton. (triple bond)

Quiz  Ionic bonds are formed by the ______ of electrons.  Covalent bonds are formed by the ________ of electrons.  CO is a/n ionic/covalent compound.  NaF is a/n ionic/covalent compound.