Chemical Bonding Chem I: Chapters 4, 5, 9 Chem IH: 7, 8, 9
Unit Objectives To be able to: • Explain why some elements react (form bonds.) • Explain the difference between an ionic & a covalent bond. • Demonstrate e- reconfiguration when a simple compound is formed. • 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) Solid @ room temperature Fairly unreactive @ 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 CO2 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 2H2 + O2 2H2O sodium metal & chlorine Na + Cl NaCl sodium iodide & mercury (II) chloride 2NaI + HgCl2 2NaCl + HgI2
The Chemical Bond • The force that holds two atoms together • Occurs using valence electrons
Lewis Dot Diagram Definition: System of showing the valence e-s for an atom Help us predict bonds
Lewis Dot Diagram, cont. 1) Element symbol in middle 2) Valence e-s represented by dots • Place v.e.-s around the element symbol in 4 locations • Above • Below • Left • Right • Don’t pair up any, until 1 in each location.
Lewis Dot Diagram, cont. Practice: Together: let’s do LDD for Hydrogen, helium, You practice: lithium, beryllium, boron, carbon, nitrogen, oxygen, fluorine, neon.
The Noble Gases All occur in nature BUT no compounds containing them are ever found in nature Common denominator is that they all have 8 valence e-s. (*except He, which has 2) This is what makes them stable/unreactive This is called “Noble Gas Configuration” (NGC)
All “Other” Elements All other elements “want” NGC, so they can be stable.
Atoms can Get NGC in one of 2 ways (cont.) 1. Lose/gain e-s (IONIC bond) • This occurs when the 2 atoms in the bond pull on their e-s w/different strengths • Big EN difference • Typically occurs btwn a _____ & a _____.
Atoms can Get NGC in one of 2 ways (cont.) 2. 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 • Small EN difference • Typically occurs between 2 ___________.
3 “Classes” of Elements(Review- Do Not Copy) • 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. Ex: Na Na+ + e- Ex: Cl + e- Cl-
Formation of Ions The charge on an ion is called its “oxidation number”
Formation of Ions, cont. • Metals tend to lose electrons • Have + oxidation number • Called “cations” • Metal ions are given the element name • Ex: Na+ = “sodium ion”
Formation of Ions, cont. • Nonmetals tend to gain electrons • Have – oxidation number • Called “anions” • Nonmetal ions are given the element name w/an “-ide” ending • Ex: O2- = “oxide ion”
TO DO: Label Your Periodic Table • Label Groups 1, 2, 3, 16, 17 w/the oxidation number of each group. Group #Oxidation # 1 +1 2 +2 3 +3 16 -2 17 -1
Practice Together, write the arrow orbital diagram for a sodium atom. Now draw the arrow orbital diagram for a sodium ion. Identify the noble gas that has the same notation as a sodium ion. Write the symbol for a sodium ion
Formation of an ionic bond • When e-s are lost by 1 atom they are gained by another. Therefore, cations & anions are formed at the same time. • Occur between elements w/great differences in EN. • Usually a metal & a nonmetal • Ex: Na & Cl
Formation of an ionic bond, cont. Attraction between ions is what forms bond. Cl-1 Na+1 Cl-1 Na+1 Cl-1 Na+1 Cl-1 Na+1 Cl-1 Na+1 Cl-1 Na+1 Cl-1 Na+1 Cl-1 Na+1 Cl-1 Na+1 Cl-1 Na+1 Practice: Draw Lewis Dot Diagrams for sodium and chlorine ATOMS. Then show what happens to form sodium & chlorine IONS. (BONUS: What NG is each ion like?)
Formation of an ionic bond, cont. • Note: you will not always have a 1:1 ratio of + to - ions. • Ex: MgI2 -see next slide
Formation of MgI2 .. .. • .Mg. + :I: → Mg.+ + :I: - (are they happy?) . .. .. .. .. .. • .Mg. + :I: :I: → Mg2+ + :I: - :I:- . . .. ..
ACTIVITY: Egg Carton AtomsIonic Bonding MATERIALS • Egg carton (“atom”) • Candy or marbles (“electrons”) • 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” AtomsIonic 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.
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.
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 1st energy level • Both have 8 electrons in the 2nd 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 e Fig 22-25 p 570 • Each ion is “locked in” in 6 directions (ex: each Na+ is surrounded by 6 Cl-) • Giant Ionic Lattice • Rotating NaCl Lattice
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!!!