Chemical Bonding

I. Introduction  A. Types of Chemical Bonds – forces that hold two atom together 1. Ionic Bonds – occur b/w a metal & a nonmetal 2. Covalent Bonds – occur b/w 2 nonmetals & in polyatomic ions  a. Polar Covalent Bonds -

 B. Distinguishing b/w Types of Bonds 1. Electronegativity – ability of an atom to attract electron’s to itself.

2. Bond Polarity: You can use the element’s electronegativities to determine the polarity of the bond – Just find the difference b/w the 2 numbers  0 – 0.4Covalent bond  0.41 – 0.99Polar Covalent bond  > 1.00Ionic bond

Determine the Polarity!  1. H – O  2. C – N  3. K – F  4. S – O  5. Al - P

What Polarity Looks Like

3. Dipole Moments – When a bond is polar… 1 side of the molecule is more positive and the other side is more negative.  Why? Because the electrons are being pulled toward the more electronegative element.

Dipole Moments

Why is Water’s Dipole Moment So Important?  It has a huge affect on its properties!  It’s so important, it has a specific name, it’s called HYDROGEN BONDING.  It is crucial to life on Earth!  Polar water molecules can surround & attract positive & negative ions which allows materials to dissolve in water!

 It’s polarity also means that water molecules are attracted to each other  A LOT of ENERGY is needed to change H 2 O from a liquid to a gas because the attraction must be overcome to separate 1 H 2 O molecule from another.  So what?!?!This causes water on Earth, at Earth’s temperatures, to remain a liquid. OTHERWISE, it would all be a gas and the oceans would be empty!!!!

II. Ionic Bonds  A. A strong bond caused by the transfer of electrons from a cation (metal) to an anion (nonmetal). 1. Why? The driving force behind this bonding is that all elements want to have a completely filled outermost energy level! [OCTET RULE]  a.) These outermost electrons are called the VALENCE ELECTRONS  b.) Metals LOSE valence electrons to be stable.  c.) Nonmetals GAIN valence electrons to be stable.

Valence Electrons 1e-8e- 2e-3e-4e-5e-6e-7e- 2e- 1e- 2e-

Let’s try it!  1. Na and O  2. Al and F  3. Ca and S  4. Mg and P

 B. Ionic Bonding And Structures of Ionic Compounds 1. Ionic compounds are  a. very stable, huge amounts of energy necessary to break them apart  b. high melting & boiling points NaCl has a melting point = ~800°C

2. Structures of Ionic Compounds  a. When you write the formula for an ionic compound, you are writing its empirical formula.  b. In reality, the actual solid contains tremendous amounts & equal numbers of cations and anions packed together so that the attractions b/w them are maximized. 1.) Remember that cations are always smaller than anions. WHY?

III. Covalent Bonding  A. Sharing electrons! 1. All bonding involves valence electrons ONLY!!!!!! 2. Covalent bonds occur when 2 atoms (usually nonmetals) share electrons. 3. LEWIS STRUCTURE – a representation of a molecule that shows how the valence electrons are arranged among the atoms in the molecule.  Thought up by G.N. Lewis while teaching a chemistry class in 1902.

See attached page for writing Lewis Structures!

 B. Structures – VSEPR Model 1. Valence Shell Electron Pair Repulsion Model  a. Useful for predicting the geometric shape of molecules formed from nonmetals!  b. The structure around a given atom is determined by minimizing repulsions between electron pairs.

Metallic Bonding  How atoms are held together in the solid.  Metals hold onto their valence electrons very weakly.  Think of them as positive ions floating in a sea of electrons!

Sea of Electrons!  Electrons are free to move through the solid.  Metals conduct electricity

Metals are malleable!  Hammered into shape (bend).  Ductile - drawn into wires

Malleable  Electrons allow atoms to slide by

Alloys  Solutions made by dissolving metal into other elements- usually metals.  Melt them together and cool them.  If the atoms of the metals are about the same size, they substitute for each other  Called a substitutional alloy

Metal A Metal B +  Substitutional alloy Bronze – Copper and Tin Brass- 60 % Copper 39% Zinc and 1%Tin 18 carat gold- 75% gold, 25%Ag or Cu

Alloys  If they are different sizes the small one will fit into the spaces of the larger one  Called and interstitial alloy

Metal A +  Metal B Interstitial Alloy Steel – 99% iron 1 % C Cast iron- 96% Iron, 4%C

Alloys  Making an alloy is still just a mixture  Blend the properties  Still held together with metallic bonding  Most of the metals we use daily are alloys.  Designed for a purpose