1. 1 CHEMICAL BONDING w/ Emch Cocaine

2. 2 Chemical Bonding Problems and questions — How is a molecule or polyatomic ion held together? What’s the difference between ionic, covalent, and metallic bonds? How is bond type related to chemical and physical properties?

3. 3 Review of Chemical Bonds There are 3 forms of bonding:There are 3 forms of bonding: _________—complete transfer of 1 or more electrons from one atom to another (one loses, the other gains) forming oppositely charged ions that attract one another, producing large crystals of ions_________—complete transfer of 1 or more electrons from one atom to another (one loses, the other gains) forming oppositely charged ions that attract one another, producing large crystals of ions _________—some valence electrons shared between atoms… forming a molecule_________—some valence electrons shared between atoms… forming a molecule _________ – holds atoms of a metal together with “sea of electrons”_________ – holds atoms of a metal together with “sea of electrons” Most bonds are somewhere in between ionic and covalent.

4. 4 Ionic Bonds We’ve been through this in great detail already. Positive cations and the negative anions are attracted to one another (remember the Paula Abdul Principle of Chemistry: Opposites Attract!) Therefore, ionic compounds are usually between metals and nonmetals (opposite ends of the periodic table).

5. 5 Crystal Structure: Ionic Bonding

6. What are some characteristics of an ionic bond? 1.Crystalline at room temperatures 2.Have higher melting points and boiling points compared to covalent compounds 3.Conduct electrical current in molten or solution state but not in the solid state 4.Polar bonds

7. 7 What happens when atoms don’t easily gain/lose electrons? Sharing is caring! Atoms still want to follow the octet rule Covalent bonds are found in all compounds with carbon, all polyatomic ions, and many other compounds How can we share electrons? … Time for a demo.

8. 8 Chemical Bonds, Lewis Symbols, and the Octet Rule Use Lewis dot diagrams to represent valence electrons.

9. 9 Electron Distribution in Molecules Electron distribution is depicted with Lewis (electron dot) structuresElectron distribution is depicted with Lewis (electron dot) structures This is how you decide how many atoms will bond covalently! (In ionic bonds, it was decided with charges)This is how you decide how many atoms will bond covalently! (In ionic bonds, it was decided with charges) G. N. Lewis 1875 - 1946

10. 10 Shared and Lone Pairs In a covalent bond, valence electrons are distributed as SHARED (BONDING) PAIRS and unshared or LONE PAIRS.In a covalent bond, valence electrons are distributed as SHARED (BONDING) PAIRS and unshared or LONE PAIRS. HCl lone pair (LP) shared or bond pair This is called a LEWIS structure.

11. 11 Bond Formation A covalent bond results from an overlap of atomic orbitals on neighboring atoms with shared pairs of electrons. The electrons spend time in both atoms. Cl HH + Overlap of H (1s) and Cl (2p) Note that each atom has a single, unpaired electron.

12. 12 Review of Valence Electrons Remember from the electron chapter that valence electrons are the electrons in the OUTERMOST energy level… that’s why we did all those electron configurations!Remember from the electron chapter that valence electrons are the electrons in the OUTERMOST energy level… that’s why we did all those electron configurations! B is 1s 2 2s 2 2p 1 ; so the outer energy level is 2, and there are 2+1 = 3 electrons in level 2. These are the valence electrons!B is 1s 2 2s 2 2p 1 ; so the outer energy level is 2, and there are 2+1 = 3 electrons in level 2. These are the valence electrons! Br is [Ar] 4s 2 3d 10 4p 5 How many valence electrons are present?Br is [Ar] 4s 2 3d 10 4p 5 How many valence electrons are present?

13. 13 Review of Valence Electrons Number of valence electrons of a main (A) group atom = Group number Not the transition metals

14. 14 Steps for Building a Covalent Bond 1.Atoms share electrons so that each can “say” they have 8 (octet rule). 2.Place first atom in center, shared pairs around the sides. 3.A Shared pair is converted to a LINE. (single bond). 4.More than one shared pair is converted to more than one line (DOUBLE OR TRIPLE BOND) 5.You are finished when the octet rule is satisfied for each atom, and the total number of electrons is correct.

15. 15 Time for Some Examples Carbon Tetrachloride Ammonia Chlorine molecule Bromine molecule The seven diatomic elements are H, O, N, Cl, Br, I, and F

16. 16 Carbon Dioxide, CO 2 1. Central atom = 2. Valence electrons = 3. Form bonds. 4. Place lone pairs on outer atoms. This leaves 12 electrons (6 pair). 5. Check to see that all atoms have 8 electrons around it except for H, which can have 2. C 4 e- O 6 e- X 2 O’s = 12 e- Total: 16 valence electrons

17. 17 Carbon Dioxide, CO 2 6. There are too many electrons in our drawing. We must form DOUBLE BONDS between C and O. Instead of sharing only 1 pair, a double bond shares 2 pairs. So one pair is taken away from each atom and replaced with another bond. C 4 e- O 6 e- X 2 O’s = 12 e- Total: 16 valence electrons How many are in the drawing?

18. 18 Double and even triple bonds are commonly observed for C, N, P, O, and S H 2 CO SO 3 C2F4C2F4C2F4C2F4

19. 19 Now You Try One! Draw Sulfur Dioxide, SO 2

20. What are some characteristics of a covalent bond? 1. 1.Covalent bonds have definite and predictable shapes. 2. 2.Very strong 3. 3.Low melting and boiling points 4. 4.Flammable (often) 5. 5.Solid, liquid, or gas at room temp

21. Metallic Bonding What is a Metallic Bond? - A metallic bond occurs in metals. A metal consists of positive ions surrounded by a “sea” of mobile electrons. Name 4 Characteristics of a Metallic Bond. 1. 1.Good conductors of heat and electricity 2. 2.Great strength 3. 3.Malleable and Ductile 4. 4.Luster This shows what a metallic bond might look like.