1. LecturePLUS Timberlake1 Covalent Bonding

2. LecturePLUS Timberlake2 Covalent Bonds Recently we worked with IONIC COMPOUNDS which form when positive CATIONS combine with negative ANIONS. Not ALL compounds involve ions. In COVALENT BONDING, valence electrons are shared between two atoms. Electrons are NOT transferred from one atom to another, so they do not develop “+” or “-” charges as do ions. Generally form between TWO NONMETAL ELEMENTS from GROUPS 14, 15, 16, and 17 but can involve elements FROM OTHER GROUPS. Covalent compounds are also called MOLECULAR COMPOUNDS.

3. LecturePLUS Timberlake3 EXAMPLE Two Hydrogen atoms move close together to SHARE valence electrons. H  +  H H H

4. LecturePLUS Timberlake4 For example, NITROGEN and OXYGEN can form several different compounds: NO NO 2 NO 3 N 2 O N2O2N2O3 N2O4N2O5N2O2N2O3 N2O4N2O5 If we named this NITROGEN OXIDE, which one would we be talking about? The SAME TWO ATOMS can share DIFFERENT NUMBERS of electrons. There is more than one possible formula combination for the same group of atoms.

5. LecturePLUS Timberlake5 Naming Covalent (Molecular) Compounds In order to name a COVALENT compound, we follow the same basic rules as for BINARY IONIC compounds….with one added step. Since the same group of atoms can bond in different proportions, we must indicate HOW MANY OF EACH ATOM there is in the compound.

6. LecturePLUS Timberlake6 Naming Covalent Compound 1. Name the first element by its name, adding a NUMBER PREFIX ONLY IF THERE IS MORE THAN ONE ATOM. 2. Name the second element by its name, but: A. Change the ending to IDE. B. Add a NUMBER PREFIX to tell how many, even if there is only one!

7. LecturePLUS Timberlake7 Number Prefixes for Covalent Compounds 1 – Mono 2 – Di 3 – Tri 4 – Tetra 5 – Penta 6 – Hexa 7 – Hepta 8 – Octa 9 – Nona 10 –Deca

8. LecturePLUS Timberlake8 When adding prefixes, the “A” or “O” of the prefix may need to be DROPPED if the element starts with a VOWEL, such as: Hexa added to OXIDE becomes: Hexoxide NOT Hexaoxide

9. LecturePLUS Timberlake9 Practice Problems ExampleWrite the formula for: Trinitrogen Pentachloride Tri = 3 Penta = 5 nitrogen chloride = chlorine So this compound needs 3 NITROGEN and 5 CHLORINE The 3 and 5 are the SUBSCRIPTS in the formula. N 3 Cl 5

10. WRITE the formula for these Covalent Compounds: (To make it easier, prefixes are colored in these practice problems) Click HERE for a PERIODIC TABLE.HERE 1. carbon monoxide 2. carbon dioxide 3. phosphorus trichloride 4. carbon tetrachloride 5. dinitrogen monoxide LecturePLUS Timberlake10

11. LecturePLUS Timberlake11 1. CO carbon monoxide 2. CO 2 carbon dioxide 3. PCl 3 phosphorus trichloride 4. CCl 4 carbon tetrachloride 5. N 2 Odinitrogen monoxide

12. LecturePLUS Timberlake12 MORE PRACTICE PROBLEMS Write the correct formula for the following Covalent compounds. 1. triphosphorus monoxide 2. phosphorus pentoxide 3. diphosphorus pentoxide 4. dichlorine heptoxide 5. dichlorine tribromide 6. silicon tetroxide 7. carbon tribromide 8. antimony disulfide **STOP HERE**

13. Diatomic Elements Some elements, when not bonded to other elements, bond to another atom of their own kind. These are known as DIATOMIC ELEMENTS. There are 8 naturally existing diatomic elements: ALL of family 17 (Halogen Family). Oxygen, Nitrogen and Hydrogen These elements should be written as: F 2, Cl 2, Br 2, I 2, At 2, O 2, H 2, N 2 when they are NOT part of a compound.

14. LecturePLUS Timberlake14 Pure vs Polar Covalent When two atoms share an electron, the ELECTRONEGATIVITY value of each atom determines how closely the electron is pulled toward one atom or the other. Recall Electronegativity [Eneg] is the measure of the attraction one atom has for another’s valence electrons. SEE CHART NEXT SLIDE FOR Eneg Values.

15. LecturePLUS Timberlake15 Electronegativity Values

16. LecturePLUS Timberlake Determining Bond Type To determine the type bond between any two atoms, find the difference between their E neg values: 0 to 0.5 - PURE Covalent – the e- is shared at an equal distance between both atoms. 0.51 to 1.99 – POLAR Covalent – the e- is shared closer to one atom than the other…this gives the atom the e- is closest to a slightly NEGATIVE charge [delta -] and the one the e- is father away from a slightly POSITIVE charge [delta +]. 2.0 or greater – the e- is completely transferred from one atom to the other and forms an IONIC BOND.

17. Practice Problems Use Eneg values to predict the type of bond that would form between each pair of atoms: 1. Ca and Br ____________2. H and O ______________ 3. Pb and S ______________ 4. Au and S_______________ 5. Sn and I ______________6. C and H _______________ 7. B and H _______________8. Fr and F _______________ 9. N and Al _______________ LecturePLUS Timberlake17