Covalent Compounds!

1. Covalent Compounds! Chapter 6 Pgs. 188 - 221

2. Covalent Bond A bond formed when atoms share one or more pairs of electrons. Recall: it is a bond between nonmetals • Nonmetals hold onto their valence electrons. • Why?? • Because of their high electronegativity! They can’t transfer valence electrons to bond, they attract other electrons to themselves. • Still want noble gas configuration (Octet Rule), and they BOTH can’t gain! • Get it by sharing valence electrons with each other.

3. n = 2 - - - - Covalent Bond - - - - n = 1 - - - - - - - - + - - - - - - - - - - - - O [He]2s22p4 O [He]2s22p4 O2 Sharing of electrons to achieve a stable octet (8 electrons in valence shell).

4. Molecular Orbital • When shared electrons move in the space surrounding the nuclei of 2 atoms, the space these shared electrons move within is called a molecular orbital • Makes covalent bonds stronger than ionic • The orbital which is formed by the overlap of adjacent atomic orbitals • Ex: H2

5. Bond Length • The distance between two bonded atoms at their minimum potential energy; the average distance between the nuclei of two bonded atoms • Determined by potential energy

6. Potential Energy of Covalent Bonds • Recall: potential energy is energy of position (close vs far apart) • Unbonded atoms (far apart) tend to have high potential energy (except for noble gases) • Potential energy determines bond length • Two atoms form a covalent bond at a distance where attractive and repulsive forces balance. At that distance, potential energy is at a minimum.

7. Analogy: a spring!

8. Bond Energy • The energy required to break a bond between two atoms It takes energy to break a bond and energy is released when a bond is formed

9. Bond Length and Bond Energy • In general, shorter bonds are stronger than longer bonds (require more energy to break) • In general, multiple bonds are stronger and shorter than single bonds (require more energy to break)

10. Properties of Covalent Compounds • Typically gases, liquids, or solids with low melting points • Most covalent compounds are insoluble in water • If they do dissolve in water, the solutions typically do not conduct electricity

11. Writing Formulas of Covalent Compounds • Covalent Compounds contain two types of nonmetals Key: FORGET CHARGES What to do: Use Greek prefixes to indicate how many atoms of each element, but don’t use “mono” on first element. 1 – mono 6 – hexa 2 – di 7 – hepta 3 – tri 8 – octa 4 – tetra 9 – nona 5 – penta 10 – deca

12. Binary Covalent Compounds Containing Two Nonmetals • Name the less electronegative element first with the Greek prefix indicating the number of atoms of that element present. • Name the more electronegative non-metal with the Greek prefix indicating the number of atoms of that element present. a. Ending should be replaced by the suffix –ide. Greek prefixes you should know: Mono Di Tri Tetra Penta Hexa Hepta Octa Nona Deca 1 2 3 4 5 6 7 8 9 10

13. H 2.1 Li 1.0 Be 1.5 B 2.0 C 2.5 N 3.0 O 3.5 F 4.0 Na 0.9 Mg 1.2 Al 1.5 Si 1.8 P 2.1 S 2.5 Cl 3.0 K 0.8 Ca 1.0 Sc 1.3 Ti 1.5 V 1.6 Cr 1.6 Mn 1.5 Fe 1.8 Co 1.8 Ni 1.8 Cu 1.9 Zn 1.7 Ga 1.6 Ge 1.8 As 2.0 Se 2.4 Br 2.8 Rb 0.8 Sr 1.0 Y 1.2 Zr 1.4 Nb 1.6 Mo 1.8 Tc 1.9 Ru 2.2 Rh 2.2 Pd 2.2 Ag 1.9 Cd 1.7 In 1.7 Sn 1.8 Sb 1.9 Te 2.1 I 2.5 * Cs 0.7 Ba 0.9 La 1.1 Hf 1.3 Ta 1.5 W 1.7 Re 1.9 Os 2.2 Ir 2.2 Pt 2.2 Au 2.4 Hg 1.9 Tl 1.8 Pb 1.8 Bi 1.9 Po 2.0 At 2.2 y Fr 0.7 Ra 0.9 Ac 1.1 * Lanthanides: 1.1 - 1.3 y Actinides: 1.3 - 1.5 Below 1.0 2.0 - 2.4 1.0 - 1.4 2.5 - 2.9 1.5 - 1.9 3.0 - 4.0 Electronegativities 1A 8A 1 1 3A 5A 7A 2A 4A 6A 2 2 3 3 2B 4B 6B 8B 1B 3B 5B 7B Period 4 4 5 5 6 6 7 Hill, Petrucci, General Chemistry An Integrated Approach 2nd Edition, page 373

14. Naming Covalent Compounds

15. Binary Covalent CompoundsContaining Two Nonmetals N2O dinitrogen monoxide N2O3dinitrogen trioxide N2O5dinitrogen pentoxide ICl iodine monochloride ICl3 iodine trichloride SO2 sulfur dioxide SO3 sulfur trioxide

16. Naming Covalent Compounds • ClO2 • P4S5 • SeF6 • O2 Chlorine Dioxide TetraphosphorusPentasulfide Selenium hexafluoride Oxygen (diatomic molecule)

17. Writing Formulas Nitrogen Trifluoride Phosphorus Triiodide DinitrogenTrioxide Ammonia (TrihydrogenMononitride) NF3 PI3 N2O3 NH3

18. Binary Covalent CompoundsContaining Two Nonmetals As2S3 • ________________ diarsenic trisulfide • ________________ sulfur dioxide • P2O5 ____________________ • ________________ carbon dioxide • N2O5 ____________________ • H2O ____________________ SO2 diphosphorus pentoxide CO2 dinitrogen pentoxide dihydrogen monoxide

19. Writing Formulas of Covalent Compounds EXAMPLES: carbon dioxide CO dinitrogen trioxide N2O5 carbon tetrachloride NI3 CO2 carbon monoxide N2O3 dinitrogen pentoxide CCl4 nitrogen triiodide

20. Please practice using the Formulas/Naming Covalent Compounds Worksheet

21. Bond Polarity • The polarity of a bond depends on the electronegativities of the atoms involved • The greater the difference in electronegativity, the more polar the bond

22. Nonpolar Covalent Bond • A covalent bond in which the bonding electrons are equally attracted to both bonded atoms • Electronegativity difference 0-0.5

23. Polar Covalent Bond • A covalent bond in which a shared pair of electrons is held more closely by one of the atoms • Electronegativity difference 0.5-2.1

24. Dipole • A molecule or part of a molecule that contains both positively and negatively charged regions • Can be shown in one of two ways

25. Ionic Bond • A compound in which electrons are completely transferred from one atom to another in the bond • Electronegativity difference 2.1 and up