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Covalent Bonding

Covalent Bonding. Covalent Bonding. Molecule: neutral group of atoms that are held together by covalent bonds Covalent Bond : sharing of electrons between two atoms, “owned” by the two bonded atoms. Occurs most commonly between nonmetal elements. F. F. 8 Valence electrons.

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Covalent Bonding

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  1. Covalent Bonding

  2. Covalent Bonding • Molecule: neutral group of atoms that are held together by covalent bonds • Covalent Bond: sharing of electrons between two atoms, “owned” by the two bonded atoms. • Occurs most commonly between nonmetal elements

  3. F F 8 Valence electrons 8 Valence electrons Covalent bonding: Fluorine • Fluorine has seven valence electrons • A second Fluorine atom also has seven • By sharing electrons…Both atoms end up with full orbitals (stable octets)

  4. n = 2 Covalent Bonding: Oxygen Atoms share electrons to achieve a stable octet (8 electrons in valence shell). - - - - - - - n = 1 - - - - - - - - - - - - - - + - - - - - - - - - - - - - - - - - - - - - O2 O 1s22s22s22p4 O 1s22s22s22p4

  5. Octet Rule • The Octet Rule applies to covalent bonds: atoms bond to achieve 8 valence electrons • Exceptions: • Hydrogen is satisfied with 2 valence electrons • Beryllium is content with 4 valence electrons • Boron is satisfied with 6 valence electrons

  6. Bond Strength • The strength of a bond is determined by how many electrons are shared between two atoms. • Single Bond - Atoms share one PAIR of electrons (2 e-) • Weakest bond, most flexible • Double Bond – Atoms share TWO pairs (4 e-)of electrons • Triple Bond – Atoms share THREE pairs (6 e-)of electrons • Strongest bond, most rigid

  7. (Pg. 182)Relationship between Bond Length and Bond Energies • Bond Energy = Energy required to break a chemical bond • Unit: kJ • High bond energy = High bond strength Plot Bond length on the x-axis, Plot bond energy on the y-axis • Result: Bond length decreases as the strength of the bond _____________. • Answer: Increases

  8. x x x F x x x x x x x x F C F x x x x x x x x F x x x x x Covalent Bonds: Lewis Structures • Lewis Structure: It shows the molecular arrangement of covalent molecules, using the electron-dot notation. • Lone Pair electrons = Unpaired electrons Q: Do we use lewis structures to illustrate ionic bonds?

  9. How To: Lewis Structures (Ex: CH3I) Step 1. Determine the type and number of atoms in the molecule. Step 2. Determine the total number of valence electrons available in the molecule. Step 3. Arrange the atoms. Q: Which atom is central? *(next slide) Step 4. Start by putting two electrons between atoms for each covalent bond. Then place electrons around each atom to fulfill the Octet Rule Step 5. Count the electrons to check your work. Ask yourself, does it equal the number of electrons in step 2?

  10. How to: Lewis Structures Q: Which atom is central? A: If carbon is present, it is the central atom. Hydrogen is never the central atom. Otherwise, the central atom is the least-electronegative atom. Q: What does “electronegative” mean? A: Electronegativity: The ability of an atom to attract electrons in a chemical compound. If an atom is highly electronegative, it is the more “dominant” atom and “hogs the electrons.”

  11. H x x H H x H x x H H x x x x o o x I N I x H C H x x x x x x o o x x o o x I x o N x I o N H x x o x x o x x o x x o x x x x x x x x x x x O x x O x x O x O = C = O x x x x x x x x o x I x x x x x x x o o o o C x I x x o o o C C C o x x x o o o o x x o o o x x I x x x x x Lewis Structure methane (CH4) nitrogen triiodide (NI3) carbon dioxide (CO2)

  12. Lewis Structures: Practice • Ammonia, NH3 • Hydrogen Sulfide, H2S • Silane, SiH4 • Phosphorus Trifluoride, PF3

  13. Naming Covalent Molecules • Greek prefixes are used to indicate how many atoms of each element are present in the molecule. P4O10 Prefix needed if first element contributes more than one atom RootName of 2nd element + ide Prefix indicating number of atoms Name of first element + + tetraphosphorus decoxide

  14. Naming Covalent Molecules • The “o” or “a” at the end of a prefix is usually dropped when another vowel follows it. • “monooxide” becomes “monoxide” • “pentaoxide” becomes “pentoxide”

  15. Examples…Name the following - • SO3: Sulfur ______?________ • Answer: Sulfur trioxide • PBr5: _____?_____ _______?________ • Answer: Phosphorus pentabromide • As2O5: ______?_____ Pentoxide • Answer: Diarsenic Pentoxide

  16. Examples… Write the chemical formulas - • Carbon tetriodide • Answer: CI4 • Dinitrogen trioxide • Answer: N2O3 • Silicon dioxide • Answer: SiO2

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