Covalent bonding occurs in nonmetal compounds. Use the highlighter to select the compounds that are covalently bonded. 2 C 2 Cl Li NaF Mg C 4 N NaCl 3 Drag this to the target to reveal the answers. Properties of Covalent Bonds: generally soft irregular shape/no rigid structure *except when network solids Do not conduct. Ever. usually insoluble (when non polar) low melting/boiling points Bonding between non metals only shared valence e form bond Covalent Bonds always share e in PAIRS. Each atom wants a stable octet. Shared e count for both atoms 1
Electronegativity Difference Ionic vs Covalent Covalent Bonds 0 0.4 1.7 4.0 Polar Covalent Bond Ionic Bonds Nonpolar Covalent Bond Ionic Character Polarity Non polar covalent bonds Electro neg difference of Share e equally (even distribution) Atoms in a covalent bond are held together by electrostatic forces of attraction between positively charged nuclei and negatively charged shared electrons. Analogy: Examples: Br Br Br Br : Note! Dashes represent 2 shared e 3 D Molecular Models 2
Polar Covalent Bonds: Electroneg difference of Share e unequally Atom with a higher electroneg value: Atom with a lower electroneg value: Analogy: e.g. I F :F Slightly negative Slightly positive F I:F 3 D Molecular Models Multiple Covalent Bonds: 2 atoms can share more than one pair of electrons N 2 2 N N N N Triple Covalent Bond = Double Covalent Bond 3
Covalent Molecules Looks at ENTIRE Molecule e distribution ** Symmetrical vs. Asymmetrical ow is this different than bond polarity? Bond vs. Molecule Analogy: Non polar MLECULES e distributed (spread out) evenly Diatomics: Bond: Molecule: Atoms with polar bonds can form non polar molecules: e.g. C 2 Methane 3 D molecule :=C=: 4
Polar Molecules uneven electron distribution dipole: look for sides that do not match http://www.edinformatics.com/interactive_molecules/water.htm Classify the Following MLECULES and SAPES pyramidal linear tetrahedral tetrahedral bent planar tetrahedral 3 D Virtual Images 5
C Cl C C Rules for Drawing: 1) Count the total valence electrons for the molecule: To do this, find the number of valence electrons for each atom in the molecule, and add them up. 2) Figure out how many octet electrons the molecule should have, using the octet rule: The octet rule tells us that all atoms want eight valence electrons (except for hydrogen, which wants only two), so they can be like th nearest noble gas. Use the octet rule to figure out how many electrons each atom in the molecule should have, and add them up. The only weird element is boron it wants six electrons. 3) Subtract the valence electrons from octet electrons: r, in other words, subtract the number you found in #1 above from the number you found in #2 above. The answer you get will be equal to the number of bonding electrons in the molecule. 4) Divide the number of bonding electrons by two: Remember, because every bond has two electrons, the number of bonds in the molecule will be equal to the number of bonding electrons divided by two. 5) Draw an arrangement of the atoms for the molecule that contains the number of bonds you found in # 4 above: Some handy rules to remember are these: ydrogen and the halogens bond once. The family oxygen is in bonds twice. The family nitrogen is in bonds three times. So does boron. The family carbon is in bonds four times. A good thing to do is to bond all the atoms together by single bonds, and then add the multiple bonds until the rules above are followed. 6) Find the number of lone pair (nonbonding) electrons by subtracting the bonding electrons (#3 above) from the valence electrons (#1 above). Arrange these around the atoms until all of them satisfy the octet rule: Remember, ALL elements EXCEPT hydrogen want eight electrons around them, total. ydrogen only wants two electrons. 6
Let's do an example: C 2 Note: Each of the numbers below correspond to the same numbered step above. 1) The number of valence electrons is 16. (Carbon has four electrons, and each of the oxygens have six, for a total 4 + 12 = 16 electrons). 2) The number of octet electrons is equal to 24. (Carbon wants eight electrons, and each of the oxygens want eigh electrons, for a total of 8+16 = 24 electrons). 3) The number of bonding electrons is equal to the octet electrons minus the valence electrons, or 8. 4) The number of bonds is equal to the number of bonding electrons divided by two, because there are two electro per bond. As a result, in C2, the number of bonds is equal to 4. (Because 8/2 is 4). 5) If we arrange the molecule so that the atoms are held together by four bonds, we find that the only way to do it so that we get the following pattern: =C=, where carbon is double bonded to both oxygen atoms. 6) The number of nonbonding electrons is equal to the number of valence electrons (from #1) minus the number of bonding electrons (from #3), which in our case equals 16 8, or 8. Looking at our structure, we see that carbon already has eight electrons around it. Each oxygen, though, only has four electrons around it. To complete the picture, each oxygen needs to have two sets of nonbonding electrons, as in this Lewis structure: 7