Chemistry 100. Assignment # 6. Chemical Bonding

Transcription

1 hemistry 100 Assignment # 6 hemical Bonding 1. heck the true statements: a. Metals tend to lose valence electrons whereas non-metals tend to gain electrons. True b. K is a non-metal and is a metal. alse c. Lithium bromide is a molecular compound. alse d. A pair of electrons being shared between two atoms can be represented as a double line. alse e. 2 molecule has two double bonds. True f. Since is more electronegative than, the - bond is less than - bond. alse g. - bond is more than B- bond. alse 2. Write the electron dot formula for the following atoms: a, K,, e, e,, S, Si, Element Electron Dot Structure Element Electron Dot Structure a a K K S S Si Si e e e e 3. Write the electron dot formula for the following compounds: a,, 2, a, MgBr 2, Li 2, 2, 2, 2

2 ompound Electron Dot ormula ompound Electron Dot ormula a Li a 2 2- Li Li 2 2 a 2-2 a 2+ 2 MgBr 2 Mg 2+ Br Br 4. a. What is meant by the term electronegativity? Electronegativity of an atom is the attractive force the atom exerts on a shared pair of electrons. b. ow does bond ity depend on the electronegativity scale? The greater the difference in electronegativities between the two atoms, the higher the ity of the bond. When the electronegativity difference is large, ionic bonds form. c. Arrange the following atoms in order of increasing electronegativities (lowest first): K,, Br, B, Al Electronegativity increases as we go up a group and as we go from left to right across the periodic table. Answer: K < Al < B < Br < d. Arrange the following atoms according to their electronegativities (highest first): P,,, Rb, a Answer: > > P > a > Rb

3 5. or each pair of bonds, determine which one is more : The answer is in bold a. - or -Br b. - or - c. P- or P- d. Si- or Si- 6. Which of the following compounds do you expect to be ionic: Generally, when metals react with non-metals, they produce ionic compounds. The answer is in bold. Mg 2,, ai, a, a 2, a 2 S, 2, 4, Rb, Ba 2, 2 7. Predict the geometry of each molecule, and then determine which ones are : irst, draw the electron dot formula of the molecular compound, then using the electron pair geometry around the central atom predict the geometry of the molecule. Use the geometry of the molecule to then predict its ity. 2 ( is the central atom) non ( is the central atom) 2 2 non Al 3 (this a molecular compound even though it includes a metal, Al, and a nonmetal,. Also, notice that the central atom has an incomplete octet) Al trigonal planar non

4 4 tetrahedral non 3 trigonal pyramidal 2 bent (v-shaped) S 2 S bent (v-shaped) P 3 P trigonal pyramidal 3 (there is a single covalent bond between carbon and oxygen) tetrahedral about the atom S 2 ( is the central atom) S S non Br Br

5 S 2 (S is the central atom) This one is more challenging compared to the rest of the structures. There is also the question of charges on the atoms within the structure. These have been ignored. You will learn how to assign these charges in your next chemistry course. S bent (v-shaped) 2 2 tetrahedral 8. Write structural formulas showing the geometry of each compound below. Indicate which ones are. 2, P 3, 2, 2,, 3, 3, 2 2, bent (v-shaped) P 3 P trigonal pyramidal 2 trigonal planar

6 2 non bent (v-shaped) 3 trigonal pyramidal 3 tetrahedral 2 2 bent about the atom 2 4 trigonal planar about each atom non 9. What is wrong with each of the chemical formulas below: e 2, Li, KS, Al 2

7 e 2 this is inconsistent with bonding rules. The elium atom already has a stable arrangement of electrons (a filled s subshell). If a bond was to be made between the two helium atoms, then an unstable arrangement of electrons is produced as each atom will have to accommodate four electrons in its valence shell. Li this is inconsistent with bonding rules. Each lithium atom loses one electron to achieve a stable electron arrangement (a stable octet), while the oxygen atom must gain two electrons to achieve a stable octet. ence, for each oxygen ion (has two negative charges), two lithium ions (each has one positive charge) are required to make lithium oxide, Li 2. KS this is inconsistent with bonding rules. Each potassium atom loses one electron to achieve a stable electron arrangement (a stable octet), while the sulfur atom must gain two electrons to achieve a stable octet. ence, for each sulfur ion (has two negative charges), two potassium ions (each has one positive charge) are required to make potassium sulfide K 2 S. Al 2 this is inconsistent with bonding rules. Each aluminum atom loses three electrons to achieve a stable electron arrangement (a stable octet), while each oxygen atom must gain two electrons to achieve a stable octet. ence in order to balance the charges, for each two aluminum ions (each has three positive charges), three oxygen ions (each has two negative charges) are required to make aluminum oxide, Al a. Draw the electron dot formula for the compound silicon dioxide, Si 2. Si b. riticize the following statement: Since oxygen is more electronegative than silicon, silicon dioxide is a molecule. The ity of a molecule is determined by its geometry. The molecule can have bonds, but due to symmetrical distribution of bonds about a central atom the forces may cancel out. In this case, oxygen is more electronegative than silicon and the siliconoxygen bond is. owever, due to the symmetry of the molecule, bond ities cancel out and the molecule is non.