CHEM 35
Introductory Chemistry
Quiz #2
September 15, 2000
Name: Anne Serkey
1. How do isotopes of a particular element differ in their sub-atomic
composition (i.e., # of protons, neutrons, and electrons)?
Isotopes of a particular element have the same number of
protons and electrons, but differ in the number of
neutrons – hence, their atomic masses differ.
2. Briefly explain why ionic bonds are formed when metals and non-metals
react and why covalent bonds are formed when non-metals react with
each other. Please use the concepts of Ionization Energy (IE), Electron
Affinity (EA), and/or Electronegativity (EN) in your answer.
Metals have lower IE’s than non-metals, while non-metals
have a greater EA than do metals. This means that metals
prefer to give up an electron (becoming a cation) while
non-metals would prefer to pickup electrons (becoming an
anion). This is quantified with EN values which relate to
the ability of an element to attract electrons when
bonded to another element. Non-metals have much larger
EN’s than do metals, so when they bond, they attract much
most of the electron density from the metal, making an
ionic bond. When non-metals bond together, they have very
similar EN’s and so the electron density is more equally
shared, forming a covalent bond.
3. Using Lewis dot diagrams and VSEPR theory, predict the shape of CO2. Is
there a dipole moment associated with this molecule (assume that the
electronegativities of C and O are different)? Explain
4 + 12 = 16 electrons, total
_ _
|O = C = O| LINEAR
4 double bonds + 4 nonbonded pairs = 16 electrons
Although each C=O bond has a dipole moment, they are
symmetrically opposed, so there is no net dipole
moment for CO2.
