Chemistry- Chapter 3 Test

Use your answers to #6 to help answer the following questions. How many sodium atoms are likely to bond with chlorine? How many sodium atoms are likely to bond with sulfur? Can aluminum and chlorine combine in an ionic bond? If yes, how many of each ion would be needed? If no, why not? Can aluminum and sodium combine in an ionic bond? If yes, how many of each ion would be needed? If no, why not?

a. 1 sodium atom will bond with each chlorine atom (1:1 ratio) b. Two sodium atoms will bond with each sulfur atom (2:1 ratio) c. Yes, since one is a cation and one is an anion. There will be 3 chlorine ions for each aluminum ion (1:3 ratio) d. No, since both sodium and aluminum form cations, they will not bond together. For an ionic bond, you must have at least 1 cation and at least 1 anion.

The following structure represents an organic hydrocarbon. How many sigma bonds are present in the molecule? How many pi bonds are present?

10 sigma bonds, 3 pi bonds

For each pair of atoms listed below, state what type of bonding is most likely to occur between the atoms (ionic, polar covalent, or non-polar covalent). a. Boron and chlorine b. Cobalt and fluorine c. Carbon and sulfur

A. Polar covalent bond b. Ionic bond c. nonpolar covalent bond

Of the following isoelectronic series, which particle will have the smallest radius? Why? K+, Ca2+, S2-, Cl-, Ar

Ca2+ will have the smallest radius. All of the particles listed contain 18 electrons. But Ca2+ has the most protons (20) and therefore the greatest amount of attraction between the nucleus and electrons, pulling the electrons in the closest.

Explain why Cl1- ions have a larger radius than Cl atoms.

Chlorine anions are larger than chlorine atoms because the ion has more electrons than protons. This makes it more difficult for the protons to attract the electrons, even though there is the same number of electron shells. This weaker attraction makes the ion larger. There are also more electron-electron repulsions causing the electrons to spread out within the existing orbitals.

Is energy released or absorbed when a chemical bond is made? Is energy released or absorbed when a chemical bond is broken?

Energy is released when a bond is formed (atoms go from having a lot of energy, to having less, that extra energy is released in some form). When a bond is broken, and the atoms return to higher energy status, energy is absorbed.

Describe the difference between polar and nonpolar covalent bonds. How can you tell whether a bond is polar or nonpolar?

In a nonpolar covalent bond, electrons are shared equally, while in a polar covalent bond, electrons are shared unequally.

Describe the difference between polar and nonpolar molecules. How can you tell whether a molecule is polar or nonpolar?

In a polar molecule, the overall charge on the molecule is not distributed symmetrically. Typically these molecules have a lone pair on the central atom or are non symmetrical. Nonpolar molecules have the overall charge distributed symmetrically. These molecules do not have lone pairs on the central atom and are symmetrical.

How are ionic and covalent bonds similar? How are they different?

Ionic bonds and covalent bonds are similar in that they are both types of bonds that hold atoms together. They both allow atoms to achieve an octet and become more stable. They also both involve electrostatic attractions between positive and negative things. They are different in that ionic compounds usually involve one metal and one nonmetal while covalent compounds are usually 2 or more nonmetals. Also, ionic bonding involves the transfer of electrons and the formation of ions while covalent involves neutral atoms sharing electrons.

Why is it incorrect to say that ionic bonds form molecules?

Ionic bonds do not form molecules, which are small groups of atoms bonded together. Instead, a large number of ions are arranged in an extended crystal.

Explain why Na1+ ions have a smaller radius than Na atoms.

Sodium cations are smaller than sodium atoms because the ion has one less electron shell than the atom. Plus, the protons now outnumber the electrons and exert a stronger force of attraction on the electrons.

What is the relationship between an atom's potential energy and its stability?

The LOWER an atom's potential energy, the more stable it is. Usually, bonded atoms have lower potential energy, and are therefore more stable, than unbonded atoms.

What is meant by the term "octet rule?"? How do ionic bonds satisfy the octet rule? How do covalent bonds satisfy the octet rule?

The octet rule refers to the fact that atoms with 8 valence electrons are particularly stable. Some atoms, like the noble gasses, already have 8 valence electrons. Other atoms undergo bonding in order to achieve an octet. Ionic compounds achieve an octet by transferring electrons (one atom gains electrons while another atom loses electrons). Covalent compounds achieve an octet by sharing electrons.

How do the allotropes of carbon (graphite vs diamond) differ? How are they similar?

They differ in the bonding and arrangement of the atoms, leading to different chemical and physical properties (for example diamond is very hard while graphite is very soft). However, they both are made up entirely of carbon atoms. They are 2 different physical forms of the same element.

Explain why ionic compounds exhibit each of the following properties. Brittle High melting point Insulating as solids, but conducting as liquids/aqueous solutions.

a. Ionic compounds have high melting points because ionic bonds are fairly strong, and to melt an ionic crystal, you must break all of the bonds in the crystal. This adds up to quite a large amount of energy needed. B. Ionic compounds are hard but brittle. If the layers of ions are shifted around, you might end up with 2 cations next to each other, or 2 anions next to each other. These like-charged ions would repel each other instead of attract and cause the crystal to shatter. c. Ionic compounds are insulating as solids because, even though they have charged particles, the ions are stuck in place and cannot move around. Once the crystal is melted or dissolved, however, the compound is now a conductor because the charged ions are free to move and carry an electrical current.

Draw Lewis structures for the molecules below. Predict their molecular geometry using VSEPR theory. Then identify whether the molecules are polar or nonpolar. Finally, identify the hybridization around each central atom. a. NBr3 b. HCN c. COCl2 d. OF2

a. Pyramidal, polar, sp3 hybridized b. Linear, polar, sp c. Trigonal, polar, sp2 d. Bent, polar, sp3

Based on their number of valence electrons, decide whether each atom listed below is more likely to gain or lose electrons. Then state how many electrons it will gain or lose and the charge of the ion it will form. Finally, draw the electron dot diagram to represent the ion. a.Sodium b. Sulfur c. Chlorine d. Aluminum

a. Sodium has 1 valence electron. It will lose this 1 electron and form a Na1+ ion b. Sulfur has 6 valence electrons. It will gain 2 more electrons and form a S2- ion. c. Chlorine has 7 valence electrons. It will gain 1 more electron and form a Cl1- ion. d. Aluminum has 3 valence electrons. It will lose all 3 of its electrons and form an Al3+ ion. (All dot diagrams should include brackets and the ion charge to the upper right of the closed bracket. Sodium and aluminum should have no dots while sulfur and chlorine should have 8 dots)

Which combination of ions would you expect to have the smallest lattice energy? Why? a. Na+ and O2- b. Na+ and Cl- c. Na+ and F-

b. Na+ and Cl-. Of the three anions, the chlorine ion has a smaller charge magnitude than oxygen and is larger than both the oxygen and fluorine ions. Both of these factors decrease the force of attraction between the anion and sodium cation, resulting in a lower lattice energy.