Question

unit 5 test bonding
name
place the letter of your answer in the blank. you may circle your answer as well but only the letter in the blank will be graded

1. the electron dot structure for aluminum shows three dots spaced around the chemical symbol for aluminum (al)

what do the three dots represent?
a. the total number of electrons in the aluminum atom
b. the number of valence electrons in the aluminum atom
c. the number of protons that aluminum has in the outer shell
d. the number of neutrons in the aluminum atom

1. chlorine atoms typically gain one electron each to become chloride ions of charge 1-

in the electron dot structure, how many dots are placed around the chemical symbol for chlorine, cl?
a. 0
b. 1
c. 7
d. 8

1. what type of bond forms when one or more electrons transfer from one atom to another atom?

a. ionic
b. covalent
c. metallic
d. all of these

1. the electron configuration of phosphorus is written as ( 1 s^{2} 2 s^{2} 2 p^{6} 3 s^{2} 3 p^{3} ). how many valence electrons does phosphorus have?

a. 2
b. 3
c. 5
d. 15

1. why do ionic compounds conduct electric current when they are melted or dissolved in water only?

a. the ions readily gain or lose electrons to acquire new charges when melted or dissolved in water.
b. the ions readily gain or lose electrons to become atoms when melted or dissolved in water.
c. the ions are free to move when melted or dissolved in water.
d. none of these

1. which is a unique characteristic of the bonding between metal atoms?

a. atoms share valence electrons only with neighboring atoms to reach a stable octet.
b. electrons move among many atoms creating a sea of mobile electrons.
c. atoms must give away electrons to reach a stable octet.
d. atoms require additional electrons to reach a stable octet.

1. which of the following is the name given to the pairs of valence electrons that do not participate in bonding in molecules?

a. unshared pairs
b. inner pairs
c. outer pairs
d. unvalenced pairs

1. which of the following covalent bonds is nonpolar?

a. h-h
b. h-c
c. h-n
d. h-f

1. according to vsepr theory, molecules adjust their shapes to keep which of the following as far apart as possible?

a. mobile electrons
b. the electrons closest to the nuclei
c. pairs of valence electrons
d. inner shell electrons

1. the shape of the methane ( (mathrm{ch}_{4}) ) molecule is called

c. planar
a. pyramidal
b. bent
d. tetrahedral

1. which of the following has three unshared pairs of electrons?

a. ( mathrm{ch}_{4} )
b. ( mathrm{h}_{2} mathrm{o} )
c. ( mathrm{hcl} )
d. ( mathrm{nh}_{3} )

1. metallic bonding allows metals to have all of the following properties except

c. malleability
a. low melting point
b. ductility
d. conductivity

Explanation:

1. Electron dot structures (Lewis structures) use dots to represent valence electrons. Aluminum has 3 valence electrons, so the three dots represent the number of valence electrons.
2. Chlorine has 7 valence electrons. When it gains one electron to become an ion, it has 8 electrons (a full outer shell). But in the electron dot structure of the atom (before gaining the electron), it has 7 dots.
3. Ionic bonds form when electrons are transferred from one atom to another. Covalent bonds involve sharing electrons, and metallic bonds involve a sea of electrons among metal atoms.
4. For the electron configuration \(1s^{2}2s^{2}2p^{6}3s^{2}3p^{3}\), the valence shell is the 3rd shell (\(n = 3\)). The number of valence electrons is \(2 + 3=5\) (from \(3s^{2}\) and \(3p^{3}\)).
5. Ionic compounds conduct electricity when melted or dissolved in water because the ions are free to move (in solid - state, ions are in fixed positions in the lattice).
6. In metallic bonding, electrons move among many atoms creating a sea of mobile electrons. In covalent bonding, atoms share valence electrons, and in ionic bonding, atoms gain or lose electrons.
7. Pairs of valence electrons that do not participate in bonding in molecules are called unshared pairs (also known as lone pairs).
8. A non - polar covalent bond occurs when the two atoms sharing electrons have the same electronegativity. \(H - H\) has the same atoms (same electronegativity), while \(H - C\), \(H - N\), and \(H - F\) have different electronegativities.
9. VSEPR (Valence - Shell Electron - Pair Repulsion) theory states that molecules adjust their shapes to keep pairs of valence electrons as far apart as possible.
10. The methane (\(CH_{4}\)) molecule has a tetrahedral shape. It has 4 bonding pairs of electrons around the carbon atom.
11. In \(HCl\), the chlorine atom has 3 unshared pairs of electrons. In \(CH_{4}\), there are no unshared pairs (all 4 valence electrons of C are bonded to H). In \(H_{2}O\), O has 2 unshared pairs, and in \(NH_{3}\), N has 1 unshared pair.
12. Metallic bonding gives metals high melting points (due to the strong attraction between metal ions and the sea of electrons), ductility (ability to be drawn into wires), malleability (ability to be hammered into sheets), and conductivity.

Answer:

1. b
2. c
3. a
4. c
5. c
6. b
7. a
8. a
9. c
10. d
11. c
12. a