Chemistry Reference
In-Depth Information
12. [B. ethene]—If you try to sketch the structural formula for C
2
H
4
, you will
see that you will need a double bond between the two carbon atoms, in
order to occupy all of the bonding electrons. We use the prefix “eth”
because each molecule has two carbon atoms, and the suffix “ene” because
it contains a double bond.
13. [A. C
2
H
2
]—An alkyne must contain a triple bond. If you draw structural
formulas for each of the answer choices, only choice A will have a triple
bond. Alkynes also have the general formula of C
n
H
2n-2
. Only answer choice
A follows that formula.
14. [B. MgF
2
]—We look for an electronegativity difference of greater than 1.7,
and we find that in answer B only. Magnesium has an electronegativity of
1.2 and fluorine has an electronegativity of 4.0, making the difference 2.8.
Notice that these two elements are on the opposite sides of the periodic
table.
15. [C. NaNO
3
]—To answer this question correctly, we look for a compound
that contains a polyatomic ion. Sodium nitrate (NaNO
3
) contains the
nitrate (NO
3
-
) ion, which is held together by covalent bonds. The
polyatomic ion then attaches to the sodium ion with an ionic bond.
16. [D. H
2
O
(s)
]—A molecular compound must contain two elements (which
rules out answer choice A) with similar electronegativities. Often, you can
just look for the compound that contains no metals, and be correct.
17. [B. H
2
O]—Carbon dioxide and diatomic nitrogen have a linear shape.
Methane has a tetrahedral shape. Water is the classic example of a bent
shape.
18. [A. NH
3
]—Although all four answer choices represent molecular
substances, only the ammonia molecule is asymmetrical.
19. [D. Cl
-
]—Of course, a polyatomic ion must contain more than one atom.
The chloride ion does not.
20. [B. CBr
4
]—The molecules with a tetrahedral shape follow the basic formula
XY
4
.
