Chapter 2

14. How many carbon atoms are in 18 molecules of benzene, C₆H₆?

108 ATOMS (6 x 18) One molecule contains 6 carbon atoms. Multiply that by 18, the number of molecules, to find the number of carbon atoms.

10. What is the mass number of tin-115?

115 Isotopes can be written as "element-mass number".

30. Determine the number of protons (p) and electrons (e) in Mg²⁺.

12 PROTONS, 10 ELECTRONS Mg has an atomic number of 12, so it contains 12 protons. The neutral atom would have 12 electrons, but because the ion has a +2 charge, this indicates that there are two fewer electrons.

15. How many oxygen atoms are in 25 molecules of sucrose, C₁₂H₂₂O₁₁ ?

275 ATOMS (25 x 11) One molecule contains 11 oxygen atoms. Multiply that by 25, the number of molecules, to find the number of oxygen atoms.

25. Based on the positions of the following elements on the periodic table, which of them would you expect to form a 3+ cation?

ALUMINUM & SCANDIUM Scandium loses one 3d electron and two 4s electrons to form the Sc³⁺ cation. Aluminum loses one 3p electron and two 3s electrons to form the Al³⁺ cation.

FORMULA: AlPO₄

ALUMNIUM PHOSPHATE

FORMULA: Al₂S₃

ALUMNIUM SULFIDE

37. Predict the chemical formula for the ionic compound formed by the elements Ag and O.

Ag₂O

35. Predict the chemical formula for the ionic compound formed by Al³⁺ and C₂H₃O₂⁻.

Al(C₂H₃O₂)₃

FORMULA: BaCr₂O₇

BARIUM DICHROMATE

22. Which of the following is an alkaline earth metal?

BERYLLIUM The alkaline earth metals are found in Group 2 and include Be, Mg, Ca, Sr, Ba, and Ra.

FORMULA: N₂O₄

DINITROGEN TETROXIDE

FORMULA: LiOH

LITHIUM HYDROXIDE

FORMULA: HClO₄(aq)

PERCHLORIC ACID

FORMULA: KF · 2H₂O

POTASSIUM FLOURIDE DIHYDRATE

11. Which of the following statements about subatomic particles are false?

The atomic number is equal to the number of neutrons in the nucleus of an atom (CORRECT: protons). Electrons are more massive than protons (CORRECT: protons are).

FORMULA: BrO⁻

HYPOBROMITE ION

48. What is the correct IUPAC name for Pb(ClO₂)₂?

lead(II) chlorite

FORMULA: K₂O

POTASSIUM OXIDE

8. What is the mass number for an atom of barium containing 56 protons and 80 neutrons?

136 (80 + 56) Mass number is protons + neutrons.

7. How many neutrons are in an atom of uranium-235?

143 (235 - 92) Uranium-235 has a mass of 235. Uranium always has 92 protons. Therefore, uranium-235 has 143 neutrons.

31. How many protons (p) and electrons (e) are found in a Se²⁻ ion?

34 PROTON, 36 NEUTRONS Se has an atomic number of 34, so it contains 34 protons. The neutral atom would have 34 electrons, but because the ion has a -2 charge, this indicates that there are two additional electrons.

FORMULA: HClO₃

CHLORIC ACID

13. Glucose is an important biological molecule with the molecular formula C₆H₁₂O₆. What is its empirical formula?

CH₂O An empirical formula shows the ratio of each element to one another in the formula. The chemical formula reduces to CH₂O.

63. Write the chemical formula for calcium chloride.

CaCl₂

65. Write the chemical formula for boric acid.

H₃BO₃

27. Classify the following compounds as ionic or covalent: KCl, CrCl₃, Cl₂O.

Ionic, ionic, covalent. Ionic bonds occur between a metal and a nonmetal. Covalent bonds occur between two nonmetals.

32. What is the formula for an ionic compound containing Mg²⁺ ions and N³⁻ ions?

Mg₃N₂ Three magnesium ions are needed to balance out the negative charge on the two nitrogen ions. This is the lowest number of each ion to reach a neutral formula unit.

19. The element symbol for nickel is:

Ni

FORMULA: Ag₂S

SILVER SULFIDE

3. The atomic mass of germanium (Ge) on the periodic table is 72.630 amu. Which of the following best explains why the atomic mass is a fraction between 72 and 73?

THE PRESENCE OF DIFFERENT ISOTOPES The atomic mass is an average that represents the abundance of each isotope.

47. What is the correct IUPAC name for CuNO₃?

copper(I) nitrate

56. What is the correct IUPAC name for CuSO₄ · 5H₂O?

copper(II) sulfate pentahydrate

43. What is the correct IUPAC name for Fe₃P₂?

iron(II) phosphide

49. What is the correct IUPAC name for Ni(IO₄)₂?

nickel(II) periodate

9. What is the mass number for an atom of nickel containing 28 protons and 32 neutrons?

60 (32 + 28) Mass number is protons + neutrons.

12. What is the atomic number for an element whose mass number is 145, which contains 84 neutrons per atom?

61 (145 - 84 = 61)

FORMULA: NH₄OH

AMMONIUM HYDROXIDE

26. An atom has nine protons and ten electrons. This makes it:

AN ION A neutral atom has an equal number of protons and electrons. If there are more or less of one than the other, the atom is an ion.

1. Which postulate(s) of Dalton's atomic theory of matter is/are NOT true?

ATOMS OF A GIVEN ELEMENT ARE IDENTICAL & ATOMS ARE INDESTRUCTIBLE.

16. Write the empirical formula corresponding to Al₂Br₆.

AlBr₃

21. Which element has the symbol Br?

BROMINE

FORMULA: CaSO₄ • 2H₂O

CALCIUM SULFATE DIHYDRATE

FORMULA: CO₃²⁻

CARBONATE ION

28. Classify the following compounds as ionic or covalent: OF₂, CuO, SeO₂.

Covalent, ionic, covalent. Ionic bonds occur between a metal and a nonmetal. Covalent bonds occur between two nonmetals.

33. What is the formula of the ionic compound containing Cu²⁺ and Cl⁻ ions?

CuCl₂ Because all compounds are neutral and the Cu²⁺ ion has twice the charge of the Cl⁻ ion, the formula of copper(II) chloride is CuCl₂.

36. Predict the chemical formula for the ionic compound formed by Cu²⁺ and P³⁻.

Cu₃P₂

17. Write the empirical formula corresponding to C₄H₈O₂.

C₂H₄O

FORMULA: S₂F₈

DISULFUR OCTAFLOURIDE

18. Columns on the periodic table are known as:

GROUPS

FORMULA: HCl

HYDROCHLORIC ACID

38. Predict the chemical formula for the ionic compound formed by the elements Li and H.

LiH

29. Which of the following is most likely to form a +2 ion?

Mg Elements in Group 2 tend to form a +2 ion by losing its two valence electrons.

24. Which of the following sets of elements and symbols is paired correctly?

NEODYMIUM, Nd

FORMULA: H₃PO₄(aq)

PHOSPHORIC ACID

6. Which subatomic particle is found in the nucleus and has a positive charge?

PROTON

4. The nucleus of an atom contains:

PROTONS & NEUTRONS

23. Which of the following is a main group element?

The main group elements are elements that belong to the s and p blocks of the periodic table (groups 1-2, 13-18).

51. What is the correct IUPAC name for Ca(CN)₂?

calcium cyanide

42. What is the correct IUPAC name for CrCl₂?

chromium(II) chloride

46. What is the correct IUPAC name for Fe(NO₂)₂?

iron(II) nitrite

2. A mass spectrometer measures neon to have two masses: 20 and 22 atomic mass units. These are:

ISOTOPES Isotopes are forms of the same element that differ in the number of neutrons but contain the same number of protons. This yields atoms of the same element that have different masses.

5. Which element was originally named argentum?

SILVER (explains "Ag")

FORMULA: Na₂SO₃

SODIUM SULFATE

20. Of the following compounds, which contains a metalloid?

SiF₄ Metalloids are elements that have properties of both metals and nonmetals. The metalloids are: B, Si, Ge, As, Sb, Te and Po (NOTE: staircase).

FORMULA: VBrO₄ (WRONG)

VANADIUM(ROMAN NUMERAL) PERBROMATE You have specified an incorrect charge for the transition metal cation (positive ion) in this compound. Reconsider the charge of the anion (negative ion) and/or the ratio of cations to anions in the compound.

34. Which of the following is a molecular compound?

N₂O Nitrous oxide, N₂O, contains nonmetal atoms of two different elements, and is therefore a molecular compound.