CHAPTER 2 Essay Q's
Using the periodic table, predict whether the following compounds are ionic or covalent: (a) SO2 (b) CaF2 (c) N2H4 (d) Al2(SO4)3
(a) molecular; (b) ionic; (c) molecular; (d) ionic
Give the group name for each of the following elements: (a) krypton (b) selenium (c) barium (d) lithium
(a) noble gas; (b) chalcogen; (c) alkaline earth metal; (d) alkali metal
The existence of isotopes violates one of the original ideas of Dalton's atomic theory. Which one?
Dalton originally thought that all atoms of a particular element had identical properties, including mass. Thus, the concept of isotopes, in which an element has different masses, was a violation of the original idea. To account for the existence of isotopes, the second postulate of his atomic theory was modified to state that atoms of the same element must have identical chemical properties.
proton
positively charged, subatomic particle located in the nucleus
neutron
uncharged, subatomic particle located in the nucleus
Write the symbol for each of the following ions: (a) the ion with a 1+ charge, atomic number 55, and mass number 133 (b) the ion with 54 electrons, 53 protons, and 74 neutrons (c) the ion with atomic number 15, mass number 31, and a 3− charge (d) the ion with 24 electrons, 30 neutrons, and a 3+ charge
(a) 133Cs+; (b) 127I−; (c) 31P3−; (d) 57Co3+
Write a symbol for each of the following neutral isotopes. Include the atomic number and mass number for each. (a) the alkali metal with 11 protons and a mass number of 23 (b) the noble gas element with 75 neutrons in its nucleus and 54 electrons in the neutral atom (c) the isotope with 33 protons and 40 neutrons in its nucleus (d) the alkaline earth metal with 88 electrons and 138 neutrons
(a) 23 11 Na; (b) 129 54 Xe; (c) 73 33 As; (d) 226 88Ra
Give the number of protons, electrons, and neutrons in neutral atoms of each of the following isotopes: (a) 7 3 Li (b) 125 52 Te (c) 109 47 Ag (d) 15 7 N (e) 31 15 P
(a) 3 protons, 3 electrons, 4 neutrons; (b) 52 protons, 52 electrons, 73 neutrons; (c) 47 protons, 47 electrons, 62 neutrons; (d) 7 protons, 7 electrons, 8 neutrons; (e) 15 protons, 15 electrons, 16 neutrons
Determine the empirical formulas for the following compounds: (a) caffeine, C8H10N4O2 (b) fructose, C12H22O11 (c) hydrogen peroxide, H2O2 (d) glucose, C6H12O6 (e) ascorbic acid (vitamin C), C6H8O6
(a) C4H5N2O; (b) C12H22O11; (c) HO; (d) CH2O; (e) C3H4O3
For each of the following pairs of ions, write the formula of the compound they will form: (a) Ca2+, S2− (b) NH4+, SO42− (c) Al3+, Br− (d) Na+, HPO42− (e) Mg2+, PO43−
(a) CaS; (b) (NH4)2SO4; (c) AlBr3; (d) Na2HPO4; (e) Mg3 (PO4)2
Open the Build an Atom simulation and click on the Atom icon. (a) Pick any one of the first 10 elements that you would like to build and state its symbol. (b) Drag protons, neutrons, and electrons onto the atom template to make an atom of your element. State the numbers of protons, neutrons, and electrons in your atom, as well as the net charge and mass number. (c) Click on "Net Charge" and "Mass Number," check your answers to (b), and correct, if needed. (d) Predict whether your atom will be stable or unstable. State your reasoning. (e) Check the "Stable/Unstable" box. Was your answer to (d) correct? If not, first predict what you can do to make a stable atom of your element, and then do it and see if it works. Explain your reasoning.
(a) Carbon-12, 12C; (b) This atom contains six protons and six neutrons. There are six electrons in a neutral 12C atom. The net charge of such a neutral atom is zero, and the mass number is 12. (c) The preceding answers are correct. (d) The atom will be stable since C-12 is a stable isotope of carbon. (e) The preceding answer is correct. Other answers for this exercise are possible if a different element of isotope is chosen.
Write the formulas of the following compounds: (a) chlorine dioxide (b) dinitrogen tetraoxide (c) potassium phosphide (d) silver(I) sulfide (e) aluminum nitride (f) silicon dioxide
(a) ClO2; (b) N2O4; (c) K3P; (d) Ag2S; (e) AlN; (f) SiO2
Write the formulas of the following ionic compounds: (a) chromium(III) phosphide (b) mercury(II) sulfide (c) manganese(II) phosphate (d) copper(I) oxide (e) chromium(VI) fluoride
(a) CrP; (b) HgS; (c) Mn3(PO4)2; (d) Cu2O; (e) CrF6
Using the periodic table, identify the lightest member of each of the following groups: (a) noble gases (b) alkaline earth metals (c) alkali metals (d) chalcogens
(a) He; (b) Be; (c) Li; (d) O
The following are properties of isotopes of two elements that are essential in our diet. Determine the number of protons, neutrons and electrons in each and name them. (a) atomic number 26, mass number 58, charge of 2+ (b) atomic number 53, mass number 127, charge of 1−
(a) Iron, 26 protons, 24 electrons, and 32 neutrons; (b) iodine, 53 protons, 54 electrons, and 74 neutrons
The following ionic compounds are found in common household products. Write the formulas for each compound: (a) potassium phosphate (b) copper(II) sulfate (c) calcium chloride (d) titanium(IV) oxide (e) ammonium nitrate (f) sodium bisulfate (the common name for sodium hydrogen sulfate)
(a) K3PO4; (b) CuSO4; (c) CaCl2; (d) TiO2; (e) NH4NO3; (f) NaHSO4
(a) Drag protons, neutrons, and electrons onto the atom template to make a neutral atom of Lithium-6 and give the isotope symbol for this atom. (b) Now remove one electron to make an ion and give the symbol for the ion you have created.
(a) Lithium-6 contains three protons, three neutrons, and three electrons. The isotope symbol is 6Li or 63Li. (b) 6Li+ or 63Li+
Write the formulas for the following compounds: (a) phosphorus pentachloride (b) dinitrogen monoxide (c) iodine heptafluoride (d) carbon tetrachloride
(a) PCl5; (b) N2O; (c) IF7; (d) CCl4
Write the formulas of the following compounds: (a) rubidium bromide (b) magnesium selenide (c) sodium oxide (d) calcium chloride (e) hydrogen fluoride (f) gallium phosphide (g) aluminum bromide (h) ammonium sulfate
(a) RbBr; (b) MgSe; (c) Na2O; (d) CaCl2; (e) HF; (f) GaP; (g) AlBr3; (h) (NH4)2SO4
Predict and test the behavior of α particles fired at a Rutherford atom model. (a) Predict the paths taken by α particles that are fired at atoms with a Rutherford atom model structure. Explain why you expect the α particles to take these paths. (b) If α particles of higher energy than those in (a) are fired at Rutherford atoms, predict how their paths will differ from the lower-energy α particle paths. Explain your reasoning. (c) Predict how the paths taken by the α particles will differ if they are fired at Rutherford atoms of elements other than gold. What factor do you expect to cause this difference in paths, and why? (d) Now test your predictions from (a), (b), and (c). Open the Rutherford Scattering simulation and select the "Rutherford Atom" tab. Due to the scale of the simulation, it is best to start with a small nucleus, so select "20" for both protons and neutrons, "min" for energy, show traces, and then start firing α particles. Does this match your prediction from (a)? If not, explain why the actual path would be that shown in the simulation. Pause or reset, set energy to "max," and start firing α particles. Does this match your prediction from (b)? If not, explain the effect of increased energy on the actual path as shown in the simulation. Pause or reset, select "40" for both protons and neutrons, "min" for energy, show traces, and fire away. Does this match your prediction from (c)? If not, explain why the actual path would be that shown in the simulation. Repeat this with larger numbers of protons and neutrons. What generalization can you make regarding the type of atom and effect on the path of α particles? Be clear and specific.
(a) The Rutherford atom has a small, positively charged nucleus, so most α particles will pass through empty space far from the nucleus and be undeflected. Those α particles that pass near the nucleus will be deflected from their paths due to positive-positive repulsion. The more directly toward the nucleus the α particles are headed, the larger the deflection angle will be. (b) Higher-energy α particles that pass near the nucleus will still undergo deflection, but the faster they travel, the less the expected angle of deflection. (c) If the nucleus is smaller, the positive charge is smaller and the expected deflections are smaller—both in terms of how closely the α particles pass by the nucleus undeflected and the angle of deflection. If the nucleus is larger, the positive charge is larger and the expected deflections are larger—more α particles will be deflected, and the deflection angles will be larger. (d) The paths followed by the α particles match the predictions from (a), (b), and (c).
Name the following compounds: (a) CsCl (b) BaO (c) K2S (d) BeCl2 (e) HBr (f) AlF3
(a) cesium chloride; (b) barium oxide; (c) potassium sulfide; (d) beryllium chloride; (e) hydrogen bromide; (f) aluminum fluoride
Each of the following compounds contains a metal that can exhibit more than one ionic charge. Name these compounds: (a) Cr2O3 (b) FeCl2 (c) CrO3 (d) TiCl4 (e) CoO (f) MoS2
(a) chromium(III) oxide; (b) iron(II) chloride; (c) chromium(VI) oxide; (d) titanium(IV) chloride; (e) cobalt(II) oxide; (f) molybdenum(IV) sulfide
For each of the following compounds, state whether it is ionic or covalent. If it is ionic, write the symbols for the ions involved: (a) NF3 (b) BaO (c) (NH4)2CO3 (d) Sr(H2PO4)2 (e) IBr (f) Na2O
(a) covalent; (b) ionic, Ba2+, O2−; (c) ionic, NH4+, CO32−; (d) ionic, Sr2+, H2PO4−; (e) covalent; (f) ionic, Na+, O2−
Use the Build a Molecule simulation to repeat Exercise, but build a molecule with two carbons, six hydrogens, and one oxygen. (a) Draw the structural formula of this molecule and state its name. (b) Can you arrange these atoms to make a different molecule? If so, draw its structural formula and state its name. (c) How are the molecules drawn in (a) and (b) the same? How do they differ? What are they called (the type of relationship between these molecules, not their names).
(a) ethanol A Lewis Structure is shown. An oxygen atom is bonded to a hydrogen atom and a carbon atom. The carbon atom is bonded to two hydrogen atoms and another carbon atom. That carbon atom is bonded to three more hydrogen atoms. There are a total of two carbon atoms, six hydrogen atoms, and one oxygen atoms. (b) methoxymethane, more commonly known as dimethyl ether A Lewis Structure is shown. An oxygen atom is bonded to two carbon atoms. Each carbon atom is bonded to three different hydrogen atoms. There are a total of two carbon atoms, six hydrogen atoms, and one oxygen atom. (c) These molecules have the same chemical composition (types and number of atoms) but different chemical structures. They are structural isomers.
Use the periodic table to give the name and symbol for each of the following elements: (a) the noble gas in the same period as germanium (b) the alkaline earth metal in the same period as selenium (c) the halogen in the same period as lithium (d) the chalcogen in the same period as cadmium
(a) krypton, Kr; (b) calcium, Ca; (c) fluorine, F; (d) tellurium, Te
What are the IUPAC names of the following compounds? (a) manganese dioxide (b) mercurous chloride (Hg2Cl2) (c) ferric nitrate [Fe(NO3)3] (d) titanium tetrachloride (e) cupric bromide (CuBr2)
(a) manganese(IV) oxide; (b) mercury(I) chloride; (c) iron(III) nitrate; (d) titanium(IV) chloride; (e) copper(II) bromide
Using the periodic table, classify each of the following elements as a metal or a nonmetal, and then further classify each as a main-group (representative) element, transition metal, or inner transition metal: (a) uranium (b) bromine (c) strontium (d) neon (e) gold (f) americium (g) rhodium (h) sulfur (i) carbon (j) potassium
(a) metal, inner transition metal; (b) nonmetal, representative element; (c) metal, representative element; (d) nonmetal, representative element; (e) metal, transition metal; (f) metal, inner transition metal; (g) metal, transition metal; (h) nonmetal, representative element; (i) nonmetal, representative element; (j) metal, representative element
law of definite proportions
(also, law of constant composition) all samples of a pure compound contain the same elements in the same proportions by mass
law of constant composition
(also, law of definite proportions) all samples of a pure compound contain the same elements in the same proportions by mass
A sample of magnesium is found to contain 78.70% of 24Mg atoms (mass 23.98 amu), 10.13% of 25Mg atoms (mass 24.99 amu), and 11.17% of 26Mg atoms (mass 25.98 amu). Calculate the average mass of a Mg atom.
24.31 amu
Naturally occurring copper consists of 63Cu (mass 62.9296 amu) and 65Cu (mass 64.9278 amu), with an average mass of 63.546 amu. What is the percent composition of Cu in terms of these two isotopes?
69.15% Cu-63 and 30.85% Cu-65
An ion of platinum has a mass number of 195 and contains 74 electrons. How many protons and neutrons does it contain, and what is its charge?
78 protons; 117 neutrons; charge is 4+
Average atomic masses listed by IUPAC are based on a study of experimental results. Bromine has two isotopes 79Br and 81Br, whose masses (78.9183 and 80.9163 amu) and abundances (50.69% and 49.31%) were determined in earlier experiments. Calculate the average atomic mass of bromine based on these experiments.
79.904 amu
Aluminum and carbon react to form an ionic compound. Predict which forms an anion, which forms a cation, and the charges of each ion. Write the symbol for each ion and name them.
Al will form a cation with a charge of 3+: Al3+, an aluminum ion. Carbon will form an anion with a charge of 4−: C4−, a carbide ion.
How are protons and neutrons similar? How are they different?
Both are subatomic particles that reside in an atom's nucleus. Both have approximately the same mass. Protons are positively charged, whereas neutrons are uncharged.
Using the periodic table, predict whether the following chlorides are ionic or covalent: KCl, NCl3, ICl, MgCl2, PCl5, and CCl4.
Ionic: KCl, MgCl2; Covalent: NCl3, ICl, PCl5, CCl4
Predict the formula of the ionic compound formed between the lithium ion and the peroxide ion, O22− (Hint: Use the periodic table to predict the sign and the charge on the lithium ion.)
Li2O2
A molecule of metaldehyde (a pesticide used for snails and slugs) contains 8 carbon atoms, 16 hydrogen atoms, and 4 oxygen atoms. What are the molecular and empirical formulas of metaldehyde?
Molecular formula, C8H16O4; empirical formula, C2H4O
Predict the formula of the ionic compound formed between the sodium cation, Na+, and the sulfide anion, S2−.
Na2S
Give the symbol and name for the ion with 34 protons and 36 electrons.
Se2−, the selenide ion
Explain why the symbol for an atom of the element oxygen and the formula for a molecule of oxygen differ.
The symbol for the element oxygen, O, represents both the element and one atom of oxygen. A molecule of oxygen, O2, contains two oxygen atoms; the subscript 2 in the formula must be used to distinguish the diatomic molecule from two single oxygen atoms.
Identify the postulate of Dalton's theory that is violated by the following observations: 59.95% of one sample of titanium dioxide is titanium; 60.10% of a different sample of titanium dioxide is titanium.
This statement violates Dalton's fourth postulate: In a given compound, the numbers of atoms of each type (and thus also the percentage) always have the same ratio.
The average atomic masses of some elements may vary, depending upon the sources of their ores. Naturally occurring boron consists of two isotopes with accurately known masses (10B, 10.0129 amu and 11B, 11.0931 amu). The actual atomic mass of boron can vary from 10.807 to 10.819, depending on whether the mineral source is from Turkey or the United States. Calculate the percent abundances leading to the two values of the average atomic masses of boron from these two countries.
Turkey source: 26.49% (of 10.0129 amu isotope); US source: 25.37% (of 10.0129 amu isotope)
isotopes
atoms that contain the same number of protons but different numbers of neutrons
nucleus
massive, positively charged center of an atom made up of protons and neutrons
electron
negatively charged, subatomic particle of relatively low mass located outside the nucleus
alpha particle (α particle)
positively charged particle consisting of two protons and two neutrons
Dalton's atomic theory
set of postulates that established the fundamental properties of atoms
law of multiple proportions
when two elements react to form more than one compound, a fixed mass of one element will react with masses of the other element in a ratio of small whole numbers
