Ch.2 - Atoms & ElementsSee all chapters
All Chapters
Ch.1 - Intro to General Chemistry
Ch.2 - Atoms & Elements
Ch.3 - Chemical Reactions
BONUS: Lab Techniques and Procedures
BONUS: Mathematical Operations and Functions
Ch.4 - Chemical Quantities & Aqueous Reactions
Ch.5 - Gases
Ch.6 - Thermochemistry
Ch.7 - Quantum Mechanics
Ch.8 - Periodic Properties of the Elements
Ch.9 - Bonding & Molecular Structure
Ch.10 - Molecular Shapes & Valence Bond Theory
Ch.11 - Liquids, Solids & Intermolecular Forces
Ch.12 - Solutions
Ch.13 - Chemical Kinetics
Ch.14 - Chemical Equilibrium
Ch.15 - Acid and Base Equilibrium
Ch.16 - Aqueous Equilibrium
Ch. 17 - Chemical Thermodynamics
Ch.18 - Electrochemistry
Ch.19 - Nuclear Chemistry
Ch.20 - Organic Chemistry
Ch.22 - Chemistry of the Nonmetals
Ch.23 - Transition Metals and Coordination Compounds

Modern Atomic Theory states that matter is composed of small, indivisible particles called atoms. 

Three Laws of Modern Atomic Theory

Concept #1: The Conservation of Matter

The Law of Conservation of Mass states that matter can neither be created nor destroyed, all that happens is that it changes forms. 

Concept #2: Law of Definite Proportions

No matter where you obtain a compound, whether it’s from a lab experiment or from collection out in the field, the ratio of elements in it will remain constant. 

Concept #3: Law of Multiple Proportions

When element A and element B combine they can form different compounds in different ratios to one another. Dividing these different ratios should generate whole number answers. 

Example #1: A 15.39 g sample of iodine reacts with 62.92 g of chlorine to form iodine pentachloride, ICl5. If iodine pentachloride is the only product formed calculate its mass. 

Example #2: Two samples sodium fluoride decompose into their constituent elements. The first sample produces 15.8 kg of sodium and 20.1 kg of fluorine. If the second sample produces 192.0 g of sodium, how many grams of fluorine were also produced? 

Practice: Which of the following is an example of the law of multiple proportions?

Additional Problems
In a chemical reaction, matter is neither created or destroyed. Which law does this refer to? A) Law of Definite Proportions B) Law of the Conservation of Mass C) Law of Modern Atomic Theory D) Law of Multiple Proportions E) First Law of Thermodynamics
Drinking alcohol is also called ethyl alcohol or ethanol. Most of the ethanol produced in the USA comes from corn, an obviously natural source. It can also be made in the laboratory from natural gas (CH4) as a starting material. If you wanted to use ethanol from one of these sources, and price were not a consideration, decide which one you would choose. Which of the following laws listed below is most useful to you in making your decision?   a. The Law of Conservation of Mass b. The Law of Definite Proportions c. Dalton’s Atomic Theory d. The Law of Multiple Proportions e. Avogadro’s Hypothesis
Which procedure can be used to demostrate experimentally that this reaction obeys the Law of Conservation of Matter? 2 Mg (s) + O2 (g) → 2 MgO (s) (A) Take a mass of 1.0000 g of Mg ribbon, burn it in pure O2 , and compare the mass of the product with the original mass of the Mg. (B) Show that the sum of two atomic molar masses of Mg plus one molecular mass of O2 is equal to two formula molar masses of MgO. (C) Determine the mass of a sealed flash-bulb containing magnesium and oxygen, ignite the mixture, cool, and compare the final mass of bulb plus contents with the original mass of the bulb plus contents. (D) Burn 1.0000 g of Mg ribbon in a tall beaker filled with air, scrape out all the MgO formed and compare with the original mass of the Mg.
Which of the following sets illustrates the Law of Multiple Proportions?  
The statement, “In a chemical reaction, no matter is neither created nor destroyed.” Is called a. The Law of Conservation of Mass b. Dalton’s Atomic Theory c. The Scientific Methods d. The Law of Multiple Proportions e. The Law of Definite Proportions
Which of the following is NOT a component of Dalton’s Atomic Theory? A. A chemical reaction rearranges the grouping of atoms. B. Atoms are comprised of protons, neutrons, and electrons. C. Atoms of a given element are chemically and physically identical. D. Atoms of different elements combine in simple, whole number ratios to form compounds. E. Matter is composed of atoms, which cannot be created or destroyed.
A compound contains only calcium and fluorine. A sample of the compound is determined to contain 2.00 g of calcium and 1.90 g of fluorine. According to the Law of Definite Proportions, how much calcium should another sample of this compound contain if it contains 2.85 g of fluorine? a. 2.71 g b. 4.00 g c. 3.00 g d. 4.50 g e. 6.00 g
When a log burns, the mass of its products equals the mass of the log and oxygen. This is an example of which law? A. Law of Definite Proportions B. Law of Conservation of Mass C. Law of Multiple Proportions D. Law of Modern Atomic Theory E. First Law of Thermodynamics 
The two compounds, Fe3O4 and Fe2O3, illustrate the law of multiple proportions. For the same mass of iron in samples of each compound, what is the ratio of the masses of the oxygen in the compounds? A. 1 to 1 B. 2 to 3 C. 3 to 4 D. 7 to 8 E. 8 to 9
Which is the correct match of person and the law: when two elements form a series of compounds, the masses of the one element that combine with a fixed mass of the other element stand to one another in the ratio of small whole numbers. A. Democratus, atomic law B. Lavosier, law of conservation of mass C. Berthollet, law of definite proportions D. Dalton, law of multiple proportions E. Avagadro, law of moles
Which of the following statements is FALSE according to Dalton's Atomic Theory? A) An atom of nitrogen can be broken down into smaller particles that will still have the unique properties of nitrogen. B) Atoms combine in simple whole number ratios to form compounds. C) One carbon atom will combine with one oxygen atom to form a molecule of carbon monoxide. D) All atoms of chlorine have identical properties that distinguish them from other elements. E) Atoms of sodium do not change into another element during chemical reaction with chlorine.
Which statements are inconsistent with Dalton's atomic theory as it was originally stated? Why?A. All carbon atoms are identical.B. An oxygen atom combines with 1.5 hydrogen atoms to form a water molecule.C. Two oxygen atoms combine with a carbon atom to form a carbon dioxide molecule.D. The formation of a compound often involves the destruction of one or more atoms.
Which quantity or quantities must always be the same on both sides of a chemical equation?I. the number of atoms of each kindII. the number of molecules of each kindIII. The mass of the reactants is equal to the mass of the products.A. I onlyB. II onlyC. III onlyD. Both I and IIIE. All of the above
A 12.39 g sample of phosphorus reacts with 42.54 g of chlorine to form only phosphorus trichloride (PCl3). If it is the only product, what mass of PCl 3 is formed?A) 140.01 gB) 30.15 gC) 91.86 gD) 79.71 gE) 54.93 g
Which quantity or quantities must always be the same on both sides of a chemical equation? Check all that apply.a. the number of molecules of each kindb. the sum of the masses of all substances involvedc. the number of moles of each kind of moleculed. the number of atoms of each kind
Two samples of potassium iodide are decomposed into their constituent elements. The first sample produced 13.0 g of potassium and 42.3 g of iodine. If the second sample produced 24.4 kg of potassium, how many kg of iodine were produced?A) 13.3 kgB) 22.5 kgC) 79.4 kgD) 44.4 kgE) 92.4 kg
Determine the number of each type of atom in each formula: a. Ca(NO2)2
Determine the number of each type of atom in each formula: b. CuSO4
You have two beakers, one filled to the 100-mL mark with sugar (the sugar has a mass of 180.0 g) and the other filled to the 100-mL mark with water (the water has a mass of 100.0 g). You pour all the sugar and all the water together in a bigger beaker and stir until the sugar is completely dissolved. a. Which of the following is true about the mass of the solution? Explain.i. It is much greater than 280.0 g.ii. It is somewhat greater than 280.0 g.iii. It is exactly 280.0 g.iv. It is somewhat less than 280.0 g.v. It is much less than 280.0 g.
Determine the number of each type of atom in each formula: c. Al(NO3)3
A 7.83-g sample of HCN is found to contain 0.290 g of H and 4.06 g of N. Find the mass of carbon in a sample of HCN with a mass of 3.37 g.
Determine the number of each type of atom in each formula: d. Mg(HCO3)2
The ratio of sulfur to oxygen by mass in SO 2 is 1.0:1.0.a. Find the ratio of sulfur to oxygen by mass in SO 3.b. Find the ratio of sulfur to oxygen by mass in S 2O.
What theory did John Dalton formulate? 
The ratio of oxygen to carbon by mass in carbon monoxide is 1.33:1.00. Find the formula of an oxide of carbon in which the ratio by mass of oxygen to carbon is 2.00:1.00.
Which of the following is an example of the law of multiple proportions?A) A sample of chlorine is found to contain three times as much Cl-35 as Cl-37.B) Two different compounds formed from carbon and oxygen have the following mass ratios: 1.33 g O: 1 g C and 2.66 g O: 1 g C.C) Two different samples of table salt are found to have the same ratio of sodium to chlorine.D) The atomic mass of bromine is found to be 79.90 amu.E) Nitrogen dioxide always has a mass ratio of 2.28 g O: 1 g N.
What observations did Lavoisier make? What law did he formulate? 
Write a ratio showing the relationship between the amounts of each element for each compound: 
Write a ratio showing the relationship between the amounts of each element for each compound:
The ratio of the mass of a nitrogen atom to the mass of an atom of   12C is 7:6 and the ratio of the mass of nitrogen to oxygen in N2O is 7:4. Find the mass of 1 mol of oxygen atoms.
Write a ratio showing the relationship between the amounts of each element for each compound:
 A hydrogen-filled balloon was ignited and 1.50 g of hydrogen reacted with 12.0 g of oxygen. How many grams of water vapor were formed? (Assume that water vapor is the only product.) 
An automobile gasoline tank holds 21 kg of gasoline. When the gasoline burns, 84 kg of oxygen is consumed, and carbon dioxide and water are produced. What is the total combined mass of carbon dioxide and water that is produced? 
The smallest unit of an element that has all of the properties of the element is a/an a. molecule. b. cell. c. atom. d. neutron.
Two samples of carbon tetrachloride were decomposed into their constituent elements. One sample produced 38.9 g of carbon and 448 g of chlorine, and the other sample produced 14.8 g of carbon and 134 g of chlorine. Are these results consistent with the law of definite proportions? Show why or why not. 
A sample of ascorbic acid (vitamin C) is synthesized in the laboratory. It contains 1.50 g of carbon and 2.00 g of oxygen. Another sample of ascorbic acid isolated from citrus fruits contains 6.35 g of carbon. How many grams of oxygen does it contain? Which law are you assuming in answering this question?
The mass ratio of sodium to fluorine in sodium fluoride is 1.21: 1. A sample of sodium fluoride produced 28.8 g of sodium upon decomposition. How much fluorine (in grams) was formed?
Upon decomposition, one sample of magnesium fluoride produced 1.65 kg of magnesium and 2.57 kg of fluorine. A second sample produced 1.32 kg of magnesium. How much fluorine (in grams) did the second sample produce?
Palladium forms three different compounds with sulfur. The mass of sulfur per gram of palladium in each compound is listed below: Show that these masses are consistent with the law of multiple proportions. 
What is the ratio of oxygen atoms to hydrogen atoms in the mineral aluminite Al2(SO4)(OH)4 . 7H2O?a. 8:4b. 15:18c. 18:15d. 15:11e. 11:15
The ratio of oxygen to nitrogen by mass in NO 2 is 2.29. The ratio of fluorine to nitrogen by mass in NF3 is 4.07. Find the ratio of oxygen to fluorine by mass in OF 2.  
Which of the following is an example of the law of multiple proportions? Explaina. Two different samples of water are found to have the same ratio of hydrogen to oxygenb. When hydrogen and oxygen react to form water, the mass of water formed is exactly equal to the mass of hydrogen and oxygen that reacted. c. The mass ratio of oxygen to hydrogen in water is 8:1. The mass ratio of oxygen to hydrogen in hydrogen peroxide. (a compound that only contains hydrogen and oxygen) is 16: 1. 
A sample of H2SO4 contains 2.02 g of hydrogen, 32.07 g of sulfur, and 64.00 g of oxygen. How many grams of sulfur and grams of oxygen are present in a second sample of H2SO4 containing 7.27 g of hydrogen?
Two elements, R and Q, combine to form two binary compounds. In the first compound, 14.0 g of R combines with 3.00 g of Q. In the second compound, 7.00 g of R combines with 4.50 g of Q. Show that these data are in accord with the law of multiple proportions. If the formula of the second compound is RQ, what is the formula of the first compound?
Which of the following chemical reactions is/are NOT possible according to Dalton's atomic theory?a. reaction 1: CCl4 → CH4b. reaction 2: N2 + 3H2 → 2NH3c. reaction 3: 2H2 + O2 → 2H2O + Au
In a reaction, 34.0 g of chromium(III) oxide reacts with 12.1 g of aluminum to produce chromium and aluminum oxide. If 23.3 gof chromium is produced, what mass of aluminum oxide is produced?
How many moles of N are in 0.237 g of N20?
A hydrocarbon is a compound that contains mostly carbon and hydrocarbon, Calculate the percent composition (by mass) of the following hydrocarbon: C6H14. Enter the percentages of carbon and hydrogen numerically to four significant figures, separated by commas. 
How many moles of N are in 0.237 g of N2O?
How many O atoms are there in 7.527 x 1023 molecules of trifluoroacetic acid, C2HF3O2?
Exactly 1 mol of AlPO4 contains how many moles of Al, P. and O? Al = P = O =
The fuel used in many disposable lighters is liquid butane, C4H10. How many carbon atoms are in 2.00 g of butane given that the molar mass of butane is 58.12 g/mol? Express your answer numerically in atoms.
A sample of C3H8 has 4.00 x 1024 H atoms. How many carbon atoms does the sample contain? What is the total mass of the sample?
Use the law of constant composition to complete the following table summarizing the amounts of nitrogen and oxygen produced upon the sample of dinitrogen monoxide. Enter your answers numerically separated by a comma. 
This is the chemical formula for methyl tert-butyl ether (the clean-fuel gasoline additive MTBE): CH3OC(CH3)3 A chemical engineer has determined by measurements that there are 0.0184 moles of carbon in a sample of methyl tert-butyl ether. How many moles of oxygen are in the sample? Round your answer to 3 significant digits.
Answer the following questions using the law of conservation of mass.Consider a hypothetical reaction in which A and B are reactants and C and D are products. If 23 grams of A completely reacts with 29 grams of B to produce 18 grams of C, how many grams of D will be produced? A 3.4 gram sample of sodium hydrogen carbonate is added to a solution of acetic acid weighing 10.1 grams. The two substances react, releasing carbon dioxide gas to the atmosphere. After the reaction, the contents of the reaction vessel weighs 12.1 grams. What is the mass of carbon dioxide released during the reaction?
Element X forms three different compounds with element Y. Based on the information in this table.What are the formulas of compounds 2 and 3? 
Convert the following quantities.6.80 x 1027 P4O10 molecules = 4.077 × 1020 formula units PbCl4 =
Two samples of sodium chloride were decomposed into their constituent elements. One sample produced 2.94 g of sodium and 4.53 g of chlorine. Which of the following could be the results of the decomposition of the other sample, being consistent with the law of constant composition (also called the law of definite proportions or law of definite composition)? a. 5.90 g of sodium and 3.54 g of chlorine b. 5.90 g of sodium and 1.47 g of chlorinec. 5.90 g of sodium and 14.8 g of chlorine d. 5.90 g of sodium and 9.09 g of chlorine