Chemistry Midterm Review Guide

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1 Name: Class: Date: ID: A Chemistry Midterm Review Guide Essay 1. How did Lavoisier transform the field of chemistry in the late 1700s? 2. Explain on what basis the elements in the periodic table are arranged and how that contributes to the usefulness of the periodic table. 3. State the law of conservation of mass. Then apply the law to this question: What would be the total mass of the products of a reaction in which 10 grams of water decomposes into the elements hydrogen and oxygen? 4. Explain the difference between precision and accuracy. Suppose you made three different mass measurements of a sugar sample you knew to have a mass of 1 g. How would you know whether or not the measurements were accurate? How would you know whether or not they were precise? Could the three measurements be precise, but not accurate? Explain. 1

2 Name: ID: A 5. Describe the rules that are used to determine the number of significant figures in the results of addition, subtraction, multiplication, and division. 6. What observations by Rutherford led to the hypothesis that atoms are mostly empty space, and that almost all of the mass of the atom is contained in an atomic nucleus? 7. Explain how the atoms of one element differ from those of another element. 8. Describe the shapes and relative energies of the s, p, d, and f atomic orbitals. 2

3 Name: ID: A 9. Describe the different principles that govern the building of an electron configuration. 10. Describe the trends in the atomic size of elements within groups and across periods in the periodic table. Provide examples. 11. Positive ions are smaller than the atoms from which they are formed, but negative ions are larger than the atoms from which they are formed. Explain why this is so. 12. Explain how atoms (ions) are held together in an ionic bond. Give an example of an ionic compound. 13. Why must each cation in an ionic solid be surrounded by anions? 3

4 Name: ID: A 14. Explain what is meant by orbital hybridization. Give an example of a molecule in which orbital hybridization occurs. 15. What are dispersion forces? How is the strength of dispersion forces related to the number of electrons in a molecule? Give an example of molecules that are attracted to each other by dispersion forces. 16. Given the name of a binary molecular compound, describe how to write its formula. Use carbon tetrachloride as an example. 4

5 Name: ID: A 17. Name the compounds CuBr 2, SCl 2, and BaF 2. Explain the use or omission of the Roman numeral (II) and the prefix di-. 5

6 ID: A Chemistry Midterm Review Guide Answer Section ESSAY 1. ANS: Lavoisier helped transform chemistry from a science of observation to a science of measurement. Toward this end, he developed a balance that could measure small differences in mass. He was part of a general movement toward basing conclusions on experimental evidence. PTS: 1 DIF: L2 REF: p. 15 OBJ: Describe how Lavoisier transformed chemistry. BLM: analysis 2. ANS: The elements in the periodic table are separated into groups according to a set of repeating properties. In each vertical column of the periodic table, called a group, the elements have similar chemical and physical properties. This allows you to easily compare the properties of one element (or a group of elements) to another element (or group of elements). PTS: 1 DIF: L3 REF: p. 46 p. 47 OBJ: Explain how a periodic table is useful. BLM: evaluation 3. ANS: The law of conservation of mass states that in any physical change or chemical reaction, mass is neither created nor destroyed. According to this law, the total mass the products in the decomposition of water would be 10 grams. The total mass of the products would be the same mass as the total mass of the reactants. PTS: 1 DIF: L2 REF: p. 50 OBJ: Describe how the mass of the reactants and the mass of the products of a chemical reaction are related. BLM: application 4. ANS: Precision is the reproducibility of a measurement made under the same conditions; accuracy is the closeness of a measurement to the true value of the measurement. The three measurements would be precise if they were very close to each other in value; they would be accurate if they were close to the actual 1-g mass of the sample. If the measurements are very close to each other, they are precise, regardless of how close they are to the real value. Therefore, the measurements could be precise, but not accurate. PTS: 1 DIF: L3 REF: p. 64 OBJ: Evaluate accuracy and precision. BLM: analysis 5. ANS: The answer of an addition or subtraction can have no more digits to the right of the decimal point than are contained in the measurement with the least number of digits to the right of the decimal point. The answer of a multiplication or division can have no more significant figures than the measurement having the least number of significant figures. For multiplication and division, the position of the decimal point has nothing to do with the number of significant figures. PTS: 1 DIF: L3 REF: p. 70 p. 71 OBJ: Explain why measurements must be reported to the correct number of significant figures. BLM: synthesis 1

7 ID: A 6. ANS: Rutherford s gold-foil experiment led to this hypothesis. Alpha particles were observed to mostly pass through a gold foil, which suggests that the volume of individual gold atoms consists mainly of empty space. The observation that some alpha particles were scattered at large angles led to the suggestion that the gold atom has a central core, or nucleus, composed of a concentrated mass capable of deflecting the alpha particles. PTS: 1 DIF: L2 REF: p. 108 OBJ: Describe the structure of atoms according to the Rutherford model. BLM: comprehension 7. ANS: Different elements have different numbers of protons in their nuclei. All atoms of the same element have the same number of protons. Because atoms are neutral, the number of electrons in an atom equals the number of protons. PTS: 1 DIF: L2 REF: p. 112 OBJ: Explain what makes one element different from another. BLM: analysis 8. ANS: An s orbital has the shape of a sphere and is the orbital having the lowest energy. A p orbital is dumbbell-shaped and has the next higher energy. A d orbital has a more complex shape and a higher energy than either an s orbital or a p orbital. An f orbital has the highest energy of these four orbital types; this orbital has a very complex shape. PTS: 1 DIF: L2 REF: p. 129 p. 131 OBJ: Describe what Bohr proposed in his model of the atom Explain how sublevels of principal energy levels differ. BLM: analysis 9. ANS: The aufbau principle states that electrons enter the orbitals of lowest energy first. The Pauli exclusion principle states that each orbital can hold only two electrons. Hund's rule states that electrons first enter separate orbitals of the same energy, with each electron having the same spin, before pairing with electrons that have opposite spins. PTS: 1 DIF: L2 REF: p. 133 p. 134 OBJ: List the three rules for writing the electron configurations of elements. BLM: analysis 10. ANS: Atomic size increases with increasing atomic number within a group. For example, sodium atoms are larger than lithium atoms, and potassium atoms are larger than sodium atoms. Atomic size decreases with increasing atomic number across a period. For example, lithium atoms are larger than beryllium atoms, and beryllium atoms are larger than boron atoms. PTS: 1 DIF: L2 REF: p. 174 p. 175 OBJ: Describe trends among elements for atomic size. BLM: analysis 2

8 ID: A 11. ANS: When an electron is added to an atom, the attraction of the nucleus for any one electron decreases and the size of the ion s radius increases. When an electron is removed from an atom, there is an increase in the nuclear attraction experienced by the remaining electrons. Consequently, the remaining electrons are drawn closer to the nucleus. PTS: 1 DIF: L2 REF: p. 179 p. 180 OBJ: Describe periodic trends for first ionization energy, ionic size, and electronegativity. BLM: comprehension 12. ANS: In an ionic bond, oppositely charged ions are held together by the electronic force of attraction that exists between oppositely charged particles. In the ionic compound, anions and cations are present in a ratio that causes the total charge on the compound to be zero. Sodium phosphide, Na 3 P, has three sodium ions for each phosphide ion. This ratio insures a zero total charge given the charges on the two individual ions (Na = 1+, P = 3 ). PTS: 1 DIF: L3 REF: p. 201 p. 202 OBJ: Explain the electrical charge of an ionic compound. BLM: application 13. ANS: In this arrangement, like-charged ions are shielded from each other and electronic repulsion is reduced. Also, the force of attraction between oppositely charged ions is maximized. Each of these events contributes to a lowering of energy and an increase in stability of the ionic compound. PTS: 1 DIF: L2 REF: p. 201 p. 202 OBJ: Describe three properties of ionic compounds. BLM: comprehension 14. ANS: In orbital hybridization, two or more different atomic orbitals mix to form the same total number of equivalent hybrid orbitals. For instance, the s and p orbitals of an atom combine to make hybrid orbitals having the character of both the s orbital and the p orbital. These hybrid orbitals are equivalent. Orbital hybridization occurs in the methane molecule in which one 2s orbital and three 2p orbitals hybridize to form four sp 3 orbitals. PTS: 1 DIF: L3 REF: p. 244 OBJ: Identify the ways in which orbital hybridization is useful in describing molecules. BLM: application 15. ANS: Dispersion forces are the weakest of all molecular interactions, and are thought to be caused by the motion of electrons. Generally, the strength of dispersion forces increases as the number of electrons in a molecule increases. Diatomic molecules of halogen elements are an example of molecules whose attraction for one another is caused by dispersion forces. PTS: 1 DIF: L3 REF: p. 251 OBJ: Evaluate the strengths of intermolecular attractions compared with the strengths of ionic and covalent bonds. BLM: synthesis 3

9 ID: A 16. ANS: Begin by writing the chemical symbol for the first element in the compound name on the left, and then write the chemical symbol for the next element on the right. Prefixes that describe elements in the compound names determine the subscripts for those elements. For example, to write the formula for carbon tetrachloride, first write the symbols for the chemical elements as indicated in the name CCl. Next, the tetra in front of chloride indicates the presence of 4 chlorine atoms, which should be indicated by the subscript 4. Therefore, the correct formula is CCl 4. PTS: 1 DIF: L2 REF: p. 282 p. 283 OBJ: Apply the rules for naming and writing formulas for binary molecular compounds List the general guidelines that can help you write the name and formula of a chemical compound. BLM: application 17. ANS: CuBr 2 is copper(ii) bromide. The name must include a Roman numeral because copper is a transition element that can form ions with more than one charge. SCl 2 is sulfur dichloride. The compound is named with prefixes because sulfur and chlorine are both nonmetals and thus form a molecular compound. BaF 2 is barium fluoride. A Roman numeral is not needed in this name because barium is a Group A metal and forms only the 2+ ion. Prefixes are not used in ionic compounds. PTS: 1 DIF: L3 REF: p. 292 p. 293 OBJ: List the general guidelines that can help you write the name and formula of a chemical compound. BLM: analysis 4

Name: Class: Date: ID: A

Name: Class: Date: ID: A Name: Class: _ Date: _ ID: A EOC review II Matching Match each item with the correct statement below. a. atomic orbital d. ground state b. aufbau principle e. Pauli exclusion principle c. electron configuration