Chemistry Midterm Review

Chemistry Midterm Review DeMario 2007

Question One • Describe the atomic model for each scientist listed. Be sure to mention information about the experiment and the location of the subatomic particles. • Dalton • Thomson • Rutherford • Bohr • Modern View Answer

Answer 1 • Dalton – indivisible, solid sphere (no subatomic particles) • Thomson- “plum pudding model” electrons are evenly distributed throughout a mass of protons. Model based on his cathode ray experiment • Rutherford- discovered mostly empty space surrounding a dense positively charged nucleus using through the gold foil experiment • Bohr- believed in a small positively charged nucleus containing the protons and neutrons surrounded by electrons in ORBITS of specific energy levels • Modern View- Also called the wave- mechanical model and the quantum model similar to Bohr but electrons are in regions of high probability based on energy level, and orbital.

Question 2 • Compare the charge, size, and location of a proton, neutron, and electron. Answer 2

Answer 2

Question 3 • Explain why the following two elements are isotopes. State the number of protons, electrons, and neutrons each isotope possesses.

Answer 3 • They are isotopes because each have a different # of neutrons but the same number of protons and electrons. • Sn -121 has 50 p+, 50 e-, 71 n0 • Sn- 119 has 50 p+, 50 e-, 69 n0

Question 4 • List the seven metalloids

Answer 4 B Si, Ge, As Sb, Te At

Question 5 • Why is the formation of a solution a physical change while the ability to react with a chemical considered a chemical change?

Answer 5 • “reacting” indicates a change in the physical properties of an element resulting in a new compound. • Formation of a solution is a physical property because a new compound has not been formed. Evaporation of the water would leave the original compound behind. (ex. salt dissolving in water)

Question 6 • List Properties of a metal and a nonmetal.

Metals Form cations Shiny Malleable Ductile Good conductors Low electronegativites and IE Solids except Hg Nonmetals Brittle Dull Poor conductors High electronegativities and IE Answer 6

Question 7 • Define allotrope.

Answer 7 • One or more molecular forms of an element in the same physical state; • Example: O2 and O3 Carbon: graphite, diamond, buckyballs • Allotropes are composed of the same element but different composition of atoms results in different properties and different structures.

Question 8 • What is the correct formula for Cobalt(III) bromide?

Answer 8 CoBr3

Question 9 • What form of matter cannot be decomposed?

Answer 9 Element

Question 10 • What happens to a nonmetal ion when it becomes a negative ion? • Mention difference in # of electrons • Changes in radius

Answer 10 • Gains electrons • Radius increases

Question 11 • What is the name of the property that indicates an element’s desire to attract electrons and which element has the greatest attraction?

Answer 11 • Electronegativity • Fluorine

Question 12 • What are the terms used to identify a pure substance? • What are the terms used to identify a mixture?

Answer 12 • Element and compound • Heterogeneous and Homogeneous

Question 13 • What is the difference between an excited state electron and a ground state electron?

Answer 13 • Ground state electrons are in the lowest energy state • Excited state electrons have absorbed energy allowing them to jump to a higher energy level.

Question 14 What are the three assumptions made regarding particle behavior in the KMT [Kinetic Molecular Theory]?

Answer 14 • Gas particles are small, hard spheres with insignificant volumes • Particle’s motion is rapid, constant, and random straight-line motion • Particle collisions are perfectly elastic

Question 15 • What is the name for each type of phase change? • Solid liquid • Liquid  gas • Gas  liquid • Liquid  solid • Solid  gas

Answer 15 • Melting • Boiling or vaporization • Condensation • Freezing / solidification • Sublimation

Question 16 • According to Avogadro's Hypothesis two samples of gas that have the same volume and are at the same temperature and pressure will _______________.

Answer 16 • Have the same numbers of particles

Question 17 • Thermal energy from a cold pack travels in which direction when applied to the leg?

Answer 17 Hot  cold Leg  cold pack

Question 18 Under what conditions will a real gas behave ideally?

Answer 18 • High temperature [so that the particles are moving fast] • Low pressure [ so that particles are far apart to avoid attraction]

Question 19 • What is the % composition by mass of carbon in carbon dioxide [gram-formula mass 44 grams/mole]?

Answer 19 27 % C

Question 20 • Why does calcium have similar chemical properties to barium?

Answer 20 • Both are Group 2 elements • Both have the same number of valence electrons

Question 21 • Which of the following terms indicate a chemical property and which indicate a physical property? • Flatten • Conduct • Corrode • Drawn into a wire • React

Chemical Corrode react Physical Flatten Drawn Conduct Answer 21

Question 22 • What is the charge on a I-127 nucleus?

Answer 22 +53

Question 23 Name the type of element as it appears in the order below. Ge  K  Ar  Br

Answer 23 Ge  K  Ar  Br Metalloid, metal, noble gas, nonmetal

Question 24 How many electrons are contained in an Cu2+ ion?

Answer 24 27 electrons

Question 25 Which electron configuration represents the electrons of atom of sodium in the excited? • 2-8-1 • 2-8-2 • 2-7-3 • 2-7-2

Chemistry Midterm Review