DEC 10 CHEM TEST

A helium nucleus has two protons and two neutrons. How many electrons would it take to equal the mass of a helium nucleus?

One electron has a mass that is about 2 000 times smaller than a proton. The mass of a proton is about the same as the mass of an electron. We would need 2 000 electrons to equal the mass of 1 protons, meaning we would need 8 000 electrons to equal the mass of a helium nucleus, or alpha particle.

The radioactive decay of 146 C to 147N occurs by the process of a. beta particle emission. b. alpha particle emission. c. positron emission. d. electron capture. e. neutron capture.

a When C-16 goes through a decay, N-16 is one of the products. The mass numbers of the two nuclides stay the same, but the atomic number increases - this means a neutron has changed into a proton. When a neutron changes into a proton, this is beta decay - where an electron is formed in the nucleus and released. 166C 167N + 0-1e

Which of the following elements is utilized as a shield from sources of radiation? a. Pb b. Ca c. Zn d. As e. Na

a if we reread question number 6, it asks which radiation would penetrate a piece of LEAD the best. This means the answer we are looking for is LEAD. Na is sodium, As is arsenic, Zn is zinc, Ca is calcium, therefore Pb must be the answer.

List the symbol and atomic number of each element. a. Boron b. Mercury c. Curium

a. Boron 5B b. Mercury 80Hg c. Curium 96Cm

To what group number does each element belong? a. Germanium b. Nitrogen c. Boron

a. Germanium- 14 b. Nitrogen- 15 c. Boron- 13

Which statements about electrons are false? Please correct the false statements. a. Most atoms have more electrons than protons. b. Electrons have a charge of -1. c. If an atom has an equal number of protons and electrons, it will be charged neutral. d. Electrons experience an attraction to protons.

a. Most atoms have more electrons than protons. False. Atoms are neutral. This means the number of electrons and protons are the same. b. Electrons have a charge of -1. True. Protons are +1, neutrons are neutral with a charge of 0. c. If an atom has an equal number of protons and electrons, it will be charged neutral. True. Atoms are neutral. This means the number of electrons and protons are the same. d. Electrons experience an attraction to protons. True. Electrons are negative and protons are positive. Opposites attract.

Classify each element as a metal, nonmetal, or metalloid. a. Na b. Si c. Br d. Ag

a. Na - group 1, alkali METALS b. Si- There are 7 metalloids, Si is one of them. c. Br- group 17, halogens, it is a nonmetal d. Ag- group 11, transition element / metal

Classify each element as a halogen, a noble gas, or neither. a. Ne b. Br c. S d. Xe e. I

a. Ne - noble gas b. Br- halogen c. S- neither d. Xe- noble gas e. I- halogen

Which element do you expect to be most like magnesium? Why? a. Potassium b. Bromine c. Calcium

a. Potassium- no b. Bromine- no c. Calcium- yes - because it is in the same group (family) as Magnesium.

Which statements about protons are false? Please correct the false statements. a. Protons have about the same mass as neutrons. b. Protons have about the same mass as electrons. c. Some atoms don't have any protons. d. Protons have the same magnitude of charge as neutrons but are opposite in sign.

a. Protons have about the same mass as neutrons. True. Protons and neutrons have about the same mass. b. Protons have about the same mass as electrons. False. The mass of an electron is negligible compared to the masses of protons and neutrons. It is about 2000 smaller than a proton. c. Some atoms don't have any protons. False. If it is an atom, it is an element. If it is an element, it has an atomic number. If it has an atomic number, it has protons. d. Protons have the same magnitude of charge as neutrons but are opposite in sign. False. Protons are positive in charge, neutrons are neutral. This means they have a charge of zero.

Which elements are alkaline earth metals? a. Rubidium b. Tungsten c. Magnesium d. Cesium e. Beryllium

a. Rubidium- group 1, alkali METAL b. Tungsten- transition metal c. Magnesium- group 1, alkali METALS d. Cesium- group 1, alkali METAL e. Beryllium- group 2, alkaline earth METAL

Which elements are alkali metals? a. Scandium b. Iron c. Potassium d. Lithium e. Cobalt

a. Scandium- transition metal b. Iron- transition metal c. Potassium- group 1, alkali METALS d. Lithium- group 1, alkali METALS e. Cobalt- transition metal

Find the atomic number (Z) for each element. a. Si b. W c. Ni

a. Si 14 b. W 74 c. Ni 27

Which element is a period 5 transition element? a. Sr b. Pd c. P d. V

a. Sr- in period 5, but an alkaline earth metal b. Pd - in period 5 AND a transition element (metal) in group 10. c. P-ingroup15,inperiod3 d. V - in group 5, a transition element (metal) but in period 4

How many protons are in the nucleus of an atom of each element? a. Ti b. Li c. U

a. Ti 22 b. Li 3 c. U 90

Which pair of elements do you expect to be most similar? a. Ti and Ga b. N and O c. Li and Na d. Ar and Br e. Ge and Ga

a. Ti and Ga- they are in the same period b. N and O - they are in the same period c. Li and Na - they are in the same group - they should be most similar d. Ar and Br - they are in two different groups AND two different periods. e. Ge and Ga - they are in the same period

Write the symbol for each isotope in the form AZX. a. U-235 23592U b. V-52 c. P-32

a. U-235 23592U b. V-52 5223V c. P-32 3215P

List the name and the atomic number of each element. a. Y b. K c. Mo

a. Y - yttrium, 39 b. K- potassium, 19 c. Mo- molybdenum, 42

How many neutrons are in an atom with each atomic number and mass number? a. Z=28,A=59 b. Z=92,A=235 c. Z=21,A=46 d. Z=18,Z=42

a. Z=28,A=59-31neutrons b. Z=92,A=235-143neutrons c. Z=21,A=46-25neutrons d. Z=18,Z=42-24neutrons

Write isotopic symbols for each isotope. a. the iodine isotope with 74 neutrons b. the phosphorus isotope with 16 neutrons c. the uranium isotope with 234 neutrons d. the argon isotope with 22 neutrons

a. the iodine isotope with 74 neutrons - 12753I b. the phosphorus isotope with 16 neutrons- 3115P c. the uranium isotope with 234 neutrons- 32692U d. the argon isotope with 22 neutrons- 4018Ar

For the types of radiation give, which of the following is the correct order of increasing ability to penetrate a piece of lead? a. alpha < gamma < beta b. alpha < beta < gamma c. beta < alpha < gamma d. beta < gamma < alpha e. gamma < alpha < beta

b An alpha particle has the lowest ability to penetrate a piece of lead. This knocks out choices C, D, & E. Gamma rays, being energy, will penetrate a piece of lead better than the other two types of radiation. Therefore, the answer is B.

Bromine has two major isotopes giving it an atomic mass of 79.904 amu. Based on this information, which of the following statements can explain the atomic mass value? a. The isotope Bromine-81 is more coming than Bromine-79. b. Bromine-79 and Bromine-81 exist in approximately equal proportions. c. Bromine 79 is about twice as abundant as Bromine-81. d. The two major isotopes of bromine have 45 and 46 neutrons.

b If the two isotopes of bromine are 79 and 81 and the reported atomic mass of bromine is almost 80, this means the two isotopes must be about equal in abundance because the average of 79 and 81 is 80.

What is the missing product in the nuclear reaction represented below? 25198Cf 2 10n + 13154Xe + _____ a. 11842Mo b. 11844Ru c. 12042Mo d. 12044Ru e. 12246Pd

b The equation 25198Cf 2 10n + 13154Xe + _____ can be rewritten as 25198Cf 10n + 10n + 13154Xe + _____ since there are TWO neutrons. The coefficient is what tells us there are 2 neutrons. To solve the equation, we need the mass number on each side of the arrow to total 251. On the product side we have 1+1+131 + x = 251. This means x is 118. The atomic number on each side of the arrow must equal 98. On the product side, we have 0+0+54+y=98. This means y = 44. The answer must be B.

Which part of Dalton's Theory of the Atom is not part of our atomic theory today? a. Atoms are rearranged in (chemical) reactions. b. All atoms of an element are exactly the same. c. Elements are combined in small whole number ratios (by mass) to form compounds. d. When comparing compounds with the same elements, the masses of the combined elements are in a small whole number ratio to each other.

b in a true chemical reaction, atoms are rearranged - they do not simply disappear or reappear. Elements are combined in small whole number ratios to form compounds, and they form small whole number ratios with each other when compounds that contain the same elements are compared. Atoms of the same element MUST have the same atomic number (number of protons). The number of neutrons can change, making the mass of the nucleus larger. This means atoms of one element (with neutral charge, meaning the number of electrons and protons are equal) can be different from each other in terms of neutrons.

Rutherford's gold foil experiment showed that the atom is mostly empty space because a. some of the alpha particles were reflected right back. b. some of the alpha particles were deflected. c. most of the alpha particles went straight through the foil. d. all of the alpha particles went straight through the foil. e. all of the alpha particles were deflected.

c Some of the particles reflected right back and some were deflected - but those prove that an atom has a tiny positive mass in the center. All of the particles did nothing. Most of the particles went through the foil - this means the atom is mainly empty space.

What do the following have in common? 20Ne 19F-1 24Mg+2 a. They are isotopes of each other. b. They are isomers of each other. c. They are isoelectronic with each other. d. They are different elements so they have nothing is common.

c They cannot be isotopes of each other because they are not the same elements. We do NOT know what an isomer is - while we know it has something to do with the 'same' we don't know WHAT is the same. We know that iso- means the same and electronic has to do with electrons. We can check to see if the electrons are the same for each atom or ion. Ne is an atom with 10 protons. This means it has 10 electrons . The fluoride ion has a negative charge - that means there are more electrons than protons. Since it is -1, there is only ONE more electron than protons, giving it 9 protons and 10 electrons. Mg has 12 protons, and a charge of +2. This means it has 2 fewer electrons than protons, giving it 10 electrons. ALL of the atoms and ions have TEN electrons - ISOELECTRONIC.

What are the mass numbers of the two isotopes of chlorine? a. 34.969 amu and 36.966 amu b. 34 and 36 c. 35 and 37 d. 17 and 17

c (graph)

if the abundance of 6Li (6.015 amu) is 7.50% and the abundance of 7Li (7.016 amu) is 92.50%, what is the average atomic mass? a. 6.075 amu b. 6.090 amu c. 6.923 amu d. 6.941 amu

d (6.015 × 7.50) + (7.016 × 92.50) = 6.941 100 Answers A & B can be crossed out. The natural abundance of Li is mainly Li-7, meaning the mass must be closer to 7 than 6. You have to divide by 100 because we are working with percentages.

Which is true of the 243Am+3 ion? a. 148 protons, 148 electrons, 243 neutrons b. 95 protons, 98 electrons, 243 neutrons c. 95 protons, 95 electrons, 148, neutrons d. 95 protons, 92 electrons, 148 neutrons

d The americium ion has a +3 charge. It has a mass number of 243. It has an atomic number of 95. It has 95 protons (eliminate A), {243-95} neutrons (eliminate B). If the charge is positive, it has fewer electrons than protons. This means it has 92 electrons. The answer must be D.

Which of the following represents a pair of isotopes? ZA a. I. II. 7 14 b. I. II. 14 14 c. I. II. 14 28 6 14 6 7 6 14 d. I. II. 7 14 7 13 e. I. II. 16 20

d in order for a pair of atoms to be isotopes, they must be the same element. In order for them to be the same element, they must have the same number of protons. If they have the same number of protons, they have the same atomic number. Atomic number is represented by Z.

Which scientist developed a model of the atom which he described as looking like 'plum pudding'? a. John Dalton b. Lord Kelvin c. Ernest Rutherford d. James Chadwick e. JJ Thomson

e John Dalton was the scientist that stated the first atomic theory in 1803; Lord Kelvin is the gentleman who stated a need for a temperature scale based on zero molecular motion. Chadwick discovered the neutron, and Rutherford did the Au foil experiment, proving the atom was mainly empty space with a positive center. This leaves Thomson, the gentleman who used a popular dessert to try to familiarize the masses with the atom.