ANSWERS TO FIRST EXAM 10/10/10

1. ANSWERS TO FIRST EXAM 10/10/10 NOTE:, THE QUESTIONS AND ANSWERS ARE THE SAME FOR EACH EXAM FORM, HOWEVER THE ANSWER CHOICES ARE SCRAMBLED AND ARE DIFFERENTFOR EACH EXAM. YOU MUST COMPARE THE TEST ANSWER CHOICE TO THE ONE I PROVIDE ON THIS PPT. TO EXAMINE YOUR SCANTRON FOR MISGRADING ERRORS. All answers on this document are for choice one, however choice 2 answers are the same on a different choice.

2. Definition, atom is mainly empty space • Electron cloud : little mass in a large volume approximates empty space (very low density) 2) QUESTION ANALYSIS: EASY. Find protons in a potassium-42 nuc. ANSWER LOGIC: The proton number is the atomic number, from periodic table. For K the atomic number is 19, which is the number of protons and your answer. 3) QUESTION ANALYSIS: Some work, EASY. Find the numbers of neutrons and protons in both atoms and compare. ANSWER LOGIC: Write the n and p of both atoms and compareneed atomic numbers from periodic table PROTONS = 2 PROTONS = 3 Neutrons = 4-2 = 2Neutrons = 7-3 = 4 All choices refer to He-4, and He has one fewer proton than Li which eliminates choices B and C on form 1. He does not have one more neutron which eliminates choice A. He does have 2 less neutrons which is the answer. CHOICE D. 4 7 Li He 2 3

3. 4) QUESTION ANALYSIS: Some work, EASY. Find the numbers of electrons, neutrons and protons in both the oxygen -18 atom and (-2) ion, then compare. ANSWER LOGIC: Write the n and p AND ELECTRONS of both particles and compareneed atomic number from periodic table PROTONS = 8 PROTONS = 8 Neutrons = 18-8 = 10Neutrons = 18-8 = 10 Theanswer choices refer to the ion, which has 8 p, 10 n, 10 electrons NOTE: ionization does not affect the nucleus. 2-(indicative of 2 gained electrons) 2-6 8 ELECTRONS 2-8 10 ELECTRONS 18 18 O O 8 8

4. 5) For the number of valence electrons simply look up the configuration sequence for phosphorus (P) on the periodic table. The sequence is 2-8-5, with the last number (5 here) being the number of valence electrons, therefore the answer is 5 valence electrons. • 6) Any atom or ion emits its specific spectrum as electrons fallback to the ground state and release energy. The first fact in each answer choice refers to the gain or emission (loss) of energy. As electrons fall back they emit energy,,,eliminating the choices that indicate a gain. The correct answer is the one where the second fact indicates a return (fallback) to lower energy levels (stability). ANS: emit energy and return to lower energy levels. • 7) The word “atom” is indicative of the neutral ground state. In this state sodium has 11 electrons with an arrangement of 2-8-1 as found on the periodic table. Remember the periodic table gives only neutral ground state configurations. You could have derived this from Aufbau however you would use up more time than needed.

5. 8) QUESTION ANALYSIS: Some work, EASY. Find the numbers of neutrons and protons in both atoms and compare. ANSWER LOGIC: Write the n and p of both atoms and compareneed atomic numbers from periodic table PROTONS = 7 PROTONS = 8 Neutrons = 15-7 = 8Neutrons = 16-8 = 8 Simply subtract mass number from atomic number to get neutrons. Atomic numbers from periodic table and the question gave you the isotopic mass number. 15 16 N O 7 8 • 9) The nuclear charge is the atomic number, the nitrogen has atomic number, 7 and thus the greatest nuclear charge.

6. 10) The mass number of an element is the weighted average of the most abundant isotopes. The atomic mass number is usually closest to the most abundant isotope, in this case 35X is 90% abundant and thus the mass number will be closest to 35 amu. • 11) Facts: metals are toward the left of a period and nonmetals are toward the right. We also know that electronegativity and ionization energy INCREASE to the nonmetal right as radius decreases. Therefore the metals on the left have larger radii. • NOTE: the answer choices refer to the metals. 12) QUESTION ANALYSIS: Some work, EASY. ANSWER LOGIC: First write the configuration of the chlorine atom (neutral ground state), then add one electron from the ground for each – charge. Cl needs one more electron to complete a third shell octet therefore it will gain one to become a -1 ion. Because the negative ion has more electrons and a larger electron cloud…it will be larger. PROTONS=ELECTRONS = 17 PROTONS = 17, ELECTRONS =18 35 35 -1 Cl Cl 17 17

7. 13)FACTS, radius increasesdown a group and to the left of a period, find the sequence that follows that trend. Radius decreases up and to the right, another trend to look for. In this question look for increasing radii by finding a sequence of elements down a group or right to left across a period. The radius of F<Cl<Br<I is a sequence of increasing atomic radii as you read down the group #17( the halides). You could also look the radii up on table S, but this kills time bubbies. • 14) Nonmetals have high ionization energy, which eliminates the choices with low ionization energy for the first fact also nonmetals are poor conductors as they hold the electrons tightly (no mobile electrons in non metals). The answer is high ionization energy and poor electrical conductivity. NOTE the answer choices refer to nonmetals. • 15) The lowest ionization energy will be at the bottom of a group or to the left, usually a metal. Sr is the most bottom left of the choices and would have the lowest ionization energy. Looking o table S will give the same answer but will be time consuming. • 16) Group 18 (noble gasses) all have stable valence shells. He has a full first and all of the others have valence octets.

8. 17) Look for an excited state with 9 electrons (the atomic mass of Cl is 9, so 9 protons therefore 9 electrons). Also look for a configuration with 9 electrons that violates the Aufbau process. • This electron was promoted 18) QUESTION ANALYSIS: Some work, EASY. ANSWER LOGIC: Calculate the electron number by adding one electron to the ground state for each negative charge and removing from the ground state one electron for each positive charge. ATOM:PROTONS=ELECTRONS = 4ION:PROTONS= 4,ELECTRONS =2 +2 (2 lost electrons) 9 9 Be Be 4 4 2-2 atom has 2 more electrons 2

9. 19) During excitation the electron absorbs energy as it rises to a higher energy level, which excites and destabilizes it. No emission of light occurs during excitation. • 20) All elements in a group have identical valence configuration and valence electron number. For group 13 it is three electrons as the atoms all end in a three in the configuration sequence. • 21)As a group is read down, the radii increase (eliminates the choices that say decrease) and the ionization energies decrease. See notes • 22) All negative ions are larger than the neutral atom because they have more electrons and a larger cloud. Remember each – charge represents a gained electron. S-2 is larger and has 2. more electrons. • 23) The atom with the lowest ionization energy loses electrons most easily. You can look up ionization energies on table S (time intensive), or better use the trends. Ionization energy decreases down and to the left as is Rb relative to the other choices. Rb is the answer. Remember as ionization energy decreases the probability of removing an electron decreases.

10. 24)Elements that tend to gain electrons have high electronegativity and high ionization energy…both from strong effective nuclear charge. • 25) By definition non metals have higher electronegativities and higher ionization energies. Note the answer choices refer to non metals. • 26) The tendency of an atom to attract (and hold ) electrons is given by electronegativity. Look for the element closest to the right top of the periodic table. You could use table s also if you have the time. Nitrogen “N” is the answer. • 27) As you read down any group, the number of shells (principle quantum number) increases. • 28) An orbital is the most likely region of electron cloud probability. • 29) The lowest energy level is n=1, close to the nucleus.