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POGIL Answer Keys
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2. 2 / x Average Atomic Mass 12 24, 25, and 26
No, some have more mass that the others
Mass 24 – 16
Mass 25 – 2
Mass 26 – 2
5. 24Mg
6. Mass 24 – 8
Mass 25 – 1
Mass 26 – 1

3. 2 / x
7a. Mass 24 – 16
Mass 25 – 2
Mass 26 – 2
7b. It matches the model in Model 1
24 amu – as that has the greatest abundance 9a
9b. No
10a. It would be too much to squeeze into one box
10b. As the physical and chemical properties of isotopes are the same it is not usually important to scientists.

4. 2 / x 11. Mary’s method = 24.305 amu Jack’s method = 24.305 amu
Alan’s method = amu
12a. Mary and Jack
12b. Alan’s method incorrectly weights all the isotopes the same
amu
14a. 24Mg
14b. As 24Mg is the most abundant the weighted average will be closest to 24Mg
15. As the average mass is boron-11 must be most abundant.

5. 2 / x 16a. Yes 16b. No, as the composition is identical
16c. The bonding between the atoms makes the difference.
17. Allotrope – same composition, but different characteristics because of different bonding

6. 2 / x Coulombic Attraction + = proton, - = electron Attraction
As distance increases the force of attraction decreases.
Less than
Greater than
6a. The force of attraction
6b. The strength
7a. It increases
7b. In decreases
8. More protons make for a larger force
x 10-8 N
10. It should decrease

7. 2 / x
11. Row
12.
13. Chlorine
14a. No
14b. No
14c. Na = 11, Al = 13, Cl = 17
14d. Yes – more protons means more attraction
15a. Ca
15b. Cu
15c. Ar
16a. Li = 3, Na = 11, K = 19
16b. Distance as the force of attraction decreases while also having more protons

8. 2 / x
17a. Inverse
17b. Direct

9. 2 / x Electron Energy and Light Shades of the color Yes
Violet = highest
4. red = lowest
5a. Red
5b. Violet
5c. Wavelength is inversely related to frequency
6. There are lines that are different
Attract
Attraction, stonger
Gain
Lose

10. 2 / x 11. Absorbed to travel farther from the nucleus 12a. Picture B
12b. Releases
12c. Higher,
lower
12d. Released
13.

11. 2 / x
14a. n = 6 to n = 2
14b. The greater change in distance means the greater change in energy.
15. It only has 1 electron
16. Many, many H atoms each with their electrons making different transitions.
17a. n = 7, 6, 5, 4, 3, or 2 to n=1
17b. n = 7, 6, 5, or 4 to n = 3
18a. Li and Na are not present
18b. H and He are present
19. Emission and absorption spectrum would have lines at the same energies (wavelengths) but one is emitted lines (bright lines of color) and one absorbed lines (lines of black within the rainbow)

12. 2 / x Periodic Trends 1a. The first number 1b. pm
1c. The size of the atom (from center of nucleus to valence energy level)
2. Atomic radius increases
3. The atomic radius increases as the number of energy levels increases
4. Atomic radius decreases
5. The effective nuclear charge increases and pulls the electrons closer
6a. It takes energy to pull apart attracted particles
6b. Tight = more energy

13. 2 / x 7. Ionization energy decreases
8. The farther distance between the nucleus and the electrons means less energy needed to remove the electron.
9. Ionization energy increases
10. The greater effective nuclear charge requires more energy to remove electrons
11. Metals should have low ionization energy, so the electrons are easy to move allowing for high conductivity, malleability, and ductillity.
12. Diagram B

14. 2 / x 13a. Electronegativity decreases
13b. The increased distance means the nucleus of one atom is farther from the electrons of the other atom, so it has a weaker attraction.
13c. It increases
13d. The greater effective nuclear charge allows the nucleus to pull with greater attraction.
14. (on the left)= Electronegativity and I.E.
(on the right)= atomic radius

15. 2 / x 15a. Skip (IE of O is less than N) 15b. Skip
(Oxygen’s last electron is in an orbital already containing an electron, so the increase of electron-electron repulsion between the electrons make it easier to remove, even with more effective nuclear charge)
16. Ba, Fe, Br