Question

1. what is the molar mass of cf₄?

a. 86.0 g cf₄
b. 87.0 g cf₄
c. 88.0 g cf₄
d. 89.0 g cf₄

1. what group of elements is used for the \short - cut, or abbreviated\ method of electron configurations?

a. s - block elements
b. p - block elements
c. noble gases
d. transition metals
isotope data

isotope	percent abundance	mass (amu)
2	29.6	55.0
3	60.1	56.0

1. use the information in the isotope data table to calculate the average atomic mass of the element.

a. 53.0 amu
b. 55.5 amu
c. 554.98 amu
d. 5549.8 amu

1. what is the identity of the element based on the isotope data table?

a. cr
b. fe
c. co
d. ni

1. for an electron in an atom to change from the ground state (lower energy level) to an excited state (higher energy level),

a. energy must be released.
b. energy must be absorbed.
c. radiation must be emitted.
d. the electron must make a transition from a higher to a lower energy level.

1. which coefficients correctly balance the chemical equation: cao + h₂o → ca(oh)₂

a. 2, 1, 2
b. 1, 2, 3
c. 1, 2, 1
d. 1, 1, 1

1. as you move down a group, the trend in atomic radii is caused by

a. no increase in number of occupied energy levels.
b. an increase in number of occupied energy levels.
c. atomic radii does not change down a group.
d. an increase in the number of unoccupied energy levels.
e. no increase in the number of unoccupied energy levels.

Explanation:

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Question 16

Step1: Find atomic masses

Atomic mass of C = $12.0$ amu, F = $19.0$ amu.

Step2: Calculate molar mass

$M = 12.0 + 4\times19.0 = 88.0$ g $\text{CF}_4$

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Question17

Step1: Recall shortcut config rule

Abbreviated electron config uses prior noble gas core.

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Question18

Step1: Convert % to decimals

$10.3\%=0.103$, $29.6\%=0.296$, $60.1\%=0.601$

Step2: Weighted average calculation

$$\begin{align*} \text{Mass} &= (0.103\times54.0) + (0.296\times55.0) + (0.601\times56.0) \\ &= 5.562 + 16.28 + 33.656 \\ &= 55.498 \approx 55.5 \end{align*}$$

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Question19

Step1: Match mass to element

Average mass ~55.5 amu matches Fe (Iron, ~55.85 amu, closest fit).

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Question20

Step1: Recall electron energy rules

Ground to excited state requires energy absorption.

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Question21

Step1: Count atoms on each side

Left: 1 Ca, 2 O, 2 H; Right: 1 Ca, 2 O, 2 H. Equation is already balanced.

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Question22

Step1: Recall atomic radius trend

Down a group, occupied energy levels increase, expanding atomic radii.

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Answer:

1. c. 88.0 g $\text{CF}_4$
2. c. noble gases
3. b. 55.5 amu
4. b. Fe
5. b. Energy must be absorbed.
6. d. 1, 1, 1
7. b. an increase in number of occupied energy levels.