Question

lohse, chem 181
exam 1 review: subatomic structure
names:
please answer the following questions in small groups. in 25 min, we will break out and discuss our answers
element | boron (b) | nickel (ni) | krypton (kr) | fluorine (f)
atomic number (z) | 5 | | |
mass number (a) | 79 | 65 | |

of neutrons | | 37 | 48 | 19

of protons | | | |

of electrons (assume a neutral atom) | | | 36 | 9

what is the molar mass (mw) of your element? (include units)

Explanation:

Step1: Recall key atomic relationships

For neutral atoms:

1. Atomic Number (Z) = # of protons = # of electrons
2. Mass Number (A) = # of protons + # of neutrons, so # of neutrons = A - Z

Step2: Fill in Boron's missing values

Substep2a: Calculate # of protons

Atomic Number (Z) = 5, so # of protons = 5

Substep2b: Calculate # of neutrons

$\text{# of neutrons} = A - Z = 79 - 5 = 74$

Substep2c: Calculate # of electrons (neutral atom)

of electrons = # of protons = 5

Step3: Fill in Nickel's missing values

Substep3a: Calculate # of protons

$\text{# of protons} = A - \text{# of neutrons} = 65 - 37 = 28$

Substep3b: Identify Atomic Number (Z)

Atomic Number (Z) = # of protons = 28

Substep3c: Calculate # of electrons (neutral atom)

of electrons = # of protons = 28

Step4: Fill in Krypton's missing values

Substep4a: Identify # of protons

of protons = # of electrons (neutral) = 36

Substep4b: Identify Atomic Number (Z)

Atomic Number (Z) = # of protons = 36

Substep4c: Calculate Mass Number (A)

$A = \text{# of protons} + \text{# of neutrons} = 36 + 48 = 84$

Step5: Fill in Fluorine's missing values

Substep5a: Identify # of protons

of protons = # of electrons (neutral) = 9

Substep5b: Identify Atomic Number (Z)

Atomic Number (Z) = # of protons = 9

Substep5c: Calculate Mass Number (A)

$A = \text{# of protons} + \text{# of neutrons} = 9 + 19 = 28$

Step6: Determine molar masses

Molar mass of an element (for the given isotope) equals its mass number, with units g/mol.

Answer:

Completed Table:

Element	Boron (B)	Nickel (Ni)	Krypton (Kr)	Fluorine (F)
Mass Number (A)	79	65	84	28
# of neutrons	74	37	48	19
# of protons	5	28	36	9
# of electrons (neutral atom)	5	28	36	9

Molar Masses:

• Boron (given isotope): 79 g/mol
• Nickel (given isotope): 65 g/mol
• Krypton (given isotope): 84 g/mol
• Fluorine (given isotope): 28 g/mol