Question

unit 3: atomic structure

1. if an atom has 23 electrons and an atomic mass of 51...

a) what is it’s atomic number?
b) what is it’s number of neutrons?
c) what element is it?
d) write the isotope symbol and isotope name for this atom.

1. calculate titanium’s weighted average atomic mass if it consists of 2 isotopes, ti-203 (29.52% abundance) and ti-205 (70.48% abundance). show all work including units.
2. draw a labeled picture of a fluorine atom showing all the following: protons, neutrons, electrons, s and p orbitals, energy levels.

Explanation:

Problem 16

Step1: Find atomic number

In a neutral atom, atomic number = number of electrons = 23

Step2: Calculate neutron count

Neutrons = Atomic mass - Atomic number = $51 - 23 = 28$

Step3: Identify element

Element with atomic number 23 is Vanadium

Step4: Write isotope details

Isotope symbol: $\ce{^{51}_{23}V}$, isotope name: Vanadium-51

Step1: Convert % to decimals

Ti-203: $29.52\% = 0.2952$; Ti-205: $70.48\% = 0.7048$

Step2: Calculate mass contributions

Ti-203: $203 \times 0.2952 = 60.0256$ amu
Ti-205: $205 \times 0.7048 = 144.484$ amu

Step3: Sum contributions

Weighted average = $60.0256 + 144.484 = 204.5096$ amu

Fluorine has an atomic number of 9 and atomic mass ~19, so it has 9 protons, 10 neutrons, and 9 electrons.

1. Nucleus (center): Labeled cluster of 9 protons (+ charge) and 10 neutrons (no charge).
2. Energy Level 1 (n=1): Contains 1 s-orbital (spherical) with 2 electrons. Label as "1s orbital (2 electrons)" and "Energy Level 1".
3. Energy Level 2 (n=2):

• 1 s-orbital (spherical) with 2 electrons, labeled "2s orbital (2 electrons)"
• 3 p-orbitals (dumbbell-shaped) with a total of 5 electrons (fill each p-orbital with 1 first, then pair), labeled "2p orbitals (5 electrons)"
• Label the whole outer shell as "Energy Level 2"

Answer:

a) 23
b) 28
c) Vanadium (V)
d) Isotope symbol: $\ce{^{51}_{23}V}$; Isotope name: Vanadium-51

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Problem 17