principal energy level
⚛️ACS GENERAL CHEMISTRY STUDY GUIDE
Atomic and Electronic Structure for the ACS Exam
Review isotopes, photons, orbitals, electron configurations, periodic trends, and photoelectron spectra for ACS general chemistry.
8 key ideas8 flashcards5 practice questions
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Every electron has a shell, subshell, and orbital.
orbital family
two-electron capacity
Key ideas to know
Start with the relationships between ideas. Then close the notes and explain each one from memory.
- 01
Atomic number equals the number of protons in an atom's nucleus.
- 02
Isotopes of one element have the same proton count and different neutron counts.
- 03
A photon's energy equals Planck's constant multiplied by frequency.
- 04
Orbitals describe allowed electron probability distributions rather than fixed circular paths.
- 05
The Pauli rule permits at most two electrons per orbital with opposite spin.
- 06
Hund's rule places electrons singly in equal-energy orbitals before pairing.
- 07
Effective nuclear charge helps explain atomic radius and ionization-energy patterns across a period.
- 08
Photoelectron spectra connect binding energy and peak area with electron subshells and electron counts.
PART OF THE ACS GENERAL CHEMISTRY GUIDE
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Open the full ACS General Chemistry guide →Two ideas worth correcting now
NOT QUITE
→Electrons orbit the nucleus like planets
USE THIS INSTEAD
Orbitals describe probabilities from quantum mechanics, not classical tracks.
NOT QUITE
→A heavier isotope has more protons
USE THIS INSTEAD
Isotopes of one element differ in neutron count.
Flashcards
Answer before opening each card. The effort to retrieve is part of the learning.
1What identifies an element?Show answer ＋
Its number of protons.
2How do isotopes differ?Show answer ＋
They have different neutron counts and mass numbers.
3What is the relation between wavelength and frequency?Show answer ＋
Their product equals the speed of light in vacuum.
4How many electrons fit in one orbital?Show answer ＋
Two, with opposite spin.
5What is an orbital?Show answer ＋
A mathematical description of where an electron is likely to be found.
6Which electrons are removed first from a transition-metal cation?Show answer ＋
The electrons in the highest principal shell, commonly 4s before 3d.
7Why does atomic radius usually fall across a period?Show answer ＋
Rising effective nuclear attraction pulls electrons closer while they enter the same main shell.
8What does photoelectron peak area indicate?Show answer ＋
The relative number of electrons in a subshell.
Explain it in your own words
Use the answer as a check after you have written or spoken your response.
01How do you calculate average atomic mass?
Multiply each isotope mass by its fractional abundance, then add the products.
02Why is the first ionization energy of oxygen lower than nitrogen?
Oxygen pairs two electrons in one 2p orbital, adding repulsion that makes one easier to remove.
03How does a line spectrum form?
Electrons emit or absorb photons whose energies match gaps between allowed states.
04Why is a cation smaller than its neutral atom?
Electron loss reduces repulsion and can remove the outer shell, while nuclear charge stays the same.
05How can a photoelectron spectrum distinguish sodium from magnesium?
Magnesium has one more 3s electron and greater binding energies from its greater nuclear charge.
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