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Atomic Structure Flashcards

Atomic structure covers the composition of atoms, electron configurations, quantum mechanical models, and periodic trends. This topic explores how protons, neutrons, and electrons are arranged and how atomic properties like ionization energy and electronegativity vary across the periodic table.

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What three subatomic particles make up an atom?

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Protons (positive, in nucleus), neutrons (neutral, in nucleus), and electrons (negative, in orbitals around nucleus).

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What defines the atomic number of an element?

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The number of protons in the nucleus. It determines the element's identity and position on the periodic table.

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What are isotopes?

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Atoms of the same element with the same number of protons but different numbers of neutrons, giving them different mass numbers.

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What are the four quantum numbers?

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Principal (n), angular momentum (l), magnetic (ml), and spin (ms). Together they describe the state of an electron in an atom.

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What does the principal quantum number (n) indicate?

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The energy level and relative size of the orbital. It takes positive integer values (1, 2, 3, ...).

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What values can the angular momentum quantum number (l) take?

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Integer values from 0 to n-1. Values 0, 1, 2, 3 correspond to s, p, d, f subshells respectively.

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State the Aufbau principle.

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Electrons fill orbitals starting from the lowest energy level to the highest (1s, 2s, 2p, 3s, 3p, 4s, 3d, ...).

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State Hund's rule.

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Electrons occupy degenerate orbitals singly with parallel spins before pairing up in the same orbital.

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State the Pauli exclusion principle.

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No two electrons in an atom can have the same set of four quantum numbers. Each orbital holds a maximum of two electrons with opposite spins.

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Write the electron configuration of Fe (Z = 26).

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1s2 2s2 2p6 3s2 3p6 4s2 3d6. Note: the Fe2+ ion loses the 4s electrons first, becoming [Ar] 3d6.

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Why are Cr and Cu exceptions to the expected electron configuration?

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A half-filled (Cr: [Ar] 3d5 4s1) or fully filled (Cu: [Ar] 3d10 4s1) d subshell provides extra stability due to exchange energy.

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How does ionization energy trend across a period and down a group?

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Increases across a period (greater nuclear charge) and decreases down a group (larger atomic radius, more shielding).

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How does atomic radius trend across a period and down a group?

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Decreases across a period (increasing effective nuclear charge) and increases down a group (additional electron shells).

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How does electronegativity trend across the periodic table?

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Increases across a period and decreases down a group. Fluorine is the most electronegative element.

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What is effective nuclear charge (Zeff)?

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The net positive charge experienced by valence electrons after accounting for shielding by inner electrons. Zeff = Z - S (Slater's rules).

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What is electron affinity?

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The energy change when a gaseous atom gains an electron. Generally becomes more negative (exothermic) across a period from left to right.

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What does the photoelectron spectrum (PES) reveal about an atom?

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The number and binding energies of electrons in each subshell. Peak height indicates relative number of electrons; position indicates binding energy.

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What is Coulomb's law and how does it apply to atomic structure?

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F = kq1q2/r2. Greater nuclear charge and smaller radius increase attraction between the nucleus and electrons, raising ionization energy.

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Why do elements in the same group have similar chemical properties?

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They have the same valence electron configuration, so they form similar types and numbers of bonds and undergo analogous reactions.

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Study Tips for Atomic Structure

1

Memorize the orbital filling order using the diagonal rule diagram: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, and so on.

2

Practice writing electron configurations for transition metals and their ions, paying special attention to the Cr and Cu exceptions.

3

Link each periodic trend (radius, ionization energy, electronegativity) back to effective nuclear charge and shielding to build a unified mental model.

4

Use photoelectron spectrum data to verify your electron configurations; peak heights should match the number of electrons you predict in each subshell.

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