Chemistry - Electron Configurations - Quick Guides

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Study GuideChemistry–Electron Configurations1. Quiz: Valence Electrons1. QuestionValence electrons are located inAnswer Choices•energy levels closest to the nucleus•all energy levels•energy levels with the highest energyCorrect Answerenergy levels with the highest energyWhy This Is CorrectValence electrons are the electrons found in theoutermost energy levelof an atom, which is alsothehighest-energy energy level.These electrons are the most important because they:•Participate inchemical bonding•Determine an element’schemical reactivity•Explain why elements in the same group havesimilar properties2.QuestionWhen all the electrons in an atom are located in the lowest energy levels and sublevels, the electronsare

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Study GuideAnswer Choices•in an excited state•in the ground state•in a state of chaosCorrect Answerin the ground stateWhy This Is CorrectTheground stateis the lowest-energy, most stable arrangement of electrons in an atom.When electrons occupy the lowest possible energy levels and sublevels, the atom has minimumenergy.Anexcited stateoccurs only when one or more electrons absorb energy and move to higher energylevels.“State of chaos” is not a scientifically recognized term in atomic theory.3.QuestionWhich of the following elements would be expected to form an ion with a+1 charge?Answer Choices•Li: 1s² 2s¹•F: 1s² 2s² 2p⁵•Ne: 1s² 2s² 2p⁶Correct AnswerLi: 1s² 2s¹Why This Is CorrectLithium (Li) hasone valence electronin its outermost energy level (2s¹). To achieve a stable electronconfiguration, lithium tends tolose this one electron, forming a+1 ion (Li⁺).

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Study Guide•Lithium (Li)→ loses 1 electron →+1 charge•Fluorine (F)has 7 valence electrons and tends to gain 1 electron, forming a–1 ion•Neon (Ne)already has a full outer shell anddoes not usually form ionsTherefore,lithiumis the element expected to form an ion with a+1 charge.4.QuestionWhen forming a positive ion, electrons are lost from which level?Answer Choices•the level closest to the nucleus•the level farthest from the nucleus•any level within the electron cloudCorrect Answerthe level farthest from the nucleusWhy This Is CorrectWhen an atom forms apositive ion (cation), itloses electrons. Electrons are removed from theoutermost energy level, which is the levelfarthest from the nucleus.These outer electrons are:•held less tightly by the nucleus•higher in energy•easier to remove than inner (core) electronsRemoving inner electrons would require much more energy and usually does not happen in normalchemical reactions.Example:Sodium (Na) loses its single outer electron to form Na⁺, but its inner electrons remain unchanged.

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Study Guide5.QuestionWhich represents anexcited stateelectronic configuration of electrons?Answer Choices•1s² 2s² 2p¹•1s² 2s² 2p⁶ 3s¹•1s² 2s² 3s²Correct Answer1s² 2s² 3s²Why This Is CorrectAnexcited stateoccurs when one or more electrons absorb energy and move to ahigher energylevelinstead of filling the lowest possible levels first.•In1s² 2s² 3s², electrons occupy the3s orbital even though the 2p orbital is not filled.•This violates the Aufbau principle for ground states, indicating the atom is in anexcited state.Why the other options are NOT excited states:•1s² 2s² 2p¹→ Ground state (electrons fill lower energy orbitals first)•1s² 2s² 2p⁶ 3s¹→ Ground state (lowest-energy correct filling order)6. QuestionIsoelectronic ions are ions that haveAnswer Choices•different numbers of electrons•two extra electrons•the same number of electrons

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Study GuideCorrect Answerthe same number of electronsWhy This Is CorrectIsoelectronic ions are defined as ions (or atoms) that containthe same total number of electrons,even though they may be different elements or have different charges.For example:•Na⁺has 10 electrons•Ne has 10 electrons•F⁻has 10 electronsEven though their numbers of protons and charges differ, they areisoelectronicbecause theirelectron counts are identical.7.QuestionWhich electron configuration represents the fluoride ion,F⁻¹?Answer Choices•1s² 2s² 2p⁴•1s² 2s² 2p⁵•1s² 2s² 2p⁶Correct Answer1s² 2s² 2p⁶Why This Is CorrectA neutral fluorine atom has9 electronswith the configuration1s² 2s² 2p⁵.When fluorine forms thefluoride ion (F⁻), itgains one electron, giving it a total of10 electrons.That extra electron fills the 2p sublevel, resulting in the stable (noble gas–like) configuration:1s² 2s² 2p⁶This configuration matches the correct answer.

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Study Guide8. QuestionWhich electron configuration represents an atom with its electrons in theground state?Answer Choices•1 s² 2 s² 2 p⁵ 3 s¹•1 s² 2 s² 2 p⁵ 3 s²•1 s² 2 s² 2 p⁶ 3 s¹Correct Answer1 s² 2 s² 2 p⁶ 3 s¹Why This Is CorrectAn atom is in itsground statewhen all electrons occupy thelowest possible energy levelsbeforemoving to higher ones.•Electrons must completely fill lower-energy orbitals (like2p) before entering higher-energyorbitals (like3s).•In1 s² 2 s² 2 p⁶ 3 s¹, the 2p sublevel is fully filled, and only then does an electron occupy the3s sublevel.•This configuration follows theAufbau principle, so it represents the ground state.Why the Others Are Incorrect•1 s² 2 s² 2 p⁵ 3 s¹→ An electron is promoted to 3s before 2p is full →excited state•1 s² 2 s² 2 p⁵ 3 s²→ Still skips filling 2p completely →excited stateTherefore, the correct ground-state configuration is1 s² 2 s² 2 p⁶ 3 s¹.2. The Periodic TableThe periodic table is more than just a list of elements. Its layout shows us how electrons are arrangedin atoms. As we move across the table, electrons are added step by step into different energy levelscalledorbitalsorsubshells. Understanding this pattern helps us explain why elements behave theway they do.

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Study Guide2.1Filling of the s SubshellThe first two columns on theleft side of the periodic tableare called thealkali metals(Group 1)andalkaline earth metals(Group 2).As we move down these columns, electrons are added to thes subshell.•Group 1 elements have1 electron in the s subshell•Group 2 elements have2 electrons in the s subshellBecause these s electrons are loosely held, these elements easily lose them.That is why:•Group 1 elements usually form+1 ions•Group 2 elements usually form+2 ionsHeliumis an exception. Even though it has two s electrons, it is very stable and does not normallyreact.Figure1.Filling of thessubshells.2.2Filling of the 2p SubshellAfter the s subshell is filled, electrons begin to fill thep subshell.The elements fromboron (B) to neon (Ne)show how electrons fill the2p subshell.•The p subshell can holdup to 6 electrons•Each step across the table adds one more electron to the p subshellThese elements gradually become more stable as the p subshell fills.

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Study GuideFigure2.Filling of the 2psubshell.The same filling pattern repeats in the next energy level.Elements fromaluminum (Al) to argon (Ar)show the filling of the3p subshell.•Again, the p subshell fills from 1 to 6 electrons•When the 3p subshell is full, the atom becomes very stableFigure3. Filling of the 3p Subshell2.3Transition Metals and the 3d SubshellThe large block of metals in themiddle of the periodic tableare called thetransition metals.They extend fromscandium (21) to mercury (80).In these elements:•Electrons are added to thed subshell•The3d subshellcan holdup to 10 electronsAs you move across this block, the number of electrons in the 3d subshell increases gradually.Figure 4.Filling of the 3d subshell

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Study Guide2.4Anomalous Electron ConfigurationsSome elements do not follow the usual filling pattern.Chromium (Cr)andCopper (Cu)are important examples.•One electron moves from the4s subshellto the3d subshell•This happens because half-filled or fully filled d subshells are more stableBecause of this behavior:•Transition metals often havemultiple oxidation states•For example,vanadiumcan form +2, +3, +4, or +5 ionsThis reminds us that electron configurations haveexceptions, not just rules.2.5Lanthanides and ActinidesThe two rows shownat the bottom of the periodic tableare:•Lanthanides•ActinidesThey are placed separately to keep the table compact and easy to read.•Lanthanides: elements57–71•Actinides: elements89–103These elements involve the filling off subshells, which can hold14 electrons.Figure5.The correct placement of the lanthanides and actinides in the periodic table.

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Study Guide2.6Special Features of Actinides•Actinides havelarge, unstable nuclei•Many undergospontaneous radioactive decay•Elements with atomic numbers93 and higheraresynthetically produced2.7Why Electron Configuration MattersTheoutermost electronsof an atom are the most important.They determine:•Chemical behavior•Atomic size•Charge•Ability to form bondsWhen you understand how electrons fill subshells, the periodic table starts to make sense:•Elements in the same column behave similarly•This is because they have thesame type of outer electron configurationSummary•The periodic table shows how electrons fills, p, d, and f subshells•Electron arrangement explains chemical properties•Patterns exist, butexceptions are important•Knowing electron configuration helps you understand chemistry better3. Quiz: The Periodic Table1. QuestionAnother name for the lanthanide series is

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