Question

Write the condensed electron configurations for the following atoms, using the appropriate noble-gas core abbreviations: (a) \(\mathrm{Cs},(\mathbf{b}) \mathrm{Ni},(\mathbf{c}) \mathrm{Se},(\mathbf{d}) \mathrm{Cd},(\mathbf{e}) \mathrm{U},(\mathbf{f}) \mathrm{Pb}\)

Short answer

The condensed electron configurations for the given atoms are: (a) Cesium (Cs): \([Xe]6s^1\) (b) Nickel (Ni): \([Ar]4s^2 3d^8\) (c) Selenium (Se): \([Ar]4s^2 3d^{10} 4p^4\) (d) Cadmium (Cd): \([Kr]5s^2 4d^{10}\) (e) Uranium (U): \([Rn]7s^2 5f^3 6d^1\) (f) Lead (Pb): \([Xe]6s^2 4f^{14} 5d^{10} 6p^2\)

Step-by-step solution

(a) Cs (Cesium) Electron Configuration

: To find the condensed electron configuration of Cesium: 1. Identify the noble gas that comes before Cs: The noble gas before Cs is Xenon (Xe) with an atomic number of 54. 2. Write down the noble-gas core abbreviation: [Xe] 3. Add the electron configuration for Cs after the noble gas abbreviation: Cs has an atomic number of 55. The electron configuration after Xe is 6s1. So, the condensed electron configuration for Cesium is: \([Xe]6s^1\)

(b) Ni (Nickel) Electron Configuration

: To find the condensed electron configuration of Nickel: 1. Identify the noble gas that comes before Ni: The noble gas before Ni is Argon (Ar) with an atomic number of 18. 2. Write down the noble-gas core abbreviation: [Ar] 3. Add the electron configuration for Ni after the noble gas abbreviation: Ni has an atomic number of 28. The electron configuration after Ar is 4s2 3d8. So, the condensed electron configuration for Nickel is: \([Ar]4s^2 3d^8\)

(c) Se (Selenium) Electron Configuration

: To find the condensed electron configuration of Selenium: 1. Identify the noble gas that comes before Se: The noble gas before Se is Argon (Ar) with an atomic number of 18. 2. Write down the noble-gas core abbreviation: [Ar] 3. Add the electron configuration for Se after the noble gas abbreviation: Se has an atomic number of 34. The electron configuration after Ar is 4s2 3d10 4p4. So, the condensed electron configuration for Selenium is: \([Ar]4s^2 3d^{10} 4p^4\)

(d) Cd (Cadmium) Electron Configuration

: To find the condensed electron configuration of Cadmium: 1. Identify the noble gas that comes before Cd: The noble gas before Cd is Krypton (Kr) with an atomic number of 36. 2. Write down the noble-gas core abbreviation: [Kr] 3. Add the electron configuration for Cd after the noble gas abbreviation: Cd has an atomic number of 48. The electron configuration after Kr is 5s2 4d10. So, the condensed electron configuration for Cadmium is: \([Kr]5s^2 4d^{10}\)

(e) U (Uranium) Electron Configuration

: To find the condensed electron configuration of Uranium: 1. Identify the noble gas that comes before U: The noble gas before U is Radon (Rn) with an atomic number of 86. 2. Write down the noble-gas core abbreviation: [Rn] 3. Add the electron configuration for U after the noble gas abbreviation: U has an atomic number of 92. The electron configuration after Rn is 7s2 5f3 6d1. So, the condensed electron configuration for Uranium is: \([Rn]7s^2 5f^3 6d^1\)

(f) Pb (Lead) Electron Configuration

: To find the condensed electron configuration of Lead: 1. Identify the noble gas that comes before Pb: The noble gas before Pb is Xenon (Xe) with an atomic number of 54. 2. Write down the noble-gas core abbreviation: [Xe] 3. Add the electron configuration for Pb after the noble gas abbreviation: Pb has an atomic number of 82. The electron configuration after Xe is 6s2 4f14 5d10 6p2. So, the condensed electron configuration for Lead is: \([Xe]6s^2 4f^{14} 5d^{10} 6p^2\)

Key concepts

Condensed Electron Configuration

Condensed electron configuration is a simplified way to express the arrangement of electrons in an atom. This involves using the noble gas that directly precedes the element in the periodic table to represent a core set of electrons. By doing so, it provides a clear and concise way to depict the gain, loss, or sharing of electrons during chemical reactions.

The condensed electron configuration comprises two parts:

• Noble Gas Core: which indicates the electron configuration of the noble gas.
• Valence Electron Configuration: which shows the outermost electrons added after the noble gas core.

For example, to write the condensed electron configuration for cesium (Cs), we first locate cesium on the periodic table. Xenon (Xe) is the noble gas that comes right before cesium. Therefore, the electron configuration can be represented as \([Xe]6s^1\). This indicates that after filling the electron configuration up to the xenon core, only one electron remains in the 6s orbital. Remember, this method provides clarity and reduces transcription errors when writing long electron configurations.

Noble Gas Abbreviation

The noble gas abbreviation is a shortcut technique in electron configuration that uses the electron arrangement of the nearest noble gas to simplify the representation of an atom's electron configuration. Noble gases like helium, neon, or argon have stable electron configurations, which are usually complete octets, providing a reference point for core electrons.

Here is a step-by-step explanation of using the noble gas abbreviation:

• Identify the element for which you want the electron configuration.
• Find the noble gas just before this element in the periodic table.
• Use the symbol of the noble gas in brackets [like this] to represent the electron configuration up to that point.
• Add on the remaining electrons for the element, detailing the orbitals filled beyond the noble gas core.

For nickel (Ni), the nearest preceding noble gas is argon (Ar). Hence, the noble gas abbreviation is expressed as \([Ar]4s^2 3d^8\), after recognizing argon's full electron configuration comprises part of nickel's configuration. This abbreviation is a crucial tool for chemists that ensures clarity and efficiency when dealing with complex atomic structures.

Atomic Structure

Understanding the atomic structure is key to grasping chemistry principles. Atoms, the basic units of matter, are composed of protons, neutrons, and electrons. Electrons arrange around the nucleus, taking specific patterns defined by electron configuration rules.

Four primary concepts govern electron configuration:

• Shells and Subshells: Electrons occupy orbitals within shells and subshells. These orbitals can hold a defined number of electrons and are denoted by letters like s, p, d, and f.
• Aufbau Principle: This principle outlines that electrons fill orbitals starting from those with the lowest energy and progressing upwards.
• Pauli Exclusion Principle: No two electrons in an atom can have the same set of four quantum numbers, meaning each orbital holds a maximum of two electrons with opposite spins.
• Hund's Rule: Electrons will fill degenerate orbitals singly and with parallel spins before pairing.

Applying these principles allows us to derive the electron configurations of various elements and predict their chemical properties. Atomic structure plays a fundamental role in chemistry, helping us interpret the behavior of atoms in molecules and compounds.