In Section 3.6, we estimated the effective nuclear charge on beryllium's valence electrons to be slightly greater than 2+. What would a similar treatment predict for the effective nuclear charge on boron's valence electrons? Would you expect the effective nuclear charge to be different for boron's 2s electrons compared to its 2p electron? In what way? (Hint: Consider the shape of the 2p orbital compared to that of the 2s orbital.)
Ch.9 - Periodic Properties of the Elements
Chapter 9, Problem 69a
Write the electron configuration for each ion. a. O2-

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Step 1: Identify the atomic number of the neutral atom. The atomic number of Oxygen (O) is 8, which means it has 8 electrons in its neutral state.
Step 2: Determine the number of electrons in the ion. The ion O<sup>2-</sup> has gained 2 electrons, so it has 10 electrons in total.
Step 3: Write the electron configuration for the neutral atom. The electron configuration for a neutral Oxygen atom is 1s<sup>2</sup> 2s<sup>2</sup> 2p<sup>4</sup>.
Step 4: Add the extra electrons to the electron configuration. The two extra electrons will fill up the 2p orbital, resulting in a 2p<sup>6</sup> configuration.
Step 5: Write the final electron configuration for the ion. The electron configuration for the O<sup>2-</sup> ion is 1s<sup>2</sup> 2s<sup>2</sup> 2p<sup>6</sup>.

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Electron Configuration
Electron configuration describes the distribution of electrons in an atom or ion's atomic orbitals. It is represented using a notation that indicates the energy levels and sublevels occupied by electrons. For example, the electron configuration of neutral oxygen (O) is 1s² 2s² 2p⁴, which shows how its electrons are arranged in different energy levels.
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Ionic Charge
Ionic charge refers to the electrical charge that an atom or molecule acquires when it gains or loses electrons. In the case of O²⁻, the oxygen atom has gained two additional electrons, resulting in a negative charge. This change in electron count alters the electron configuration, as the total number of electrons now exceeds the number of protons in the nucleus.
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Valence Electrons
Valence electrons are the outermost electrons of an atom and are crucial for determining its chemical properties and reactivity. For oxygen, the valence electrons are found in the second energy level (2s² 2p⁴). When forming ions, the gain or loss of valence electrons directly influences the atom's stability and its ability to bond with other elements.
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