Ionization Energy Trends and Influencing Factors | 电离能变化规律与影响因素

📚 Ionization Energy Trends and Influencing Factors | 电离能变化规律与影响因素

Ionization energy is a fundamental concept in chemistry that describes how tightly an atom holds its electrons. It is essential for understanding periodic trends, chemical reactivity, and the formation of ions.

电离能是化学中的基本概念，描述原子对其电子的束缚能力。它对于理解周期性规律、化学反应活性以及离子的形成至关重要。

1. Definition and Units | 定义与单位

The first ionization energy (I₁) is the energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous +1 cations.

第一电离能（I₁）是指从一摩尔气态原子中移走一摩尔电子，形成一摩尔气态+1阳离子所需的能量。

For element M, the process is represented as: M(g) → M⁺(g) + e⁻, with ΔH = +I₁ (always endothermic).

对于元素M，该过程可表示为：M(g) → M⁺(g) + e⁻，ΔH = +I₁（始终为吸热过程）。

Ionization energies are usually measured in kJ mol⁻¹. The greater the ionization energy, the more difficult it is to remove an electron.

电离能通常以 kJ mol⁻¹ 为单位。电离能越大，表示移走电子越困难。

---

2. Effective Nuclear Charge and Shielding Effects | 有效核电荷与屏蔽效应

The effective nuclear charge (Z_eff) is the net positive charge experienced by an outer electron. It equals the nuclear charge (Z) minus the shielding constant (S): Z_eff = Z − S.

有效核电荷（Z_eff）是外层电子实际感受到的净正电荷，等于核电荷（Z）减去屏蔽常数（S）：Z_eff = Z − S。

Inner electrons shield outer electrons from the full nuclear charge. As the number of inner shells increases, shielding becomes more effective, reducing Z_eff for the outer electron.

内层电子会屏蔽外层电子，使其感受不到全部核电荷。随着内层电子层数增多，屏蔽效应增强，从而降低外层电子的 Z_eff。

Across a period, Z increases and shielding remains roughly constant because electrons are added to the same shell. Hence Z_eff increases, pulling electrons closer and increasing ionization energy.

在同一周期中，Z增大而屏蔽效应大致不变，因为电子加在同一电子层。因此 Z_eff 增大，将电子拉得更近，电离能随之升高。

---

3. Atomic Radius and Ionization Energy | 原子半径与电离能

Atomic radius is inversely related to ionization energy. A smaller atomic radius means the outer electron is closer to the nucleus and experiences a stronger Coulombic attraction.

原子半径与电离能呈负相关。原子半径越小，外层电子离核越近，受到库仑吸引力越强。

As Z_eff increases across a period, the atomic radius decreases, and the first ionization energy generally increases.

同一周期中，Z_eff 增大导致原子半径减小，第一电离能总体上增大。

Down a group, atomic radius increases because additional electron shells are added. The outer electron is farther from the nucleus and more shielded, so ionization energy decreases.

同一族中，由于新增电子壳层，原子半径增大。外层电子离核更远且受到更多屏蔽，因此电离能减小。

---

4. General Trend Across a Period | 同周期变化规律

For elements in the same period, ionization energy generally increases from left to right, with occasional drops.

对于同一周期的元素，电离能总体从左到右增大，但存在个别下降。

For example, in the second period, Li has I₁ = 520 kJ mol⁻¹, while Ne has I₁ = 2081 kJ mol⁻¹. This reflects the increasing nuclear charge and decreasing atomic radius.

例如，在第二周期中，Li 的 I₁ 为 520 kJ mol⁻¹，而 Ne 的 I₁ 为 2081 kJ mol⁻¹。这反映了核电荷增大和原子半径减小。

The irregularity occurs at Be→B and N→O, which will be explained later by subshell stability.

Be→B 和 N→O 出现的突变，将在后文用亚层稳定性解释。

---

5. General Trend Down a Group | 同族变化规律

Down a group, ionization energy decreases. The added shells increase the distance between the nucleus and valence electrons, and the shielding effect becomes stronger.

同一族中，从上到下电离能减小。新增的电子层增加了核与价电子之间的距离，屏蔽效应也增强。

For instance, in Group 1: Li (520), Na (496), K (419), Rb (403), Cs (376) kJ mol⁻¹. The consistent decrease demonstrates the dominance of atomic size over nuclear charge.

例如，第1族中：Li（520）、Na（496）、K（419）、Rb（403）、Cs（376）kJ mol⁻¹。这种持续减小说明原子大小对电离能的影响超过核电荷的影响。

---

6. Half-filled and Fully-filled Subshell Stability | 半满与全满亚层的稳定性

Extra stability arises from half-filled and fully-filled subshells because of exchange energy and symmetry. This causes anomalies in the periodic trend.

半满和全满亚层因交换能和对称性而具有额外稳定性，导致周期性规律中出现异常。

In the second period, boron (2s²2p¹) has a lower I₁ than beryllium (2s²) because removing a p-electron leaves a stable 2s² configuration. In contrast, removing from Be would break the filled 2s².

在第二周期中，硼（2s²2p¹）的 I₁ 低于铍（2s²），因为移走一个p电子后留下稳定的 2s² 构型；而若移走铍的电子则会破坏满的 2s²。

Similarly, oxygen (2p⁴) has a lower I₁ than nitrogen (2p³). Removing an electron from O leaves a half-filled 2p³, while removing from N would disrupt the half-filled 2p³.

类似地，氧（2p⁴）的 I₁ 低于氮（2p³）。从氧移走一个电子后得到半满的 2p³，而从氮移走则会破坏半满的 2p³。

Other examples include Mg > Al and P > S in

Published by TutorHao | IB Chemistry Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）