Name: lattice energy patterns in ionic solids
Uploaded: 2020-09-03T13:38:28.000Z
Duration: 2 min 54 s
Channel: JoVE

K12 Standards

north-carolina-k-12-science-standard-course-of-study

North Carolina K-12 Science Standard Course of Study

9-12

Chemistry

Matter and its Interactions

PS.Chm.3.1

trends-in-lattice-energy-ion-size-and-charge

Trends in Lattice Energy: Ion Size and Charge

格子エネルギーは イオン性の格子の形成や 分離に関連しています しかし 塩化ナトリウムや 酸化マグネシウムが形成された時 その格子エネルギーは 大きく異なります イオン性化合物の格子エネルギー が異なるのはなぜでしょうか また どのような要因に 依存するのでしょうか イオン性化合物は 多数の荷電イオンが 静電相互作用によって 互いに引きつけ合って 整然と配置されています クーロンの法則によれば 2つのイオンの ポテンシャルエネルギーは イオン間の距離に反比例し イオン半径に依存します 周期表では アルカリ金属と アルカリ土類金属のイオン半径は 列の下に向かって大きくなります 金属イオンの 大きさが大きくなると イオン間の距離 すなわち結合長も 大きくなります 例えば 臭化リチウムと 臭化カリウムの結合長は それぞれ217pmと 282pmの間で異なります 核間距離が長くなると イオン間の引力が減少し イオンが分離しやすくなります このため 固体の 臭化リチウムを分離するための 格子エネルギーは 臭化カリウムの場合よりも大きく それぞれ807kJ/mol 対 682kJ/molとなりました イオン半径に加えて 格子エネルギーの大きさは イオン電荷にも依存します クーロンの法則によれば イオンのポテンシャルエネルギー は 電荷の積に正比例します ふっ化ナトリウムと 酸化カルシウムの2つの イオン性化合物を 考えてみましょう 両方の化合物の イオン距離は似ていますが 酸化カルシウムの 格子エネルギーは フッ化ナトリウムの約4倍です ナトリウムとフッ化物は どちらも一価イオンであり 電荷の積は1です しかし カルシウムイオンと 酸化カルシウムイオンは 2価のイオンであり 電荷の積は4であり フッ化ナトリウムの 4倍になります このため 酸化カルシウムを ガス状イオンに分離するのには フッ化ナトリウムに比べて 4倍近くの エネルギーが必要となります このように 格子エネルギーの大きさは イオンの電荷の積に正比例し イオン間の距離に反比例します

格子エネルギーの傾向：イオンの大きさ及び電荷

イオン化合物が安定しているのは、正イオンと負イオンの間に静電的な引力が働いているからです。化合物の格子エネルギーは、この引力の強さの尺度です。イオン性化合物の格子エネルギー(ΔHlattice)は、固体1モルを気体のイオンに分離するのに必要なエネルギーと定義されます。イオン性固体である塩化ナトリウムの場合、格子エネルギーはプロセスのエンタルピー変化です。 : 
 
 <img alt="Eq1" src="https://www.jovecore.com/CDNSource/lessons/1058/1058_Equations-01.png" style="height: 40px;" />
 
 <h4>慣例 </h4>
 
 ここでは、イオン性固体がイオンに分離されるという慣例を用いており、格子エネルギーは吸熱（正の値）となります。もう1つの方法は、同等でありながら反対の慣例を用いるもので、格子エネルギーは発熱性（負の値）であり、イオンが結合して格子を形成する際に放出されるエネルギーと表現されます。このように、他の文献で格子エネルギーを調べる際には、どちらの定義が使われているかを確認する必要があります。いずれの場合も、格子エネルギーの大きさが大きいほど、安定したイオン化合物であることを意味します。塩化ナトリウムの場合、ΔHlattice = 769 kJです。したがって、1モルの固体NaClをガス状のNa+とCl–イオンに分離するには769kJが必要です。1モルの気体のNa+とCl–イオンが固体のNaClになるとき、769kJの熱が放出されます。 
 
 <h4>クーロンの法則と格子エネルギー </h4>
 
 イオン結晶の格子エネルギーΔHlatticeは以下の式で表されます（電荷間の力を支配するクーロンの法則に由来）
 
 ΔHlattice =  C(Z +)(Z−)/Ro 
 
 ここで、Cは結晶構造の種類に依存する定数、Z+およびZ–はイオンの電荷、Roはイオン間距離（正負のイオンの半径の合計）です。このように、イオン結晶の格子エネルギーは、イオンの電荷が大きくなり、イオンの大きさが小さくなると、急激に大きくなります。他のパラメータがすべて一定の場合、陽イオンと陰イオンの両方の電荷を2倍にすると、格子エネルギーは4倍になります。
 
 <h4>例 </h4>
 
 <ol>
 <li>LiF (Z+ およびZ– = 1)の格子エネルギーは 1023 kJ/mol ですが、 MgO （(Z+ および Z– = 2)の格子エネルギーは 3900 kJ/mol です（ Ro はほぼ同じで、両方の化合物で約 200 pm ）。 </li>
 <li>原子間距離が異なると、格子エネルギーも異なります。例えば、MgF2の格子エネルギー(2957kJ/mol)とMgI2の格子エネルギー(2327kJ/mol)を比較すると、I-に比べてF-のイオンサイズが小さいことによる格子エネルギーへの影響がわかります。 </li>
 <li>貴重な宝石であるルビーは，微量のCr3+を含む酸化アルミニウム（Al2O3）です。この化合物Al2Se3は、一部の半導体デバイスの製造に使用されています。この2つのイオン化合物では、電荷Z+ とZ–が同じなので、格子エネルギーの違いはRoに依存します。O2–イオンはSe2–イオンよりも小さいので、Al2O3の方がイオン間距離が短く、そのため格子エネルギーが大きくなります。</li>
 <li>別の例として、酸化亜鉛（ZnO）とNaClを比較してみましょう。ZnOはNaClに比べてカチオンとアニオンのZ値が大きく、イオン間距離が小さいため、格子エネルギーが大きくなります。 </li>
 </ol>
 
 本書は <a href="https://openstax.org/books/chemistry-2e/pages/7-5-strengths-of-ionic-and-covalent-bonds">、 Openstax 、 Chemistry 2e 、 Section 7.5 ： Strengths of Ionic and Coalent Bonds から引用したものです。</a>

イオン性化合物は、その正イオンと負イオンの間の静電引力により安定しています。化合物の格子エネルギーは尺度です...

Education

JoVE Core

化学

Chemical Bonding: Basic Concepts

化学結合：基本概念

KEY TERMS AND CONCEPTS

主要用語と概念

lattice energy patterns in ionic solids

Lattice energy shows how strongly ions hold an ionic solid together. It is the energy required to separate one mole of a solid into its gaseous ions. For sodium chloride, this process requires 769 kJ per mole. The opposite convention may also be used, where lattice energy is the energy released when gaseous ions form the solid. In either case, a larger magnitude means a more stable ionic compound.

For ionic crystals, lattice energy follows a pattern based on charge and ion size. The relationship can be written as ΔH lattice = C(Z+)(Z−)/Ro. In this equation, C depends on the crystal structure, Z+ and Z− are the ion charges, and Ro is the distance between the ions. Because of this, lattice energy rises quickly when ion charges increase and when ion sizes decrease. If both ion charges double, the lattice energy becomes four times larger.

Examples show these trends clearly. LiF, with ion charges of 1 and 1, has a lattice energy of 1023 kJ/mol, while MgO, with charges of 2 and 2, has a lattice energy of 3900 kJ/mol. Their interionic distances are nearly the same, at about 200 pm. Ion size also matters. MgF2 has a lattice energy of 2957 kJ/mol, while MgI2 has a lower value of 2327 kJ/mol because F− is smaller than I−.

The same idea explains differences in other compounds. Ruby is aluminum oxide, Al2O3, and it contains traces of Cr3+. Al2Se3 is used in some semiconductor devices. These compounds have the same ion charges, so the difference in lattice energy depends on Ro. O2− is smaller than Se2−, so Al2O3 has the shorter interionic distance and the larger lattice energy. ZnO also has a larger lattice energy than NaCl because the ion charges are greater and the interionic distance is smaller.

Lattice Energy Patterns in Ionic Solids

types of chemical bonds

Chemical Bonding and Bond Properties

Chemical bonding explains how atoms and ions join to form molecules and compounds. American chemist Gilbert N. Lewis pioneered chemical bonding theory with the Lewis model. This model helps explain why bonds form, why some are stronger than others, and why compounds have fixed formulas like H2O instead of H4O. Ionic bonding involves ions, which are atoms or molecules with an electrical charge. A cation is a positive ion formed when a neutral atom loses one or more electrons from its valence...

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Valence Electrons, Lewis Symbols, and Bonding

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electronegativity

Electronegativity and Polar Bonds

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ionic bonding and electron transfer

Ionic Compounds and Crystal Lattices

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trends in lattice energy: ion size and charge

Lattice energy shows how strongly ions hold an ionic solid together. It is the energy required to separate one mole of a solid into its gaseous ions. For sodium chloride, this process requires 769 kJ per mole. The opposite convention may also be used, where lattice energy is the energy released when gaseous ions form the solid. In either case, a larger magnitude means a more stable ionic compound. For ionic crystals, lattice energy follows a pattern based on charge and ion size. The...

covalent bonding and lewis structures

Shared Electrons in Covalent Molecules

Covalent molecules form when atoms share electrons instead of transferring them. This bonding usually happens between nonmetal atoms with similar tendencies to attract electrons. Because the atoms pull on the electrons in a shared way, the bond is held together by mutual attraction. Covalent compounds often have physical properties that differ from ionic compounds. The attraction between neutral molecules is weaker than the attraction between charged ions. As a result, many covalent compounds...

bond polarity, dipole moment, and percent ionic character

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lewis structures of molecular compounds and polyatomic ions

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Drawing Lewis Structures with Valence Electron Counts

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resonance

Resonance Forms in Lewis Structures

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formal charges

Lewis Structures with Formal Charge

Lewis structures can sometimes show more than one reasonable arrangement for a molecule or polyatomic ion. Formal charge helps chemists choose the best Lewis structure when that happens. It is a useful way to compare possible structures in chemistry. Formal charge is the hypothetical charge an atom would have if bonding electrons were shared evenly between the atoms. It can also be found by starting with the valence electrons of the neutral atom, subtracting the nonbonding electrons, and then...

exceptions to the octet rule

Octet Rule Exceptions in Lewis Structures

Some covalent molecules do not follow the octet rule in their Lewis structures. Their central atoms can fall into three groups: odd-electron molecules, electron-deficient molecules, and hypervalent molecules. These cases show why a Lewis structure may not always give every atom eight valence electrons. Odd-electron molecules have an odd number of valence electrons, so one electron remains unpaired. Molecules with an odd number of electrons are called radicals. Nitric oxide, NO, is one example,...

bond energies and bond lengths

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bonding in metals

Electron Sea Model in Metals

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key terms and concepts

Learn how ion charge and ion size affect lattice energy in ionic solids, with examples like NaCl, LiF, MgO, MgF2, MgI2, Al2O3, and ZnO.

Lattice Energy Patterns in Ionic Solids | JoVE K12

chemistry

JoVE Core 化学は、簡潔で理解しやすいアニメーションビデオレッスンを使用して、一般的な化学の概念を生き生きとしたものにします。さらに、活動する科学者のビデオでは、現在世界中の実験室で行われている古典的そして独創的な研究・実験をお見せします。

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Ohio’s Learning Standards and Model Curriculum

Structure And Properties Of Matter

Chemical bonding

Tennessee Academic Standards

High School

Matter and Its Interactions

CHEM1.PS1.14

Virginia  Standards of Learning

HIgh School

CH.3

CH.3.d

Physics

PH.9

PH.9.e

Alabama Course of Study Science

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Motion and Stability: Forces and Interactions

9-12.C.2.2.b

Texas Essential Knowledge and Skills

Chemistry and Physics

IPC.7

IPC.7.A

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New York State Science Learning Standards

Physical Science

HS. Structure and Properties of Matter

HS-PS1-3.

HS. Chemical Reactions

HS-PS1-2.

HS-PS1-4.

HS-PS1-12.

Georgia Standards of Excellence

SC2.

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Bonding Types: From Nonpolar Covalent to Ionic

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PS.Chm.1.3

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	...

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Analyze and interpret data to explain the mechanisms and properties of the two main types of intramolecular (ionic and covalent) bonds.

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Lattice Energy Patterns in Ionic Solids

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