Name: how ionic charge changes ion size
Uploaded: 2020-09-03T13:38:28.000Z
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Chemistry

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Ionic Radii

רדיוס יוני הוא רדיוס של קטיון או אניון, המוגדר לפי המרחק בין יונים בתרכובת יונית. קטיונים הם קטנים יותר מאטום האב ואילו אניונים גדולים ממנו. בדומה לרדיוסים אטומיים, רדיוסים יוניים נקבעים על ידי מספר האלקטרונים, האורביטלים המאכלסים את אלקטרוני הערכיות והמטען הגרעיני.כך לדוגמה ליתיום, שיש לו תצורת אלקטרונים של ליבת הליום ואלקטרון 2s הוא החיצוני ביותר. אלקטרון 2s ממוסך מפני המטען הגרעיני על ידי שני אלקטרוני 1s ותורם לרדיוס אטומי של 152 פיקומטרים. גריעת אלקטרון 2s החיצוני ביותר מייצרת קטיון ליתיום, שכולל פחות אלקטרונים אבל מספר זהה של פרוטונים לזה של האטום האב.שני אלקטרוני 1s מוחזקים קרוב יותר לגרעין מפני שהם חווים מטען גרעיני אפקטיבי גדול יותר מזה שחווה אלקטרון 2s. לכן, הרדיוס היוני של קטיון הליתיום הוא 60 פיקומטרים, קטן הרבה יותר מאטום האב. מגמה זו נצפית בדרך כלל בכל קטיוני המתכת ואטומי האב שלהם.לעומת זאת, אניונים הם גדולים יותר מאטומי האב שלהם. כשאטום פלואור מקבל אלקטרון, נוצרת תוספת של אלקטרון חיצוני ביותר, אבל מספר הפרוטונים, ומכאן המטען הגרעיני, לא משתנה. האלקטרון הנוסף יוצר דחייה בין אלקטרון לאלקטרון וגורם לאלקטרונים להתפשט יותר בחלל.לכן לאניון הפלואור יש רדיוס של 136 פיקומטרים, שהוא גדול הרבה יותר משל אטום האב. באופן כללי, הרדיוס היוני של יסודות בבלוקים s ו-p גדל במורד העמודה, ככל שגדל מספר רמות האנרגיה היסודיות ואיתו מספר האוריבטלים. מה קורה בקבוצת אטומים ויונים שיש בה מספר זהה של אלקטרונים?הם מכונים סדרה איזואלקטרונית"וניתן לארגן אותם לפי מספרים אטומיים עולים. לכל חבר בסדרה האיזואלקטרונית המתוארת יש 18 אלקטרונים. עם זאת, יש להם מספר אחר של פרוטונים.ליון הגופרית יש 16 פרוטונים המושכים 18 אלקטרונים, ואילו ליון הסידן 20 פרוטונים המושכים אותו מספר אלקטרונים. כיוון שיש לו יותר פרוטונים, סידן מושך אלקטרונים הרבה יותר קרוב לגרעין מכפי שגופרית יכולה למשוך, וכתוצאה מכך יון הסידן קטן יותר מיון הגופרית. ככל שהמטען הגרעיני גדול יותר, כך הרדיוס קטן יותר, אם כי הוספת אלקטרון קליפה משבשת את המגמה הזו.יחד עם זאת, הגופרית היא היון הגדול ביותר והסידן הוא היון הקטן ביותר בסדרה זו.

רדיוס יוני

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רדיוס יוני הוא המדד המשמש לתיאור גודלו של יון. לקטיון תמיד יש פחות אלקטרונים ומספר פרוטונים זהה לזה של אטום האב; הוא קטן יותר מהאטום ממנו הוא נגזר. לדוגמה, הרדיוס הקוולנטי של אטום אלומיניום (1s22s22p63s23p1) הוא 118 pm, ואילו הרדיוס היוני של Al3+ (1s22s22p6) הוא 68 pm. כאשר אלקטרונים מוסרים מקליפת הערכיות החיצונית, אלקטרוני הגרעין הנותרים התופסים קליפות קטנות יותר חווים מטען גרעיני אפקטיבי יותר "Zeff" ונמשכים עוד יותר לגרעין. 

קטיונים בעלי מטענים גדולים יותר קטנים מקטיונים בעלי מטענים קטנים יותר (לדוגמה, ל-V2+ יש רדיוס יוני של 79 pm, בעוד של V3+ הוא 64 pm). בהמשך לקבוצות של הטבלה המחזורית, לקטיונים של יסודות עוקבים בעלי אותו מטען יש בדרך כלל רדיוסים גדולים יותר, המקבילים לעלייה במספר הקוונטי העיקרי, n. 

אניון (יון שלילי) נוצר על ידי הוספת אלקטרונים אחד או יותר לקליפת הערכיות של האטום. זה גורם לדחייה גדולה יותר בין האלקטרונים וירידה ב"Zeff" לכל אלקטרון. שתי ההשפעות (המספר המוגבר של האלקטרונים והקטנת Zeff) גורמות לרדיוס של אניון להיות גדול יותר מזה של אטום האב. לדוגמה, לאטום גופרית ([Ne]3s23p4) יש רדיוס קוולנטי של 104 pm, בעוד שהרדיוס היוני של האניון הגופרתי ([Ne]3s23p6) הוא 170 pm. עבור יסודות עוקבים שממשיכים לרדת בכל קבוצה, לאניונים יש מספרים קוונטיים עיקריים גדולים יותר, ולכן, רדיוסים גדולים יותר. 

אומרים כי אטומים ויונים בעלי אותה תצורת אלקטרונים הם איזואלקטרוניים. דוגמאות למינים איזואלקטרוניים הם N3–, O2–, F–, Ne, Na+, Mg2+ ו- Al3+ (1s22s22p6). סדרה איזואלקטרונית נוספת היא P3–, S2–, Cl–, Ar, K+, Ca2+ ו-Sc3+ ([Ne]3s23p6). עבור אטומים או יונים שהם איזואלקטרוניים, מספר הפרוטונים קובע את הגודל. ככל שהמטען הגרעיני גדול יותר, כך הרדיוס קטן יותר בסדרה של יונים ואטומים איזואלקטרוניים. 

טקסט זה מותאם מ <a href="https://openstax.org/books/chemistry-2e/pages/6-5-periodic-variations-in-element-properties">OpenStax Chemistry 2e, Section 6.5: Periodic Variations in Element Properties.</a></div>

רדיוס יוני הוא המדד המשמש לתיאור גודלו של יון. לקטיון יש תמיד פחות אלקטרונים ואותו מספר פרוטונים כמו לאטום האב; הוא...

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Periodic Properties of the Elements

תכונות מחזוריות של היסודות

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how ionic charge changes ion size

Ionic radius describes the size of an ion. It changes when an atom gains or loses electrons. Cations are positive ions with fewer electrons than the parent atom, and they are smaller than the atoms they come from.

Aluminum shows this pattern clearly. A neutral aluminum atom has a covalent radius of 118 pm, while Al3+ has an ionic radius of 68 pm. When electrons are removed from the outer valence shell, the remaining core electrons feel a stronger effective nuclear charge, or Zeff. That pull draws them closer to the nucleus.

Cations with larger charges are usually smaller than cations with smaller charges. For example, V2+ has an ionic radius of 79 pm, while V3+ is smaller at 64 pm. Moving down a group in the periodic table, cations with the same charge generally get larger. This happens because the principal quantum number, n, increases.

Anions are negative ions formed when one or more electrons are added to the valence shell. Extra electrons increase electron repulsion and reduce Zeff per electron. Both effects make an anion larger than its parent atom. Sulfur is an example: a sulfur atom has a covalent radius of 104 pm, while the sulfide anion has an ionic radius of 170 pm. Anions also tend to have larger radii down a group because n increases.

Atoms and ions with the same electron configuration are called isoelectronic. One example set is N3−, O2−, F−, Ne, Na+, Mg2+, and Al3+, which all have the same electron arrangement. Another is P3−, S2−, Cl−, Ar, K+, Ca2+, and Sc3+. In an isoelectronic series, the number of protons controls size. The greater the nuclear charge, the smaller the radius.

How Ionic Charge Changes Ion Size

periodic classification of the elements

How Valence Electrons Shape the Periodic Table

The periodic table organizes elements by increasing atomic number, and it also shows why elements in the same group behave alike. As the electron configurations are placed into the table, a repeating pattern appears in the outer shells of atoms. These outer electrons are called valence electrons, and they play the biggest role in chemical reactions. They are the highest-energy electrons in an atom, so they are easier to lose or share than core electrons. Valence electrons also help determine...

ionization energy

Ionization Energy Trends in the Periodic Table

Ionization energy is the energy needed to remove an electron from a gaseous atom or ion in its ground state. The first ionization energy, or IE1, removes the most loosely bound electron and forms a 1+ cation. The second ionization energy, IE2, removes the next electron, and each later ionization energy removes another electron from the atom or ion. Ionization always requires energy, so these processes are endothermic. That means ionization energy values are always positive. In general, larger...

atomic radii and effective nuclear charge

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Periodic Trends in Atomic Size

Periodic trends in atomic size help explain why atoms get larger or smaller across the periodic table. Elements in the same group show similar chemical behavior because they have the same number and arrangement of valence electrons. Across a period, each new element adds one proton to the nucleus and one electron to the valence shell. Down a group, the number of valence electrons stays the same, but the principal quantum number increases by one. Atomic radius is not easy to define with perfect...

ionic radii

Ionic radius describes the size of an ion. It changes when an atom gains or loses electrons. Cations are positive ions with fewer electrons than the parent atom, and they are smaller than the atoms they come from. Aluminum shows this pattern clearly. A neutral aluminum atom has a covalent radius of 118 pm, while Al3+ has an ionic radius of 68 pm. When electrons are removed from the outer valence shell, the remaining core electrons feel a stronger effective nuclear charge, or Zeff. That pull...

electron affinity

Electron Affinity Trends on the Periodic Table

Electron affinity is the energy change that happens when a gaseous atom gains an electron and becomes a negative ion, or anion. For many elements, this process releases energy, so the electron affinity value is negative. For some elements, energy must be added instead, so the value is positive. Electron affinity also applies when more than one electron is added. The second electron affinity is the energy change for adding an electron to an anion to make a 2− ion. Later electron affinities...

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Alkali Metals: Reactivity Trends

Alkali metals are Group 1 elements with one valence electron. They are soft, shiny metallic solids that are malleable, ductile, and good conductors of heat and electricity. Their melting points are unusually low for metals and drop as you move down the group. Density generally increases down the group, except for potassium. The trend in atomic size helps explain their behavior. Moving from lithium to cesium, each element has a higher principal quantum number, so the outer electron is farther...

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Halogens: Trends and Reactions

Halogens are Group 17 nonmetals that show clear trends in structure and reactivity. At room temperature, fluorine and chlorine are gases, bromine is a liquid, and iodine is a solid. Astatine is highly unstable and radioactive, so most of its properties are still unknown because it has a very short half-life. Tennessine is a synthetic element that is also predicted to belong to this group. These elements do not usually exist as single atoms. Instead, they form diatomic molecules, which means...

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Noble Gases: Sources, Uses, and Reactions

Noble gases are the group 18 elements helium, neon, argon, krypton, xenon, and radon. They were called “noble” because they were once thought to be nonreactive. That idea changed in 1962, when Dr. Neil Bartlett at the University of British Columbia showed that this assumption was not fully correct. These gases occur in very small amounts in the atmosphere. Some natural gas contains 1–2% helium by mass. Helium is separated from natural gas by removing the condensable components, which leaves...

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Learn how cations and anions change size, why ionic radius varies with charge, and how isoelectronic species compare across the periodic table.

How Ionic Charge Changes Ion Size | JoVE K12

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Periodic Table Trends: Atomic Radii, Ionization, and Electronegativity

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Electron Configuration of Multielectron Atoms

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Periodic Classification of the Elements

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The Periodic Table

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Atomic Mass

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Molar Mass

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Use the Periodic Table as a model to predict the relative properties of elements based on the pattern of valence electrons in the outermost energy levels of atoms.

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Atomic Radii and Effective Nuclear Charge

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Electron Affinity

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This process can be either ...

Construct an explanation to infer the atomic size, reactivity, electronegativity, and ionization energy of an element based on its position in the Periodic Table.

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Lewis Structures of Molecular Compounds and Polyatomic Ions

To draw Lewis structures for complicated molecules and molecular ions, it is helpful to follow a step-by-step procedure as outlined:


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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.

PS.Chm.3.1

Analyze the structure of atoms and isotopes.

How Ionic Charge Changes Ion Size

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