Name: electron affinity trends on the periodic table
Uploaded: 2020-09-03T13:38:28.000Z
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Electron Affinity

عندما إضافة إلكترون إلى ذرة غازية،لوحظ تغيير في الطاقة،يسمى تقارب الالكترون. يقيس تقارب الإلكترون سهولة اكتساب الذرة للإلكترون. على سبيل المثال،تقارب الإلكترون للكلور هو 348.6 كيلوجول لكل مول.تشير العلامة السالبة إلى أنه تغيير طارد للحرارة. ومع ذلك،فإن الأرجون لديه تقارب للإلكترون موجب،مشيرا إلى أنّتشكيل أنيون الأرجون يتطلب توفير الطاقة. بشكل عام،كلما زادت الجاذبية بين ذرة وإلكترون مضاف،كلما كان تقارب الإلكترون أكثر سالبية.تقارب الإلكترون،على غرار طاقات التأين،تظهر الاتجاهات في الجدول الدوري. بالتحرك أسفل المجموعة 1،الحجم الذري يزداد كلما احتلت الإلكترونات أعداداًكمية أساسية أعلى. لذلك،فإن الإلكترونات الواردة تمر بجاذبية نووية أقل،تؤدي إلى تقارب إلكترون أقل سالبية.ومع ذلك،هناك استثناءات. في الهالوجينات،يكون للكلور قيمة تقارب إلكتروني أكثر سالبية من الفلور. لكن لماذا؟الفلور هو أصغر ذرة من الهالوجينات و بالتالي،يمر الإلكترون الوارد بتنافر واضح من الإلكترونات الموجودة بالفعل.و رغم هذا،في أنيون الكلوريد،الإلكترون الجديد يضاف إلى الغلاف الثالث،محتلاًمساحة أكبر. هذا يقلل من تنافر الإلكترون-الكترون،مما يجعلها أكثر جاذبية للحصول على إلكترون. بشكل عام،بالتحرك خلال فترة،يصبح تقارب الإلكترون أكثر سالبية.الهالوجينات لها التقارب الإلكتروني الأكثر سالبية،حيث يساعد الإلكترون الوارد في الوصول إلى تكوين الغاز النبيل. بالمقارنة،فإنّالغازات النبيلة تحتوي على غلاف مملوء بالكامل. يجب استيعاب الإلكترون الوارد في مستوى الطاقة الرئيسي الأعلى،و هذا غير مفضل طاقياًوبالتالي،فإن تقارب الإلكترون لهذه العناصر إيجابي.تظهر استثناءات في المجموعة 2. يشير تكوين الإلكترون إلى أن الإلكترون الوارد يحتاج للدخول لغلاف فرعية ذو طاقة أعلى. وبالتالي،فإن قيم تقارب الإلكترون تكون إما موجبة أو أقل طاردة للحرارة.ومن المثير للاهتمام أن المجموعة 15،لديها تقارب إلكترون أقل سالبية من المجموعة 14. لنقارن بين الفوسفور والسيليكون. على عكس السيليكون،يحتوي الفوسفور على غلاف فرعي نصف ممتلئ،ويحتاج الإلكترون الوارد أن يقترن بإلكترون مقيم بالفعل في المدار p.هذا من شأنه أن يزيد من تنافر الإلكترون-الكترون،وبالتالي فهي عملية غير مفضلة طاقياًوالتي تنعكس أيضًا في التقارب الإلكترونى الأقل سالبية،مقارنة بالسيليكون.

التجاذب الالكتروني

يمثل انجذاب الإلكترونات (EA) تغييراً في الطاقة لإضافة إلكترون إلى ذرة في حالتها الغازية لتكوين أنيون (أيون سالب). <img alt="Eq1" src="https://www.jovecore.com/CDNSource/lessons/1050/1050_Equations-01.png" style="height: 40px;" />يمكن أن تكون هذه العملية إما ماصة للحرارة أو مصدرة للحرارة، وفقاً للعنصر. تحتوي العديد من هذه العناصر على قيم سالبة لـ EA، مما يعني أن الطاقة يتم إطلاقها عندما تقبل الذرة الغازية الإلكترون. ومع ذلك، بالنسبة لبعض العناصر، فإن الطاقة مطلوبة لكي تصبح الذرة مشحونة بشكل سلبي، وقيمة EA إيجابية. وكما هي الحال مع طاقة التأين، فإن قيم EA اللاحقة ترتبط بتكوين الأيونات مع المزيد من الشحن. أما الطاقة الثانية فهي الطاقة المرتبطة بإضافة إلكترون إلى أيون لتكوين أيون 2–، وهكذا. وكما يمكن للمرء أن يتنبأ، يصبح من الأسهل إضافة إلكترون عبر سلسلة من الذرات مع زيادة الشحن النووي الفاعل للذرات. ومع الانتقال من اليسار إلى اليمين عبر مجموعة دوريّة، تميل قيم EA إلى أن تصبح أكثر سلبية. ويمكن فهم الاستثناءات الواردة بين عناصر المجموعة 2 (2A) والمجموعة 15 (5A) والمجموعة 18 (8A) على أساس الهيكل الإلكتروني لهذه المجموعات. والغازات النبيلة، المجموعة 18 (8A)، لها غلاف مملوء تماما، ويجب إضافة الإلكترون القادم إلى مستوى أعلى من n، وهو أمر أكثر صعوبة. تحتوي المجموعة 2 (2A) على هيكل فرعي مملوء من ns، ولذلك ينتقل الإلكترون التالي إلى مستوى الطاقة الأعلى np، لذا، مرة أخرى، لا تكون قيمة EA التي تمت ملاحظتها كما يتوقع الاتجاه. وأخيراً، تحتوي المجموعة 15 (5A) على هيكل فرعي np نصف مملوء، ويجب إقران الإلكترون التالي بإلكترون np موجود. في كل هذه الحالات، يؤدي الاستقرار النسبي الأولي للتكوين الإلكتروني إلى إبطال النزعة في EA. قد يتوقع المرء أن تكون الذرة الموجودة في أعلى كل مجموعة لها EA الأكثر سلبية ؛ وتشير قدرات التأين الأولى إلى أن هذه الذرات لها أكبر شحنات نووية فعالة. ومع ذلك، بينما نتحرك إلى أسفل مجموعة، نرى أن العنصر الثاني في المجموعة غالباً ما يكون له أعلى مستوى سلبي من EA. ويمكن أن يعزى ذلك إلى الحجم الصغير للغلاف n = 2 وما ينتج عن ذلك من عمليات كبيرة لتنافر الإلكترون-الإلكترون. على سبيل المثال، يحتوي الكلور، ذو قيمة EA التي تبلغ –348 كيلوجول/مول، على أعلى قيمة لأي عنصر في الجدول الدوري. تبلغ وحدة EA من الفلورين –322 كيلوجول/مول. عندما نضيف إلكترون إلى ذرة فلور لنكوّن أيون فلوريد (F–)، نضيف إلكترون إلى الغلاف n = 2. ينجذب الإلكترون إلى النواة، ولكن هناك أيضاً تنافر كبير من الإلكترونات الأخرى الموجودة بالفعل في هذه الحاوية الصغيرة للتكافؤ. تحتوي ذرة الكلور على نفس التوزيع الإلكتروني في غلاف التكافؤ، ولكن لأن الإلكترون الداخل يدخل في الغلاف n = 3، فإنها تحتل مساحة أكبر بكثير من الفضاء، كما تقل التنافرات الإلكترونية. إن الإلكترون الداخل لا يحصل له ذات القدر من التنافر، وتقبل ذرة الكلور إلكترونات إضافية بسهولة أكبر، الأمر الذي يؤدي إلى زيادة سلبية في EA. هذا النص مقتبس من <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>

تقارب الإلكترون (EA) هو تغير الطاقة لإضافة إلكترون إلى ذرة غازية لتكوين أنيون (أيون سالب).

يمكن أن تكون هذه العملية إما ...

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Periodic Properties of the Elements

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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 follow the same idea for ions with even more charge.

Across a period, electron affinity usually becomes more negative from left to right. This pattern fits the increase in effective nuclear charge, which makes it easier for atoms to attract an added electron. Some groups do not follow the trend well, though. Group 2 has a filled ns subshell, group 15 has a half-filled np subshell, and group 18 has a full shell, so the next electron must enter a less favorable state.

These exceptions are linked to electron arrangement and stability. Noble gases must place the new electron in a higher n level. Group 2 elements add the electron to a higher-energy np orbital. Group 15 elements must pair the new electron with one already in the np subshell. In each case, the stable starting configuration changes the expected electron affinity.

Down a group, the most negative electron affinity is often found in the second element rather than the top one. The small size of the n = 2 shell can create stronger electron-electron repulsions. That is why chlorine has a more negative electron affinity than fluorine. Chlorine’s value is −348 kJ/mol, while fluorine’s is −322 kJ/mol. When fluorine gains an electron, the added electron enters the small n = 2 shell. In chlorine, the electron goes into the larger n = 3 shell, so repulsion is lower and the atom accepts the electron more readily.

Electron Affinity Trends on the Periodic Table

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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

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ionic radii

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...

electron affinity

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...

alkali metals

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...

halogens

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...

noble gases

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...

key terms and concepts

Learn how electron affinity changes across the periodic table, why some groups are exceptions, and why chlorine has a more negative value than fluorine.

Electron Affinity Trends on the Periodic Table | JoVE K12

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Electron Affinity Trends on the Periodic Table

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