Atomic Structure: Electron Configurations

The lowest-energy arrangement, or ground-state electron configuration, of an atom is a listing of the orbitals occupied by its electrons. We can predict this arrangement by following three rules.

Rule 1

The lowest-energy orbitals fill up first, according to the order 1s→2s → 2p → 3s → 3p → 4s → 3d, a statement called the Aufbau principle. Note that the 4s orbital lies between the 3p and 3d orbitals.

Rule 2

   Electrons act in some ways as if they were spinning around an axis, somewhat like how the earth spins. This spin can have two orientations, denoted as up (↑) and down (↓). Only two electrons can occupy an orbital, and they must be of opposite spin, a statement called the Pauli exclusion principle.

Rule 3

If two or more empty orbitals of equal energy are available, one electron occupies each with spins parallel until all orbitals are half-full, a statement called Hund’s rule.

Some examples of how these rules apply are shown in Table 1-1. Hydrogen, for instance, has only one electron, which must occupy the lowest-energy orbital. Thus, hydrogen has a 1s ground-state configuration. Carbon has six electrons and the ground-state configuration 1s2 2s2 2px 1 2py 1, and so forth. Note that a superscript is used to represent the number of electrons in a particular orbital.

Problem 1 - 1

Give the ground-state electron configuration for each of the following elements:

(a) Oxygen (b) Nitrogen (c) Sulfur

Problem 1 - 2

How many electrons does each of the following elements have in its outermost electron shell?

(a) Magnesium (b) Cobalt (c) Selenium

مواضيع ذات صلة

طرق تحضير الحموض الكربوكسيلية

الخواص الفيزيائية للحموض الكربوكسيلية

التسمية النظامية للحموض الكربوكسيلية

الأكسدة والاختزال

التعرف على الألدهيدات والكيتونات

تفاعل كانيزارو

هلجنة الألدهيدات والكيتونات

إضافة مايكل Micheal Addition

تكاثف بيركن Perkin condensation

تفاعلات التكاثف

تفاعلات الإضافة النيكلوفيلية للألدهيدات والكيتونات مع مركبات النيتروجين القاعدية

تفاعلات الإضافة النيكلوفيلية للألدهيدات والكيتونات تكوين أسيتال وكيتال