Of all the electrons that form part of an atom, the valence electrons are the only ones that participate when atoms combine to form a bond. In ionic bonding, electrons are transferred (either lost or gained), whereas in covalent bonding, two electrons are shared between the two atoms. Double or triple bonds are formed when atoms share more than one electron pair. The atoms do so to attain the stable octet configuration of 8 electrons in their valence shell.
Learning Objective: To learn about the atomic mass number using protons and neutrons.
Skill Level – Intermediate
Prerequisites:
While nucleophiles donate two electrons in exchange for forming two-electron covalent bonds with the electrophiles, the negative charge due to the two electrons is not obvious in many instances. Neutral molecules like Benzene, water, and ammonia can act as nucleophiles.
A broad way to categorize nucleophiles is as charged or neutral (uncharged).
Metallic solid consists of several metal atoms of the same kind bonded together closely. Due to their large size, metals easily lose their outermost valence electrons. The delocalized valence electron drifts and is now available for the other nuclei of metal atoms. Several delocalized electrons are comparable to a sea of electrons.
As a reactive species, a methylene refers to an electron-deficient carbene, represented as :CH2.
Carbenes are carbon-containing electrophiles that contain only 6 valence electrons instead of the standard eight required for stability. It has an unshared electron pair and two bonds, making it a divalent species, highly unstable, having a fleeting existence. Though classified as electrophiles, methylene species have no formal charge and are neutral.
Learning Objective: To learn about positional isomerism, a subtype of structural isomerism.
Skill Level – Intermediate
Prerequisites:
| Atomic Number | Mass Number |
|---|---|---|
Represents | The total number of protons present in the nucleus of an atom. | Total count of protons and neutrons present in the nucleus of an atom. |
Symbol | Z (AZE) Found at the subscript of the AZE notation while representing the element (E). |
On the dissolution of a substance in a dispersion medium, the aggregation of a vast number of atoms or smaller molecules of varying sizes (< 10-9 m) leads to the formation of colloidal particles of the size range 10-9 to 10-6 m.
As the colloidal particles are now made up of many atoms or molecules, it is now called multimolecular colloids.
The first time the use of two dots or a colon (:) to represent two electrons acting as connecting links between the two atoms was proposed by G.N. Lewis in 1916.
In his landmark paper, ‘the atom and the molecules,’ he attempted to draw molecular structures using dots to represent the covalent nature of the chemical bonds, now popularly known as the Lewis structures.
So, a molecule of Cl2 was Cl : Cl, two electrons connecting two Cl atoms.