Chemistry: Lewis Theory and Bonding

Atoms gain stability by achieving an electron configuration resembling a noble gas, typically fulfilling an octet (8 electrons) in their outermost shell.

A chemical bond formed through electrostatic attraction between oppositely charged ions (cations and anions).

A chemical bond formed by the sharing of valence electrons between two atoms.

A visual representation of an atom's valence electrons, used to predict how atoms will bond.

A group of atoms held together by covalent bonds, often with a net charge.

A type of covalent bond where two electron pairs are shared between two atoms, represented by a double line.

A type of covalent bond where three electron pairs are shared between two atoms, represented by a triple line.

A molecule formed from two identical atoms, sharing electrons equally.

The formal charge of an atom in a molecule is the difference between the number of valence electrons the atom should have and the number of electrons it actually has in the Lewis structure. It helps predict the most stable arrangement of atoms.

The formula for calculating formal charge is: Formal charge = (# valence electrons) - (# of nonbonding electrons + # of bonds)

When several Lewis structures are possible for a molecule, the structures with the smallest formal charges are considered the most stable and are the preferred representations.

Elements in the third period (and beyond) can expand their valence shell by accommodating more than eight electrons. This allows them to form more than four bonds. This is an exception to the octet rule.

Some elements like boron (B) often have fewer than eight electrons in their valence shell, defying the octet rule.

Resonance occurs when two or more Lewis structures can be drawn for a molecule, each structure contributing to the actual structure. These structures are called resonance forms.

In resonance structures, the more important forms are those that have the smallest formal charges. This contributes to greater stability, making it more likely to be the true structure.

The number of valence electrons for an element is determined by the number of electrons in its outermost shell. The outermost shell is the highest energy level that contains electrons. In CH2O, the outermost shell of Carbon contains 4 electrons, the outermost shell of Hydrogen contains 1 electron and the outermost shell of Oxygen contains 6 electrons. To calculate the valence electrons for CH2O, we add up the number of electrons in the outermost shell of each atom: 4 + 2(1) + 6 = 12 valence electrons

In Step 2 of the process of drawing an electron-dot structure, we arrange the atoms in the molecule. We start by placing the least electronegative atom in the center. In the case of CH2O, Carbon is the least electronegative atom we place it in the center surrounded by the Hydrogen atoms on one side and the Oxygen atom on the other side. So we end up with H-C-H-O.

The electron-dot structure, also known as the Lewis Structure, is a diagram that shows the bonding between atoms of a molecule and the lone pairs of electrons that may exist in the molecule. In Step 3, we place dots around the atoms to represent the valence electrons. The first four electrons are placed in the first shell (s-orbital), and the next four electrons are placed in the next shell (p-orbital). In CH2O, the carbon atom already has four bonds to the hydrogens and the oxygen, so the oxygen atom holds the remaining valence electrons. So, the O has 2 lone pairs of electrons.

In Step 4, we complete the octet rule, which states that atoms tend to gain, lose, or share electrons to have eight electrons in their outer shell for stability. In the case of CH2O, both the Oxygen and the Carbon have completed 8 valence electrons.

The electron-dot structure, also known as the Lewis Structure, is a diagram that shows the bonding between atoms of a molecule and the lone pairs of electrons that may exist in the molecule. In Step 3, we place dots around the atoms to represent the valence electrons. The first four electrons are placed in the first shell (s-orbital), and the next four electrons are placed in the next shell (p-orbital). In ICl3, the Iodine atom already has three bonds to the chlorine atoms, so the chlorine atoms hold the remaining valence electrons. So, each Cl has 3 lone pairs of electrons.

The best resonance structure is the one that has the least amount of formal charge.