Drawing Lewis Structures and Predicting Bond Types

Vocabulary flashcards covering Lewis structure rules, step-by-step drawing guidelines, octet rule exceptions, electronegativity calculations, and bond polarity classifications.

Octet Rule Exception for Hydrogen

Hydrogen requires just $2$ electrons to form a noble gas arrangement.

Octet Rule Exception for Boron (B)

Boron (B) requires just $6$ electrons and therefore only makes three bonds.

Octet Rule Exception for Beryllium (Be)

Beryllium (Be) requires just $4$ electrons and therefore only makes two bonds.

Double Bond

Occurs when atoms share two pairs of electrons, forming when there are not enough electrons to complete octets; considered to be two single bonds.

Triple Bond

Occurs when atoms share three pairs of electrons, forming when there are not enough electrons to complete octets; considered to be three single bonds.

Maximum Number of Bonds Formula

In CHEM:1070, calculated as $8 - \text{Group Number} = \text{Maximum number of bonds for an element}$.

Nonpolar Covalent Bond

A chemical bond occurring between nonmetals that has an equal or almost equal sharing of electrons and an electronegativity difference of $\Delta\text{EN} = 0\text{ to }0.4$.

Polar Covalent Bond

A chemical bond typically occurring between nonmetal atoms with an unequal sharing of electrons and a moderate electronegativity difference of $\Delta\text{EN} = 0.5\text{ to }1.8$.

Ionic Bond (Electronegativity Difference)

A bond formed when the electronegativity difference $\Delta\text{EN}$ is greater than $1.8$ ($1.9\text{ and greater}$), where electrons are considered transferred rather than shared.

Dipole

The separation of charges in a polar bond, which becomes more polar as the difference in electronegativity increases.

Electronegativity Difference Formula

Formula used to predict the type of chemical bond: $\Delta\text{EN} = |\text{EN}_2 - \text{EN}_1|$.

Lowercase Greek Letter Delta Notation

The symbol $\delta$ with a positive or negative charge ($\delta^+$ or $\delta^-$) used to indicate the positive and negative ends of a dipole.

Dipole Arrow Direction

An arrow that points from the positive end to the negative end of a dipole.

Step 1 in Guide to Lewis Structures

Count valence electrons.

Step 2 in Guide to Lewis Structures

Draw the skeleton structure.

Step 3 in Guide to Lewis Structures

Add lone pairs to outer atoms to form octets (or duet for H).

Step 4 in Guide to Lewis Structures

Add lone pairs to the inner atom.

Step 5 in Guide to Lewis Structures

Check if the octet is full; if not, make multiple bonds to attain an octet ($8e^-$) on each atom.

Valence Electrons in Methane (CH4)

Totaled as $1\text{C} + 4\text{H} = (1 \times 4e^-) + (4 \times 1e^-) = 8e^-$.

Valence Electrons in CHCl3

Totaled as $4 + 1 + 3 \times 7 = 26$ valence electrons.

Valence Electrons in N2

Totaled as $2\text{ N atoms} \times 5e^- = 10e^-$ total valence electrons.

Electronegativity Difference of N-N Bond

Calculated as $|3.0 - 3.0| = 0.0$, classifying it as a nonpolar covalent bond.

Electronegativity Difference of C-H Bond

Calculated as $|2.5 - 2.1| = 0.4$, classifying it as a nonpolar covalent bond.

Electronegativity Difference of C-Cl Bond

Calculated as $|2.5 - 3.0| = 0.5$, classifying it as a polar covalent bond.

Electronegativity Difference of C-O Bond

Calculated as $|2.5 - 3.5| = 1.0$, classifying it as a polar covalent bond.