chem

Definition: Covalent Bond
- A bond formed between two nonmetal atoms.
- Atoms share electrons in a manner that allows each atom to achieve a stable electron configuration (octet rule).
Covalent Compounds/Molecules
- Groups of atoms held together by covalent bonds.

Molecular Formula
- A type of formula that shows the quantity and types of atoms present in one molecule of a compound.
Lewis Structure
- A diagram that illustrates the connections between atoms within a molecule alongside the position of non-bonding (lone pairs) valence electrons.

Pair electron dots until all atoms achieve their octet.
- Exceptions:
- Hydrogen requires only a duet.
- Boron and aluminum may display a sextet.

Initial Steps:
- Arrange atoms naturally on paper, connect each with single bonds.
- Add lone pairs to fill octets (or doublets for Hydrogen).
Counting Electrons:
- Tally the number of valence electrons used from your sketch.
- Compare with the permissible number from the periodic table.
- For each 2 excess electrons, replace 2 lone pairs with a multiple bond, thus decreasing the total electron count by 2 while maintaining the octet.

Memorization:
- Names and bond angles of molecular shapes from pages 114-119 of the text.
VSEPR Model
- Molecular shapes predict based on the valence-shell electron-pair repulsion approach, as negatively charged electron clouds repel each other and orient far apart.
- Central atom electron clouds are termed electron domains.

Draw the Lewis structure of the molecule.
Count electron charge clouds around the central atom.
- Multiple central atoms should be assessed individually.
Predict the molecular shape based on the orientation of charge clouds maximizing space between them.

Definition:
- Polyatomic ions consist of covalent compounds with an overall charge.
Lewis Structure Drawing
- Use methods previously discussed while considering
- Extra electrons for anions.
- Missing electrons for cations.

Electronegativity Defined:
- A measure of the attraction an atom possesses towards a shared pair of electrons.
Trends in Electronegativity:
- Increases up and to the right across the periodic table, mirroring trends found in ionization energy and electron affinity.
Bond Types:
- In diatomic molecules like H₂ and Cl₂, electrons are shared equally, forming nonpolar bonds with an electronegativity difference (ΔEN) of 0.0-0.4.
- In molecules with different atoms, such as H-Cl:
- Chlorine has a higher attraction leading to polar bonds, where Cl carries a partial negative charge (δ-) and Hydrogen bears a partial positive charge (δ+), characterized by ΔEN of 0.5–1.9.

Molecule Polarity:
- A molecule is polar if it exhibits a δ- (partial negative) and a δ+ (partial positive) side.
- Polar bonds in a molecule denote molecular polarity, unless all polar charges cancel out, resulting in a nonpolar molecule.
Importance: Determining a molecule's polarity is crucial throughout the course.

If either condition fails and at least one polar bond exists, the molecule is classified as polar.

Naming Convention:
- The element with lower ionization energy is listed first.
- The first element is named using the corresponding Greek prefix for the number of atoms (note that “mono” can be optional for the first element).
- The second element is named with an -ide suffix and must include the Greek prefix (with “mono” being mandatory for the second element).

Usually consist of nonmetal-nonmetal pairs.
Physical states at room temperature include solids, liquids, or gases, compared to ionic compounds which are always solids.
Characterized by lower melting and boiling points, unlike ionic compounds that exhibit high melting and boiling points.
Molecular compounds do not conduct electricity, even when dissolved or molten, unlike ionic compounds which conduct when dissolved or melted.

Covalent Bond Summary:
- Formed by sharing electrons, contrasting with complete electron transfer in ionic bonds.
- Two electrons indicate a single bond, four indicate a double bond, six a triple bond.
- Atoms held by covalent bonds form a molecule where lone pair overlap on another vacant orbital results in a coordinate covalent bond.
- Atoms share electrons to reach noble gas configurations.
Key Points:
- Molecular formulas articulate the composition of a molecule; Lewis structures reveal atom connections.
- Bonds visualized as lines denoting covalent connections with lone pairs as dots.
- Shapes determined by the electron pairs using VSEPR model, yielding geometries of linear, planar triangular, or tetrahedral based upon electron charge clouds count.
- Polarity is determined by bond sharing inequality; electronegativity measures an atom's attraction to electrons, peaking on the table's upper right and dipping on the lower left.
- Polar and nonpolar molecules, influenced by bond arrangements and bond cancels, significantly affect physical properties.