chemistry exam 2 week 6 study guide

lecture 8,9,10 and activity 8,9,10

State all of the polyatomic ions you need to know by name, formula, and charge.

Ammonium: NH₄⁺

Hydronium: H₃O⁺

Hydroxide: OH⁻

Cyanide: CN⁻

Nitrate: NO₃⁻

Nitrite: NO₂⁻

Acetate: CH₃COO⁻ (C₂H₃O₂⁻)

Bicarbonate (hydrogen carbonate): HCO₃⁻

Hydrogen sulfate (bisulfate): HSO₄⁻

Carbonate: CO₃²⁻

Sulfate: SO₄²⁻

Sulfite: SO₃²⁻

Phosphate: PO₄³⁻

Peroxide: O₂²⁻

Azide: N₃⁻

Hydrogen sulfite: HSO3⁻

What are the rules for naming with polyatomic ions?

1. Name the cation first, then the anion; polyatomic ions keep their names (e.g., sulfate, nitrate).

2. A monatomic anion takes the -ide ending (e.g., chloride, oxide).

3. Metals with more than one possible charge (most transition metals) get a Roman numeral for their charge, e.g., copper(II) nitrate.

4. Write the formula so total positive and negative charges cancel (net charge = 0).

5. Use parentheses when more than one polyatomic ion is needed, e.g., Ca(NO₃)₂; never change the subscripts inside the ion

What are the rules for naming covalent/ molecular compounds?

1. Used for compounds of two nonmetals; no charges to balance and no Roman numerals.

2. Name the first element with its full element name; add a prefix only if there is more than one atom (never "mono-" on the first element).

3. Name the second element with a prefix + root + -ide (e.g., dichloride, trioxide).

4. Drop the final "a" or "o" of the prefix before a vowel (e.g., monoxide, pentoxide, tetroxide).

What are the pre-fixes needed to name them?

mono- = 1, di- = 2, tri- = 3, tetra- = 4, penta- = 5 hexa- = 6, hepta- = 7, octa- = 8, nona- = 9, deca- = 10

what is VSEPR?

Valence Shell Electron Pair Repulsion theory: electron groups around a central atom repel each other and spread out as far apart as possible. This arrangement predicts the electron geometry and the molecular shape.

Define electron groups (electron densities)

Electron groups are regions of electron density around the central atom. Each lone pair counts as one group, and each bond counts as one group, whether it is a single, double, or triple bond.

Which element harbors an incomplete octet and can only hold up to six e- (3 bonds)? Which element (discussed in lecture) harbors an expanded octet and holds up to 10 e- (5 bonds)

Boron (B) has an incomplete octet: 6 e⁻, 3 bonds (e.g., BH₃, BF₃).

Phosphorus (P) has an expanded octet: 10 e⁻, 5 bonds (e.g., PCl₅, PF₅).