CHEM11 Midterm 2 Study Guide

CHEM11 Midterm 2 F2026 w/ Prof. Gipson

Empirical Formulas

Chemical formulas that show the lowest relative number of atoms of each element in a compound

Molecular Formulas

Formulas that show the actual number of atoms of each element in a molecule

Ionic Bonds

A cation (nonmetal) is attracted to an anion (metal) because the anion wants to lose their electrons while the cation wants to accept the electron

Electron transfer leads to strong lattices

Covalent Bonds

Two nonmetals share electrons between two bonded atoms

Electron sharing leads to molecules

NAMING IONIC COMPOUNDS: MONOATOMIC ANIONS (4.2)
Fluorine

Symbol for Ion: F- (superscript)
Anion Name: Fluroide

NAMING IONIC COMPOUNDS: MONOATOMIC ANIONS (4.2)

Chlorine

Symbol for Ion: Cl- (superscript)

Anion Name: Chloride

NAMING IONIC COMPOUNDS: MONOATOMIC ANIONS (4.2)

Bromine

Symbol for Ion: Br- (superscript) Anion Name: Bromide

NAMING IONIC COMPOUNDS: MONOATOMIC ANIONS (4.2)

Iodine

Symbol for Ion: I- (superscript)
Anion Name: Iodide

NAMING IONIC COMPOUNDS: MONOATOMIC ANIONS (4.2)
Oxygen

Symbol for Ion: O2-
Anion Name: Oxide

NAMING IONIC COMPOUNDS: MONOATOMIC ANIONS (4.2)
Sulfur

Symbol for Ion: S2-

Anion Name: Sulfide

NAMING IONIC COMPOUNDS: POLYATOMIC IONS (4.4)
Acetate

C2H3O2-

NAMING IONIC COMPOUNDS: POLYATOMIC IONS (4.4)
Carbonate

CO32-

NAMING IONIC COMPOUNDS: POLYATOMIC IONS (4.4)

Bicarbonate/Hydrogen Carbonate

HCO3-

NAMING IONIC COMPOUNDS: POLYATOMIC IONS (4.4)

Hydroxide

OH-

NAMING IONIC COMPOUNDS: POLYATOMIC IONS (4.4)

Nitrite

NO2-

NAMING IONIC COMPOUNDS: POLYATOMIC IONS (4.4)

Nitrate

NO3-

NAMING IONIC COMPOUNDS: POLYATOMIC IONS (4.4)

Phosphate

PO43-

NAMING IONIC COMPOUNDS: POLYATOMIC IONS (4.4)

Ammonium

NH4+

NAMING IONIC COMPOUNDS: POLYATOMIC IONS (4.4)
Perchlorate

ClO4-

NAMING IONIC COMPOUNDS: POLYATOMIC IONS (4.4)

Permanganate

MnO4-

NAMING IONIC COMPOUNDS: POLYATOMIC IONS (4.4)

Sulfate

SO42-

NAMING IONIC COMPOUNDS: POLYATOMIC IONS (4.4)

Cyanide

CN-

NAMING IONIC COMPOUNDS: POLYATOMIC IONS (4.4)

Peroxide

O22-

Do polyatomic ions break apart in CHEM 11?

NO!

CALCULATIONS WITH COMPOUNDS
Conversions for grams → moles

Use the molar mass

CALCULATIONS WITH COMPOUNDS

Conversion for moles → formula units

Use Avogadro’s number

FINDING EMPIRICAL FORMULAS

Mass % elements (percent composition) → grams of each element

Assume a 100g sample of entire compound, then use the ratios of each element within the compound

FINDING EMPIRICAL FORMULAS

Grams of each element → moles of each element

Use the molar mass (g/mol)

FINDING EMPIRICAL FORMULAS

Moles of each element → empirical formula

Calculate mole ratio

ELECTRONEGATVITIY AND BOND POLARITY

Pure Covalent Bond/Non Polar Covalent Bond

ΔEN < 0.4, even electron sharing & even pulls

ELECTRONEGATIVITY AND BOND POLARITY

Polar Covalent Bond

ΔEN > 0.4, uneven electron sharing & uneven pulls

RESONANCE AND FORMAL CHARGE

What is formal charge + finding formal charge

Formal charge is the charge an atom were to have if all of the electrons in a covalent bond were shared equally

Formal charge = amount of valence e- in that SPECIFIC atom - (bonding groups + total lone pair electrons)

EXCEPTIONS TO THE OCTET RULE

Incomplete Octets; central atoms having less than an octet

Molecules containing either Boron (B) or Beryllium (Be) as the central atom can make stable compounds with an incomplete octet

EXCEPTIONS TO THE OCTET RULE

Expanded Octets; central atoms with more than eight valence e-

Can only occur with nonmetals from Period 3 or higher because they have d-orbitals available

EXCEPTIONS TO THE OCTET RULE

Free Radicals; central atoms with an unpaired electron

Usually unstable and reactive, but there are atoms in molecules and ions that have an odd number of valence e- (i.e. Nitrogen and Oxygen, where nitrogen has one unpaired valence e-)

BOND ENERGIES AND LENGTHS

As the number of bonds between two atoms increases, the bond length…

The bond length decreases

(think of it like if your bond with somebody increases, you want to be closer with them)

BOND ENERGIES AND LENGTHS

As the number bonds between two atoms increases, the bond energy…

The bond energy increases
(think of it like stronger your bond with somebody, the more you bond with that person)

VSEPR THEORY

Electron Geometry & Bond Angles for 2 Electron Groups

Electron Geometry: Linear

Bond Angles: 180

VSEPR THEORY

Electron Geometry & Bond Angles for 3 Electron Groups

Electron Geometry: Trigonal Planar

Bond Angles: 120

VSEPR THEORY

Electron Geometry & Bond Angles for 4 Electron Groups

Electron Geometry: Tetrahedral

Bond Angles: 109.5

VSEPR THEORY

Molecular Geometry & Bond Angles for 3 Electron Groups, if one of those electron groups is a lone pair

Molecular Geometry: Bent

Bond Angles: <120

VSEPR THEORY

Molecular Geometry & Bond Angles for 4 Electron Groups, if one of those electron groups is a lone pair

Molecular Geometry: Trigonal Pyramidal

Bond Angles: <109.5

VSEPR THEORY

Molecular Geometry & Bond Angles for 4 Electron Groups, if two of those electron groups are lone pairs

Molecular Geometry: Bent
Bond Angles: <109.5

NET DIPOLE MOMENTS & MOLECULAR POLARITY

When do dipoles cancel each other out to create no net dipole moment?

When two dipoles have the same strength but point in opposite directions, that is when there is no net dipole moment.

VALENCE BOND THEORY

Central Themes of Valence Bond Theory

1) Opposing spins of the electron pair
2) The greater the orbital overlap, the closer the nuclei are to the electrons, and the stronger the bond
3) During bonding, the valence orbitals in the isolated atoms become the new orbitals in the molecule

VALENCE BOND THEORY

Hybridization Types

sp - linear electron geometry

sp2 - trigonal planar electron geometry

sp3 - tetrahedral electron geometry

VALENCE BOND THEORY

The # of electron groups is the same as….

The number of superscripts in hybrid name - 1

Stoichiometry

the study of mass relationships in chemistry

TYPES OF COMPOUNDS THAT UNDERGO GAS-EVOLUTION REACTIONS

Reactant Type: Sulfides (S2-)

Intermediate Product: None

Gas Evolved: H2S

TYPES OF COMPOUNDS THAT UNDERGO GAS-EVOLUTION REACTIONS

Reactant Type: Carbonates and Bicarbonates (CO32- or HCO3-)

Immediate Products: a salt, carbon dioxide, and water (H2CO2)

Gas Evolved: CO2

OXIDATION-REDUCTION REACTIONS

LEO goes GER for Reddox Reactions

LEO - lose electrons = oxidation

GER - gain electrons = reduction