CHEM 1113 Quiz 1— Balancing, Stoichiometry, Atomic Structure & Bonding

Quiz Overview Format: 3–4 multiple choice questions, 6 minutes total (~90 sec/question) Topics: Balancing reactions, stoichiometry, atomic structure, chemical bonding Style: Quick concept checks, not heavy math What to expect by topic: ⚖️ Balancing reactions — pick the correctly balanced equation 🧮 Stoichiometry — conversion setup (grams↔moles, mole ratios, limiting reagent), clean numbers ⚛️ Atomic structure — find atomic number, mass number, or isotopes from proton/neutron/electron counts 🔗 Bonding — classify ionic vs. covalent vs. polar covalent, predict ion charges Watch out for: Isotope vs. ion mix-ups Atomic number vs. mass number mix-ups

Reactant vs product

Reactants are on the left of the arrow, products are on the right

Law of conservation of mass (states 2 facts)

Mass and the number/type of atoms in reactants equals products, atoms are only rearranged

What can change in a reaction

The physical state of matter and how atoms are grouped together

Balancing an equation

Adjusting coefficients so each atom's count matches on both sides

Complete combustion

Hydrocarbon fuel + O2 reacts to make CO2 + H2O + energy

reaction exothermic

Avogadro's number

6.022x10^23 particles per mole

Mole

Unit containing 6.022x10^23 particles

Molar mass

Mass in grams of one mole of a substance, converts grams to moles

Grams to moles to particles pathway

Divide by molar mass to get moles, multiply by Avogadro's number to get particle count

Stoichiometric (mole) ratio

Ratio between reactants/products set by a balanced equation's coefficients

Limiting reagent

The reactant that runs out first and limits product formed

Excess reagent

The reactant left over after the reaction stops

Proton

Positively charged nucleus particle, mass about 1 amu

Neutron

Neutral (uncharged) nucleus particle, mass about 1 amu

Electron

Negatively charged particle around the nucleus, about 1800x lighter than a proton

Atomic number

Number of protons, defines the element

Mass number

Protons + neutrons, electrons too light to count

Neutral atom rule

Number of protons equals number of electrons

Isotope

Atoms of the same element with different numbers of neutrons

Average atomic mass

Weighted average of an element's isotopes based on % natural abundance

Valence electrons

Outermost-shell electrons, determine how an atom bonds

Core electrons

Inner-shell electrons, not involved in bonding

Atomic orbital shapes and order

s is a sphere, p is a dumbbell, d is four-lobed, energy order is s < p < d < f

Octet rule

Atoms are most stable with 8 valence electrons

Ionic bond

Bond formed by transferring an electron from a metal to a nonmetal
High melting point

Forms latices held together by strong electrostatic force

Coulomb's law

Opposite charges attract, like charges repel

Isoelectronic

Species of atoms with the same number of electrons (e.g. Na+ and Ne)

Ion charges from group number

Group 1 is +1, Group 2 is +2, Group 6 is -2, Group 7 is -1

Why ionic compounds have high melting points

Each ion is surrounded by many opposite-charge ions in a 3D lattice

Covalent bond

Bond formed when two atoms share electrons instead of transferring them

Bonding electrons vs lone pairs

Bonding electrons are shared and hold atoms together, lone pairs stay on one atom

Bond strength order

Triple bond > double bond > single bond

bonds weaken as atoms get bigger

Electronegativity

A measure of an atom's pull on shared electrons when bonded with another atom

Electronegativity trend

Increases left to right and bottom to top

Most electronegative element

Fluorine

How does electronegativity difference determine the type of chemical bond between atoms?

Small difference is nonpolar, medium is polar covalent, large is ionic

Polar covalent bond

Unequal electron sharing, creates partial positive and negative charges