Chemistry 11

Electrons occupy orbitals — regions of space where an electron is likely to be found — grouped into energy levels (shells) and sublevels ($s$, $p$, $d$, $f$), not fixed circular orbits.

Valence Shell Electron Pair Repulsion (VSEPR) theory: electron-pair regions (bonding pairs AND lone pairs) around a central atom repel each other and spread out as far apart as possible, giving the molecule its 3-D shape.

Valence electrons are the electrons in an atom's outermost occupied energy level; for main-group elements, the number of valence electrons matches the group number (e.g. oxygen, group 16/6A, has 6).

Electronegativity is how strongly an atom pulls on shared electrons; it generally increases across a period and decreases down a group on the periodic table.

Each polar bond has a dipole (a direction of electron pull); whether the WHOLE molecule is polar depends on whether those bond dipoles cancel or add up, which is decided by the molecule's VSEPR shape.

Organic compounds are built on carbon chains or rings; the family (alkane — single bonds only, alkene — a C=C double bond, alkyne — a C≡C triple bond, alcohol — an $-\text{OH}$ group, and others) is identified by its functional group.

Organic compounds are the basis of fuels (gasoline, natural gas), materials (plastics, synthetic fibres), and pharmaceuticals — each application relies on the specific properties of a functional-group family.

IUPAC names encode the chain length with a root (meth-, eth-, prop-, but-…) and the family with a suffix (-ane, -ene, -yne, -ol); e.g. $\text{C}_3\text{H}_8$ is propane, $\text{C}_2\text{H}_5\text{OH}$ is ethanol.

Many communities, including First Peoples communities, have long-standing traditional practices using organic materials (medicines, agriculture, food, biotechnology) that connect traditional knowledge with modern organic chemistry.

A mole is a counting number, like a dozen (12) but far larger: $6.022 \times 10^{23}$ particles (Avogadro's number). One mole of any substance contains this many atoms, molecules, or formula units.

A conversion factor is a fraction equal to 1 (e.g. $\frac{1000\ \text{mL}}{1\ \text{L}}$); multiplying by it changes the units without changing the actual amount.

Molar mass (g/mol), found from the periodic table, converts between mass and moles; Avogadro's number converts between moles and number of particles — the mole is the hub connecting both.

Chain conversion factors so each unwanted unit cancels diagonally, leaving only the target unit — this works for single-step or long multi-step conversions alike.

The five common reaction types are synthesis (A + B → AB), decomposition (AB → A + B), single replacement (A + BC → AC + B), double replacement (AB + CD → AD + CB), and combustion (a fuel + $\text{O}_2$ → $\text{CO}_2$ + $\text{H}_2\text{O}$).

An exothermic reaction releases energy to its surroundings (often felt as heat, surroundings warm up); an endothermic reaction absorbs energy from its surroundings (surroundings cool down).

The coefficients of a balanced equation give the mole ratio between any two substances in the reaction.

Any molar quantity — number of molecules (via Avogadro's number), gas volume, or another molar amount — can be found the same way mass is: convert the given quantity to moles, apply the mole ratio, then convert to the quantity you need.

The limiting reactant is the one that runs out first and stops the reaction — it determines the maximum ("theoretical") amount of product that can form, no matter how much of the other (excess) reactant remains.

"Like dissolves like": polar solvents (like water) dissolve polar and ionic solutes well, while nonpolar solvents dissolve nonpolar solutes well, because similar particles can form strong attractions with each other.

Molar concentration, $c = \dfrac{n}{V}$ (mol/L), relates the moles of dissolved solute to the volume of the whole solution.

The dilution effect: adding solvent increases the volume but keeps the moles of solute constant, so the solution becomes less concentrated while the same amount of solute is simply more spread out.

When two ionic solutions are mixed, first dissociate each compound into its ions and find the moles of each ion; each ion's moles are conserved, but they are now spread through the COMBINED total volume of both solutions.

Titration measures an unknown concentration by carefully adding a solution of known concentration until the reaction is exactly complete (the equivalence point), often signalled by an indicator.

Significant figures are all the digits in a measurement known with certainty plus one estimated digit; rules cover which digits count (nonzero digits always count; leading zeros never count; zeros between or trailing after a decimal point count).

Uncertainty describes the range within which a measurement's true value likely falls (e.g. $12.5 \pm 0.1$ mL), reflecting the limits of the instrument used; accuracy is closeness to the true value, precision is closeness of repeated measurements to each other.

When calculating, the final answer is rounded to match the LEAST precise measurement used — multiplication/division rounds to the fewest significant figures among the inputs; addition/subtraction rounds to the fewest decimal places.

Scientific notation ($a \times 10^n$, with $1 \le a < 10$) expresses very large or very small measurements compactly and makes the number of significant figures explicit, e.g. $6.022 \times 10^{23}$.