Significant Figures
Sig figs are like witnesses at a crime scene. A witness who says "the car was traveling about 60 mph" gives you 1 significant piece of info. A forensic analyst who says "62.47 mph" gives you 4 significant, credible data points. The more sig figs, the more trustworthy and precise your measurement.
The 4 Golden Rules
Every single number you'll ever encounter follows these four rules — no exceptions, no loopholes.
If a decimal point is Present → count from the Pacific (left) side, starting at the first non-zero digit. If Absent → count from the Atlantic (right) side, starting at the first non-zero digit. This NEVER fails!
🔬 Live Sig Fig Counter — Try It!
The Q1 Answer — Worked Out
a. 17.5000 → 6 sig figs (trailing zeros after decimal = significant)
b. 0.0000625 → 3 sig figs (leading zeros never count — the 6, 2, 5 are all that matter)
c. 6.2200 × 10²³ → 5 sig figs (scientific notation: only the coefficient counts — 6.2200)
🏆 Winner: Option (a) with 6 significant figures!
When calculating drug doses, sig figs = patient safety. A nurse calculating "0.50 mg" vs "0.5 mg" communicates different precision. The difference between 1.0 mL and 1 mL in a syringe can matter enormously with high-alert medications like heparin or insulin. Precision in measurement is literally life-saving.
Density & Mass/Volume
Prof. Tehrani already nailed this one — density is like how packed a concert crowd is. An empty arena has low density. Mosh pit at a Metallica show? Maximum density. Same space, different "packing." In chemistry: same volume, different mass = different density.
The Magic Triangle — Never Forget Which Formula to Use
Cover the variable you WANT to find:
🔺 Cover D → you get M ÷ V
🔺 Cover M → you get D × V
🔺 Cover V → you get M ÷ D
Q2 Worked Solution — Step by Step
- Identify what you know
Density = 0.70 g/mL, Mass = 80 g, Volume = ? (unknown)
- Rearrange the formula
D = M/V → V = M/D → V = 80g ÷ 0.70 g/mL
- Calculate
V = 114.3 mL ← note the sig figs: 2 sig figs in 0.70, but we report 3 here for clarity
🧪 Interactive Density Calculator
IV fluid preparation uses this exact formula. Normal saline is ~1.005 g/mL. Knowing density lets pharmacists and nurses calculate how many grams of NaCl are in a given volume bag — critical for patients with hypo/hypernatremia. Blood has a density of ~1.06 g/mL, which is how a centrifuge separates plasma from red blood cells!
Classifying Molecules
Think of molecules like families at a dinner table. Diatomic = couple (2 people). Triatomic = family of 3. Homoatomic = identical twins (same kind). Heteroatomic = mixed family (different people from different backgrounds). CO₂ is like a mom with two identical kids — 3 total family members, but two different "types" of people.
By Atom Count
Monatomic: 1 atom — He, Ne, Ar (noble gases)
Diatomic: 2 atoms — H₂, O₂, N₂, Cl₂
Triatomic: 3 atoms — H₂O, CO₂, SO₂
Polyatomic: 4+ atoms — CH₄, C₆H₁₂O₆
By Atom Type
Homoatomic: Only ONE element — O₂, N₂, P₄
Heteroatomic: TWO or more elements — H₂O, CO₂, NaCl
These two classification systems are independent — a molecule can be both diatomic AND homoatomic (like O₂), or triatomic AND heteroatomic (like CO₂).
Mono=1, Di=2, Tri=3, Tetra=4, Penta=5... These same Greek prefixes appear EVERYWHERE — covalent naming, surgical prefixes (trimeter?), drug names. Learn them once, use them forever. Trigeminal neuralgia? Tri = 3 branches of the nerve!
CO₂ Breakdown
CO₂ = 1 Carbon + 2 Oxygen = 3 atoms total → Triatomic ✓
CO₂ has C AND O = two different elements → Heteroatomic ✓
So CO₂ earns BOTH labels simultaneously — just like a person can be both "tall" and "brunette"!
Mass vs. Weight
Here's the most mind-bending distinction in basic science: Mass never changes. Weight does. If you weigh 70 kg on Earth, you'd weigh about 11.5 kg on the Moon — but your mass is still exactly 70 kg everywhere in the universe. Mass is how much matter you ARE. Weight is how hard gravity pulls on that matter.
Mass
Definition: The amount of matter in an object
Unit: grams (g), kilograms (kg)
Changes with gravity? ❌ Never
Measured by: Balance/scale
Weight
Definition: The force of gravity on an object
Unit: Newtons (N), pounds (lbs)
Changes with gravity? ✅ Yes!
Formula: W = m × g
In pharmacology and nursing, we ALWAYS use mass (kg or g), never "weight" in the colloquial sense. Drug dosing is in mg/kg — the patient's mass in kilograms. This is why scales in hospitals read out in kg. Dosing error prevention starts with understanding this distinction.
Temperature Conversions
Fahrenheit = the American way (water freezes at 32°F, boils at 212°F). Celsius = the scientific/world way (water: 0°C to 100°C). Kelvin = the universe's way — starts at absolute zero, the coldest anything can ever be (-273°C). There's no such thing as negative Kelvin. It's the only scale with a true zero.
The Conversion Formulas
Q5 Worked — 88°F to Kelvin
- Start with the combined formula
K = (5/9)(°F − 32) + 273
- Plug in 88°F
K = (5/9)(88 − 32) + 273 = (0.556)(56) + 273
- Calculate
= 31.11 + 273 = 304.11 K ≈ 304 K
🌡️ Live Temperature Converter
Normal body temperature is 37°C = 98.6°F = 310 K. A fever of 40°C (104°F) = 313 K. Kelvin matters in lab contexts: gas law calculations for respiratory therapy, anesthesia machines, and hyperbaric oxygen chambers all use Kelvin — PV = nRT requires absolute temperature!
Atomic Structure
An atom is like a tiny solar system. The nucleus (protons + neutrons) is the Sun — heavy, dense, at the center. The electrons are the planets — zipping around in orbits (shells), incredibly light, covering huge distances relative to the nucleus. If the nucleus were the size of a marble, the atom itself would be the size of a football stadium!
The Three Key Relationships
🔵 Atomic Number (Z) = # of protons = defines what element it is — change this and you change the element entirely!
🟡 Atomic Mass Number (A) = # of protons + # of neutrons
⚡ # Electrons = # Protons (in a neutral atom, always!)
🔶 # Neutrons = A − Z (mass number minus atomic number)
⚛️ Atom Explorer — Select Any Element
Oxygen is always atomic number 8 (8th on periodic table). Mass number is 16. So neutrons = 16 − 8 = 8. Neutral atom so electrons = protons = 8. Everything about oxygen at its most common isotope = 8, 8, 8. The "lucky number" isotope!
Isotopes are atoms of the same element with different neutron counts. ¹³¹I (iodine-131) is a radioactive isotope used to treat thyroid cancer — same protons as normal ¹²⁷I, but 4 extra neutrons make it unstable and radioactive. The thyroid gland absorbs ALL iodine indiscriminately, delivering targeted radiation. This is nuclear medicine in action!
Periodic Table Navigation
The periodic table is literally a grid map. Groups (columns) are like avenues running north-south — families of similar elements. Periods (rows) are like streets running east-west — elements in the same electron shell level. Finding an element? "Take Street 3, Avenue 2" = Magnesium. It's Manhattan for molecules!
Orientation Rules
🔛 Period = horizontal row (left → right)
↕️ Group = vertical column (up ↕ down)
There are 7 periods and 18 groups
Period 1 = H and He (only 2 elements — 1 shell). Period 2 = Li to Ne (8 elements — 2nd shell fills up). Etc.
Finding Period 3, Group 2
Period 3 = row 3 (Na, Mg, Al, Si, P, S, Cl, Ar)
Group 2 = column 2 (Be, Mg, Ca, Sr, Ba, Ra)
Intersection = Magnesium (Mg) ✓
Group 2 = alkaline earth metals. All form 2+ cations. All have 2 valence electrons!
"Periods go across like pages" — you read across a page (left to right) = periods go horizontal. "Groups go up like Grapes on a vine" — grapes grow on vertical vines = groups are vertical. Period → horizontal. Group → vertical.
Valence Electrons & Groups
Think of an atom as an apartment building. Each floor (shell/energy level) has a limited number of rooms. Valence electrons are the tenants on the top floor — they're the ones who interact with neighbors (other atoms), sign leases (form bonds), and drive all of chemistry. Electrons on lower floors? They're safely tucked away and chemically inert in most reactions.
The Shortcut: Group Number = Valence Electrons
For the main group elements (Groups 1, 2, 13–18), the group number tells you the valence electron count directly:
Group 1 → 1 valence e⁻ (Li, Na, K...)
Group 2 → 2 valence e⁻ (Be, Mg, Ca...)
Group 13 → 3 valence e⁻ (B, Al...)
Group 17 → 7 valence e⁻ (F, Cl, Br...)
Group 18 → 8 valence e⁻ (Noble gases — full outer shell!)
Calcium (Group 2) readily loses its 2 valence electrons to form Ca²⁺. This ion is fundamental in physiology: cardiac action potentials, muscle contraction (including the heart!), neurotransmitter release, bone mineralization, and blood clotting. The drug class "calcium channel blockers" (amlodipine, diltiazem) exploits this directly — blocking Ca²⁺ entry into cardiac muscle cells to lower heart rate and BP.
Ions: Cations & Anions
Electrons are like social media followers. Atoms want a full outer shell — that's the "perfect follower count" (8 for most = octet rule). Metals on the left side say "I have too many — I'll donate them" → become cations (+). Nonmetals on the right say "I need more!" → steal electrons → become anions (−). The driving force of ALL ionic chemistry!
Cations (+) — Metals Lose
Formula: Lose electrons → fewer electrons than protons → net positive charge
Examples:
Na → Na⁺ (loses 1e⁻)
Mg → Mg²⁺ (loses 2e⁻) ✓ Q10
Ca → Ca²⁺ (loses 2e⁻)
Al → Al³⁺ (loses 3e⁻)
Anions (−) — Nonmetals Gain
Formula: Gain electrons → more electrons than protons → net negative charge
Examples:
F → F⁻ (gains 1e⁻)
O → O²⁻ (gains 2e⁻)
N → N³⁻ (gains 3e⁻)
S → S²⁻ (gains 2e⁻) ✓ Q9
CAT-ion — a CAT has PAWS (PAWSitive = positive). Cations are positive.
AN-ion — AN-ion has a negative connotation. Anions are negative.
Why S²⁻? Sulfur is in Group 16 → has 6 valence electrons → needs 2 more to fill its outer shell to 8 → gains 2 electrons → charge = −2.
| Element | Group | Ion Formed | Electrons Lost/Gained | Type |
|---|---|---|---|---|
| Na | 1 | Na⁺ | Loses 1 | Cation |
| Mg | 2 | Mg²⁺ | Loses 2 | Cation |
| Al | 13 | Al³⁺ | Loses 3 | Cation |
| N | 15 | N³⁻ | Gains 3 | Anion |
| O | 16 | O²⁻ | Gains 2 | Anion |
| S | 16 | S²⁻ | Gains 2 | Anion |
| Cl | 17 | Cl⁻ | Gains 1 | Anion |
Every single electrolyte on a BMP/CMP panel is an ion: Na⁺, K⁺, Cl⁻, HCO₃⁻, Ca²⁺, Mg²⁺. When a patient has hypokalemia (low K⁺), we're talking about insufficient potassium cations in the blood. IV replacement therapy literally puts ions back into circulation. Understanding ionic charges = understanding electrolyte physiology.
Periodic Trends
Imagine a tug-of-war between the nucleus and the outer electrons. More protons = stronger pull = harder to remove an electron = higher ionization energy + smaller atomic radius. More electron shells = electrons are farther away = weaker pull = easier to remove = lower ionization energy + larger radius. It's ALL about nuclear attraction vs distance!
⚡ Ionization Energy
⚛️ Atomic Size (Radius)
Ionization energy and atomic size move in exactly opposite directions. Big atom = low IE. Small atom = high IE. If you know one trend, you automatically know the other. Think: a small, dense nucleus with lots of protons holds electrons TIGHTLY (hard to remove = high IE, small size). Big fluffy atom with few protons? Electrons hang loose (easy to remove = low IE, large size).
Chemical Nomenclature
Chemical naming is like baby naming with rules. Ionic compounds are like traditional families — the metal parent's name comes first, unchanged (Dad's name). The nonmetal parent gets a nickname ending in "-ide" (Mom becomes "oxide" or "sulfide"). Covalent compounds are like modern naming — we count how many of each child there are with Greek prefixes (one child = no prefix/mono, two = di, four = tetra).
Ionic Naming Rules
Formula: Metal name + Nonmetal stem + "-ide"
NaCl → Sodium + chlor + ide = Sodium Chloride
Na₂S → Sodium + sulf + ide = Sodium Sulfide ✓
CaO → Calcium + ox + ide = Calcium Oxide
The subscript numbers in Na₂S tell you the ratio (charge balance), not the name!
Covalent Naming Rules
Formula: [Prefix]element1 + [Prefix]element2stem + "-ide"
CO = carbon monoxide (1 oxygen)
CO₂ = carbon dioxide (2 oxygens)
CBr₄ = carbon tetrabromide ✓
"mono" is SKIPPED for the FIRST element only — never say "monocarbon"!
🔤 Naming Builder — Ionic Examples
Metal + Nonmetal = Ionic (use "-ide" naming, no prefixes)
Nonmetal + Nonmetal = Covalent (use Greek prefix naming)
Quick check: Is the first element a metal? Look at the left side of the periodic table. Metals = ionic. Both elements on the right? Covalent. Na₂S → Na is a metal → ionic. CBr₄ → C is a nonmetal → covalent!
Pharmaceutical nomenclature borrows directly from chemistry. Sodium chloride (NaCl = ionic, metal + nonmetal) is normal saline. Nitrous oxide (N₂O = covalent, nonmetal + nonmetal) is laughing gas used in anesthesia. Carbon dioxide (CO₂) — the molecule we're constantly monitoring in ABGs. You're already naming clinical compounds correctly!
Interactive Resources
🌐 Best Interactive Websites for CHM-130
These are handpicked resources that complement exactly what's in Week 1. Bookmark them all!
📱 Recommended YouTube Channels
Professor Dave Explains — Short, clear chemistry videos perfect for CHM-130 level
Crash Course Chemistry — Entertaining, fast-paced overviews of every topic
Tyler DeWitt — Best for visual learners; specializes in making chemistry analogies memorable
The Organic Chemistry Tutor — Extensive practice problems with worked solutions; excellent for exam prep