Most Things Biology

2.1 Atoms, Ions, Electrolytes

Case home  ·  Start at the beginning  ·  The Reveal

Time To Read

27–40 minutes

Date Last Modified

Just Enough Chemistry · Chapter 1 of 7

1984, age nine: the worst emergency room yet. A Saturday, a belly so bad she couldn’t straighten her legs, and vomiting — “I threw up on the nurse’s shoes and I’m sorry about that.” Then “the X-ray and the blood,” a doctor pushing on her stomach, a long talk with Mom in the hall with the door not all the way shut, and one word she had to look up in the big dictionary in the den. The chart wrote: “Recurrent abdominal pain, no organic cause. Psychiatry referral.” This chapter starts where blood is just chemistry — elements, atoms, the electrons that make ions, the salts that conduct — so you can read what that blood test counted, and what it never could.

The question you will answer

“Bloodwork shows nothing” sounds like a verdict. Before you can weigh it you need to know what an emergency-room blood panel in 1984 actually counted — a handful of elements in their charged forms, a sugar, a waste product, some cells — and what kind of particle an inflamed belly would have put into the blood instead. The question for the chapter: when a test comes back normal, what exactly has it ruled out?

Opener · The Blood Showed Nothing · about 2¼ minutes

The opener is the same narrated animation you will watch in Scene 1.

Watch it in Scene 1 ↓

Watch the opener first. It sets the question; the chapter answers it.

1

Read the chart

Patient chart · Stina

1984 · age 9 · the worst ER, and what the blood showed

1977–83 · 2–8
Module 1’s years: fevers that come and go, spots that itch then burn, two days of vomiting after a sunburn, “the hot stomach,” legs that hurt at night. At eight, Dr. Gonzalez asks for a calendar with the fever days marked.

1984 · 9
ER on a Saturday for her stomach — “the worst one”: she can’t straighten her legs and throws up on the nurse’s shoes. “They did the X-ray and the blood and pushed on me.” X-ray and bloodwork show nothing. The doctor talks to Mom in the hall; she hears the word psychiatrist. Referred to a psychiatrist.

1984 · 9 · after
Looks up “psychiatrist” in the big dictionary in the den and decides she has Mom’s brain tumor. The psychiatrist: “a nice man with a beard and a fish tank”; they talk about school and Jenny P. and bad dreams. “He never looked at my stomach.” A lollipop; no need to come back. “I still have the stomach.”

Told
“Recurrent abdominal pain, no organic cause. Psychiatry referral.” “A bright, sensitive girl.”

Chart clues this module: 2 · this module (logged in Chapter 7) — undated, “across these years”; no lab values exist for 1984

Before you go on · your prediction

Nine years old, the worst ER visit yet: legs she couldn’t straighten, vomiting, “the X-ray and the blood” — and the blood showed nothing. Before you learn what an ER blood panel counts, what does “showed nothing” most likely mean?

Open the one you lean toward. Nothing is recorded and nothing is revealed — you come back to it at the end.

Nothing was wrong — “Recurrent abdominal pain, no organic cause”

Watch which particles a 1984 panel actually counted, and whether any of them is something an inflamed tissue makes.

She was upset and it settled in her stomach — “a bright, sensitive girl”

Watch whether worry can move a sodium or a potassium number, and whether an ion panel can report on mood at all.

The numbers that were measured came back in range, and they measured something other than inflammation

Watch what a body does to hold its ions steady after one bout of vomiting, and what kind of molecule an attack would actually send into the blood.

From Stina’s diary

Age 9 · “Brain doctor”

2

The story

Three short movements: the case, the anatomy and physiology, then the tie back to Stina. Each links to the scene where you’ll see it move.

I · The worst one

It was a Saturday, and it was the worst one. Stina was nine, and she had been to the emergency room for her stomach before, but this time she couldn’t straighten her legs. She lay curled on the cart with her knees pulled up and threw up on the nurse’s shoes — “and I’m sorry about that,” she wrote, because she was the kind of nine-year-old who apologized in her own diary. They did the X-ray and the blood and pushed on her. Then the doctor took Mom into the hall and talked for a long time with the door not all the way shut, and through the gap Stina heard a word she didn’t know: psychiatrist. At home she found it in the big dictionary in the den — a physician who treats diseases of the mind — and read it three times. By Thursday she had worked it out, and wished she hadn’t. Mom had had a tumor in her brain and they’d had to cut it out, and now they were sending Stina to a brain doctor, so she must have the same thing, and nobody wanted to say it. She decided to be brave and not to ask, because then they would have to say it. The brain doctor turned out to be a nice man with a beard and a fish tank. They talked for a long time about school and Jenny P. and whether she had bad dreams. He never looked at her stomach. He never said anything about a tumor. He gave her a lollipop and told Mom she was “a bright, sensitive girl,” and she didn’t have to go back. “I still don’t know what that was for,” she wrote. “I still have the stomach.”

See it move: Scene 1 · The Blood Showed Nothing · Scene 6 · On the Nurse’s Shoes

II · Elements, ions, and a panel that counts them

Chemistry is the mud everyone braces to slog through. Hold that dread loosely: this is where blood stops being red and starts being countable. Matter is anything that has mass and takes up space; an element is one identity matter can take, and the periodic table is less a chart to memorize than a seating chart of everything there is. Four elements — oxygen (about 65% of your mass), carbon (18), hydrogen (10) and nitrogen (3) — make about 96% of you; most of the rest is calcium, phosphorus, potassium, sulfur, sodium, chlorine and magnesium. Symbols are little fossils of old Latin: Na from natrium, K from kalium — and watch that kal-, because it loves to get confused with calci- for calcium. An atom is the smallest unit of an element that still behaves like that element: positive protons and uncharged neutrons packed in the nucleus, negative electrons out in a cloud. The atomic number counts the protons and is the element’s fingerprint; the mass number adds the neutrons; atoms of one element with different neutron counts are isotopes, and the unstable ones are the radioisotopes a PET scan follows. Now my peanut M&M: the peanut is the nucleus, the first dip of chocolate holds 2 electrons, the next two dips hold 8 each. Full shells win. Sodium (2-8-1) gives away its one lonely outer electron and becomes the cation Na⁺; chlorine (2-8-7) takes it and becomes the anion chloride, Cl⁻ — no hand-holding, no matchmaker required. Dissolve a salt and it dissociates into ions that carry a current: an electrolyte. That is what an ER panel counts, in textbook reference ranges — Na⁺ 135–145 mEq/L, K⁺ 3.5–5.0, Cl⁻ 98–106, HCO₃⁻ 22–28 — beside glucose and urea.

See it move: Scene 2 · The Building Block · Scene 3 · Full Shells Win · Scene 4 · Give One, Take One · Scene 5 · Salts That Conduct

III · A true answer to a narrow question

Here is what you can read into that Saturday that nobody in the room could. “X-ray and bloodwork show nothing” was very likely true. A 1984 emergency room drew blood and asked a few standard questions of it: the electrolytes, the sugar, the urea that tracks the kidneys, a count of red and white cells. The chemistry lines describe balance — whether a body has kept its water and salt, its fuel and its waste where they belong — and a nine-year-old who has vomited usually keeps them where they belong, because her kidneys and the fluid between her cells are built to hold them there. None of them is a line for inflammation; only the white count can lean that way, and it cannot say where or why. The disease you are learning, familial Mediterranean fever, is inflammation with no germ in it: in an attack, white cells in the lining of the belly sound an alarm, and the alarm’s messenger and the emergency proteins the liver makes in reply are proteins — particles an ion panel was never built to count. So the honest sentence was not “nothing is wrong” but “her ions are normal.” The question that mattered — is something inflamed? — had not been asked at all, and the chart turned an unasked question into “no organic cause.” Honesty flag: canon keeps no values from that Saturday, so we do not know exactly which tests were run; this is a reading of what such a panel can and cannot see. Two names to hold for later. The potassium that will leak out of a white cell in Module 3 trips a different alarm sensor, NLRP3 — not pyrin. And the first bags of IV fluid in her diary are hung when she is thirty-one.

See it move: Scene 1 · The Blood Showed Nothing · Scene 6 · On the Nurse’s Shoes

3

Watch · explore · think · check

6 scenes. Each one has a short animation or a slide, something to explore, a true/false spot-check of your thinking, and a quick check. Every scene gives you an evidence card for your board.

How to read the scenes

  • Animation (dark teal) — a short animated explainer, one idea each
  • Slide (dark teal) — a still to study: a micrograph, a diagram or a map
  • Explore (purple) — something to push on while you watch
  • Game (purple) — a quick challenge
  • Think (gold) — reason it out, then spot-check yourself with a few true/false questions; not graded
  • Check (gold) — a quick H5P that scores itself

Scene 1 of 6

The Blood Showed Nothing

“The X-ray and the blood” came back clean — and a clean result is a true answer to the question it was built to ask.

Animation · in production · 2 min 10 s

The Blood Showed Nothing

A Saturday in 1984: an ER curtain, a nine-year-old curled on her side with her knees drawn up, a bowl, a pair of nurse’s shoes. A needle at the elbow fills one purple-capped tube. The tube tips, and what pours out is not red but symbols: the four elements that make about 96% of a body — O 65%, C 18%, H 10%, N 3% — stack into a bar, and its thin top slice splits into calcium, phosphorus, potassium, sulfur, sodium, chlorine and magnesium. A typed lab slip rolls up the screen: Na⁺, K⁺, Cl⁻, CO₂ (read as bicarbonate), BUN, glucose, a white count. Each line stamps WITHIN RANGE. The slip turns over; the back is headed NOT ON THIS SLIP and lists two blanks — a white cell’s alarm protein, a liver’s emergency protein. The words SHOWED NOTHING slide apart and re-form as SHOWED NORMAL IONS. Last frame: a big dictionary open at P.

Prefer the full lecture? Atoms, Ions, and Electrolytes (original video on the site)

Explore · in production

Decode the 1984 slip

A typed emergency-room slip on yellowed paper, with a hospital stamp, a date in 1984 and a patient line reading “Female, 9 yrs” — labeled on screen as an illustrative panel of the kind a 1984 ER ran, because canon keeps none of Stina’s values. Seven lines, each with a textbook reference range and a result column stamped WNL (within normal limits): sodium 135–145 mEq/L · potassium 3.5–5.0 mEq/L · chloride 98–106 mEq/L · CO₂, total (read as bicarbonate) 22–28 mEq/L · glucose 70–99 mg/dL (fasting) · BUN, blood urea nitrogen, about 7–20 mg/dL (adult textbook range) · white cell count, about 4.5–11 thousand per µL (adult textbook range; children run a little higher). Before tapping each line the student predicts which element it counts from a tray of tiles (Na, K, Cl, C, H, O, N, Ca). Tapping a line opens a card in three parts. WHAT IT COUNTS: sodium is element 11, counted as the cation Na⁺, the main cation outside cells; potassium is element 19, K⁺, the main cation inside cells, so the blood holds only a small, tightly kept share; chloride is element 17 as the anion Cl⁻; bicarbonate is carbon, oxygen and hydrogen as HCO₃⁻, the blood’s buffer (Chapter 2); glucose is C₆H₁₂O₆ (Chapter 3); BUN is the nitrogen in urea, a waste the kidneys clear; the white count is not a chemical at all but cells. WHAT IT REPORTS: water and salt balance, the kidneys, acid–base, fuel, and — for the white count only — infection or inflammation, which an attack can raise. WHAT IT CANNOT SEE: on every ion line, “inflammation does not make sodium” (or potassium, or chloride). A bar along the bottom fills in body composition by mass as elements are found — O 65 · C 18 · H 10 · N 3, then Ca, P, K, S, Na, Cl, Mg — with the four big ones lighting up as about 96%. A hidden eighth line appears only after all seven are opened: a blank row headed ACUTE-PHASE PROTEINS — NOT ORDERED, with a note that the liver’s emergency proteins are taught in Chapter 6 and logged in Chapter 7. Last task, rewrite the chart’s sentence: the student builds an honest one from phrase tiles (“The ions, glucose and urea measured” / “were within their reference ranges;” / “no test for inflammation proteins was ordered.”) while three decoy tiles wait (“Nothing is wrong.” · “No organic cause.” · “The pain is emotional.”). The reveal: “showed nothing” becomes “showed normal ions” — a true statement with limits. Keyboard path: Tab moves line to line, Enter opens a card, arrow keys move through the element tray and the phrase tiles, Space places a tile. A <details> text version below the slip gives every line as a plain table (line · counts · reports · cannot see) and the finished sentence.

Think · not graded

“X-ray and bloodwork show nothing.” Pick one line of a 1984 blood panel — sodium, say — and write down exactly what a normal result tells you about a nine-year-old who can’t straighten her legs. Then write what it does not tell you. Which of your two lists did the chart’s next words, “no organic cause,” come from?

The true/false spot-check for this prompt is in production.

Check · Single Choice

What must all matter have?

This self-scoring check is in production.

Evidence card 1

Add it to your evidence board

Age nine, the worst ER visit so far: “the X-ray and the blood” show nothing, and the chart reads “Recurrent abdominal pain, no organic cause.”

Scene 2 of 6

The Building Block

Protons name the element, neutrons make isotopes, electrons make ions — and every ion on an ER slip was made by moving electrons.

Narrated slide · in production · 1 min 46 s

The Building Block

Two of Amy’s narrated slides. Slide 2, Matter & Elements: matter; elements as the identities matter can take; the periodic table as “a seating chart of everything there is”; symbols as “little fossils of old Latin” — Na for sodium, K for potassium, and the kal-/calci- trap that costs points on exams; the second letter of a symbol always lowercase; the atomic number “quietly whispering about electrons — hold that thread.” Slide 3, Building the Atom: protons positive and anchored in the nucleus, neutrons uncharged beside them, electrons negative and “zipping around outside in a blur” — a fuzzy cloud, not neat planetary orbits, “however pretty the cartoon looks”; the atomic number as the element’s fingerprint (hydrogen 1, oxygen 8, sodium 11); “if a proton could simply wander off, we’d be living in a very short and very unpleasant horror movie.” Caption lines under the player: (1) Matter is anything that has mass and takes up space; charge isn’t part of the definition, and most matter is neutral. (2) The slide’s “natur-” should read natrium. (3) An atom is the smallest unit of an element that keeps that element’s properties; all three particles have been detected and measured directly — the electron since 1897, the proton since 1919, the neutron since 1932. (4) Ordinary hydrogen has one proton and no neutron.

Prefer the full lecture? Atoms, Ions, and Electrolytes (original video on the site)

Explore · in production

Three bins, one atom

A workbench with an empty nucleus in the center, a cloud ring around it, and three labeled bins along the bottom: PROTONS (+), NEUTRONS (0), ELECTRONS (−). A readout above the bench updates with every drop: Element (name and symbol, read from a seating-chart strip of the first 20 elements), Atomic number, Mass number, Charge. Round 1, protons: before each drop the student predicts what will change. One proton makes hydrogen (H, 1); a second makes helium; eight make oxygen — the element changes every single time, and the highlight slides along the seating-chart strip with it. Round 2, neutrons: with 6 protons fixed (carbon), add neutrons — 6 gives carbon-12, 7 gives carbon-13, 8 gives carbon-14; the element name never moves, only the mass number, and a tag appears: ISOTOPE. Three cards open here: carbon-14, a radioisotope used to date old material and to trace molecules in research; fluorine-18, the radioactive label on the glucose look-alike a PET scan follows (Module 1’s imaging chapter); technetium-99m, the tracer of a bone scan — the kind of scan that turns up in Stina’s adult dossier. A footnote card: ordinary hydrogen is one proton and no neutron; a periodic-table box (hydrogen 1.0080) shows why atomic masses aren’t whole numbers — they average an element’s isotopes (lithium is listed as 6.94 because most lithium has four neutrons, not three). Round 3, electrons: with 11 protons (sodium), add 11 electrons — charge 0, a neutral atom, because by definition an atom has as many electrons as protons; take one away and the readout says Na⁺, charge +1, CATION; with 17 protons (chlorine), add an eighteenth electron — Cl⁻, ANION. Trying to drag a proton out of a finished nucleus shows a padlock and Amy’s line: “a very short and very unpleasant horror movie.” One reconciliation card: H⁺ is a hydrogen atom that has lost its only electron — a bare proton, made by moving the electron, not by pulling a proton out of a nucleus (site slip N77). Final round, “Which change makes a new element?”: six cards (add a proton · add a neutron · remove an electron · add an electron · remove a proton · add two neutrons) sorted into NEW ELEMENT / ISOTOPE / ION. The reveal: only the proton count names an element; neutrons make isotopes; electrons make ions. Keyboard path: Tab to a bin, Enter drops one particle into the atom, Shift+Enter removes one; readout changes are announced in a polite live region (“6 protons, 8 neutrons: carbon-14, an isotope, charge 0”). A <details> text version lists every round as a table.

Think · not graded

Carbon-12 and carbon-14 differ by two neutrons, and your enzymes can’t tell them apart — which is exactly why a radioactive carbon can trace where a molecule goes. Why do two isotopes behave the same in a chemical reaction? Which particles does chemistry actually use, and what single change would turn carbon into a different element?

The true/false spot-check for this prompt is in production.

Check · Drag the Words

Sort the particles and the counts that name an atom. Two distractors are on the bank.

This self-scoring check is in production.

Evidence card 2

Add it to your evidence board

“They did the X-ray and the blood”: the chart records two tests as done and clean, and nothing about what the blood test counted.

Scene 3 of 6

Full Shells Win

A peanut M&M, two preferences of the universe, and the one shell where everything social about an atom happens.

Narrated slide · in production · 2 min 00 s

Full Shells Win

Amy’s narrated slide, Where Electrons Live: “an atom is a peanut M&M. The peanut is the nucleus, you dip it in chocolate to make the first shell, dip it again for the second” — nested three-dimensional spheres, even though we’re forced to draw them flat. “Tattoo the universe’s two preferences onto your brain: shells like to be full, and electrons like to be in pairs.” The first shell holds 2; the shells after it hold 8 — “for us, it’s going to be three layers… and then after that we don’t care, at least for this class.” Oxygen’s 8 electrons: 2 fill the first shell, six are “stranded in a second shell that has room for eight” — easier to borrow or share two than to rehome six, “like trying to rehome six kittens versus giving away one. Nobody wants them.” The valence shell, the outermost, is “the only one that decides how an atom will behave — everything social about an atom happens there.” Caption line under the player: the 2-8-8 rule holds for the first 20 elements, through calcium — everything A&P needs.

Prefer the full lecture? Atoms, Ions, and Electrolytes (original video on the site)

Explore · in production

Stack the shells

Eight atoms wait on a shelf, each a bare nucleus with its proton count printed on it: H (1), C (6), N (7), O (8), Na (11), Cl (17), K (19), Ca (20). Pick one and it moves to the center of three nested rings drawn as a cut-open peanut M&M — a peanut nucleus, a thin first chocolate shell, two thicker ones — with a fourth faint ring that appears only when it’s needed. Electrons drop one at a time from a hopper; the student places each in a shell slot. The shells refuse an electron in an outer ring until the inner one is full (2, then 8, then 8), and the slots on each shell fill singly before they pair up — the universe’s two preferences, enforced. When the count matches the protons, the atom locks and asks for a prediction before anything else happens: will it GAIN, LOSE or SHARE electrons, and how many? Then the reveal animates it. Na (2-8-1) loses one and becomes Na⁺. K (2-8-8-1) — flagged as the atom that needs a fourth ring, “past three layers, where we stop caring” — loses one and becomes K⁺. Ca (2-8-8-2) loses two and becomes Ca²⁺, the ion Module 1’s calcium loop defends. Cl (2-8-7) gains one and becomes Cl⁻. O (2-6) gains two or shares two pairs. N (2-5) shares three. C (2-4) shares four. H (1) shares one — or loses its only electron and becomes H⁺, a bare proton, the particle that will define pH in Chapter 2. A score card keeps the student’s predictions against the reveals, and a kitten counter shows the cost of rehoming: giving away one is easy; six, nobody wants. Last screen: all eight atoms side by side, sorted by what their valence shell made them do, under one line — full shells win. Keyboard path: Tab to an atom, Enter brings it to the center, arrow keys choose a shell, Space places an electron; predictions are a radio group. A <details> text version gives each atom’s shell filling (Na 2-8-1, and so on) and its outcome in a table.

Think · not graded

Sodium has one electron in its outer shell and chlorine has seven. Using only the two preferences — shells like to be full, electrons like to be in pairs — explain why sodium ends up positive and chlorine negative, and why neither one simply sheds or grabs six or seven electrons instead.

The true/false spot-check for this prompt is in production.

Check · Fill in the Blanks

Two preferences run all of this chemistry: shells like to be full, and electrons like to be in pairs. Fill in each blank.

This self-scoring check is in production.

Evidence card 3

Add it to your evidence board

“I couldn’t straighten my legs”: the worst attack so far, and the ER’s reading of it — pain with “no organic cause.”

Scene 4 of 6

Give One, Take One

No hand-holding here: one atom donates, one accepts — and the salt that results lets go the moment it meets water.

Narrated slide · in production · 1 min 48 s

Give One, Take One

Amy’s narrated slide, Transfer: one atom donates, the other accepts — then they attract, and that attraction is the bond. Mostly salts, like Na⁺ and Cl⁻. Table salt is “the textbook romance — there’s no genuine hand-holding here, no shared anything, just two oppositely charged ions standing close because the charges won’t let them drift apart.” A strong bond on a dry shelf, “which can fool you”: “rock-solid in the salt shaker, but the moment it hits water it lets go. Context is everything.” The ions from dissolved dietary salt are what “fire a thought down a nerve or clench a muscle” — or wiggle a big toe. Caption line under the player: in the watery body, covalent bonds are the strongest; ionic bonds let go in water (site slip 21).

Prefer the full lecture? Covalent Ionic and Hydrogen Bonding (original video on the site)

Explore · in production

Pull the rope

A rope stretched across a tug-of-war field between two atoms; the electron or electrons at stake ride on the rope as bright beads. A pair picker offers six matchups: Na vs Cl · K vs Cl · Ca vs Cl (a second chlorine waits on the sideline) · H vs H · O vs H (played twice) · Na vs Na. Before each pull the student predicts the outcome: the bead goes all the way across (transfer), stops in the middle (equal sharing), or stops closer to one side (unequal sharing). Then the pull plays. Na vs Cl: the bead crosses and stays; the atoms become Na⁺ and Cl⁻, and the student types the charges and the formula, NaCl, using on-screen superscript and subscript buttons. K vs Cl: the same, KCl — with a side card naming K⁺ for its later job: the main cation inside every cell, kept there by the sodium-potassium pump (Module 3); when it leaks out of a stressed white cell it trips a different alarm sensor, NLRP3 — pyrin is set off another way. Ca vs Cl: calcium has two to give, one chlorine can take only one, so the second chlorine steps in and the student writes CaCl₂ (Ca²⁺ — the ion Module 1’s calcium loop defends; named only). H vs H: the bead stops dead center — a shared pair, H₂, the covalent bond of Chapter 2. O vs H: the bead slides toward oxygen but doesn’t cross; play it on the other side too and the student writes H₂O with δ− and δ+ marks — a preview of “lopsided,” Chapter 2. Na vs Na: nobody wins and nothing forms — a deliberate no-bond card. A scoreboard tallies TRANSFER / SHARE EQUALLY / SHARE UNEQUALLY, and a rule panel adds the charge check from Amy’s ions group activity: the charges in an ionic formula must add to zero, cation written first. The reveal: ionic versus covalent is a question of how hard each side pulls, and a salt is a lattice of ions only until water pries them apart. Last card: drop the NaCl crystal into a glass of water and watch the ions float off — dissociation, the next scene. Keyboard path: Tab to the pair picker, Enter chooses a pair, Space pulls; the charge and formula boxes are text inputs. A <details> text version lists each pair, its outcome, the charges and the formula.

Think · not graded

Table salt is “rock-solid in the salt shaker,” yet it falls apart the moment it hits water. If ionic bonds come undone that easily in water, why does it matter that sodium and chlorine form a salt at all — and what does your body actually use once the salt has dissolved?

The true/false spot-check for this prompt is in production.

Check · Drag the Words

Build the ionic bond from transfer to dissociation. Two distractors are on the bank.

This self-scoring check is in production.

Evidence card 4

Add it to your evidence board

“I threw up on the nurse’s shoes and I’m sorry about that”: the one line from the 1984 visit that records what her body lost.

Scene 5 of 6

Salts That Conduct

You are an electrical creature: wiggle your big toe, and ions just carried the order.

Narrated slide · in production · 1 min 47 s

Salts That Conduct

Amy’s narrated slide, Ions at Work: “you, improbably, are an electrical creature. Wiggle your big toe right now” — electricity just shot down your spine and out your sciatic nerve, “and that current is not a metaphor.” It runs on ions in blood, interstitial fluid and cytoplasm; “lose control of those ions and the whole electrical you goes dark.” Dissociation; strong electrolytes (table salt splits completely), weak ones (only partly), and non-electrolytes such as an alcohol, which dissolve but stay intact; “the body cares intensely about exactly how many free ions are floating in its fluids at any given second.” Figure: three flasks — non-electrolyte, weak, strong. Caption lines under the player: (1) Salts dissociate the moment they dissolve — in the mouth, the stomach, the gut — and are absorbed as ions, not split “on arrival in the bloodstream.” (2) Electrolytes are salts, acids and bases; clinically, the word names the ions themselves (Na⁺, K⁺, Cl⁻, HCO₃⁻, Ca²⁺). (3) A nerve impulse is ions crossing membranes, not electrons running down a wire.

Prefer the full lecture? Atoms, Ions, and Electrolytes (original video on the site)

Explore · in production

Light the bulb

A conductivity tester on a lab bench: a battery, a light bulb and two metal probes dipping into a beaker of distilled water (bulb dark). A shelf of eight samples: a dry salt crystal · table salt (NaCl) stirred into water · calcium chloride (CaCl₂) · potassium chloride (KCl) · table sugar (sucrose) · urea (the waste a BUN line counts) · dilute hydrochloric acid (the acid of the stomach) · vinegar (acetic acid) · vegetable oil. Before each test the student predicts BRIGHT, DIM or DARK. Add a sample and three things happen: the bulb lights (or doesn’t) on a brightness meter; a zoom window shows what’s in the water — NaCl as separate Na⁺ and Cl⁻, CaCl₂ as one Ca²⁺ and two Cl⁻, sugar and urea as whole molecules, vinegar as mostly whole molecules with a few ions, oil as a layer that never mixed; and a particle counter reports how many particles one formula unit made (NaCl → 2, KCl → 2, CaCl₂ → 3, sugar → 1, urea → 1). The dry crystal is the opening trap: probes on a dry crystal, bulb dark — the ions are locked in place, which is why a salt shaker never shocks you. The reveal sorts the shelf into STRONG ELECTROLYTE (NaCl, KCl, CaCl₂, HCl — acids and bases count, not only salts), WEAK (vinegar), NON-ELECTROLYTE (sugar, urea — dissolved but uncharged) and DOESN’T DISSOLVE (oil). A side panel explains the lab’s unit: milliequivalents per liter count charge, so a millimole of Na⁺ is 1 mEq but a millimole of Ca²⁺ is 2 mEq — “the number carries the message,” and concentration is the difference between normal and alarming. The particle count (2 versus 3) returns in Module 3 as osmosis. Last card, the big-toe line: every signal down a sciatic nerve is ions moving through membrane channels, which is why an ER panel guards sodium and potassium so closely. Keyboard path: Tab to a sample, Enter adds it, R rinses the beaker; the bulb’s state is announced (“bright — strong electrolyte”). A <details> text version gives the full results table.

Think · not graded

Glucose dissolves in plasma as easily as salt does, yet it never lights the bulb. What is the difference between dissolving and dissociating — and why would an ER worried about a child’s nerves and heart measure her potassium for that purpose, but not her sugar?

The true/false spot-check for this prompt is in production.

Check · Single Choice

In A&P we call dissolved ions electrolytes. Why does the body hold them within tight limits?

This self-scoring check is in production.

Evidence card 5

Add it to your evidence board

The same day the blood came back in range, the visit moved on — the doctor’s long talk with Mom in the hall ended with the word psychiatrist.

Scene 6 of 6

On the Nurse’s Shoes

One bout of vomiting carries out water, acid, chloride and a little potassium — and a body can still read normal an hour later.

Animation · in production · 2 min 00 s

On the Nurse’s Shoes

Nurse’s shoes on an ER floor, and a small splash. A cutaway stomach, its acid drawn as a yellow pool, empties upward, and labeled particles leave with it — water, H⁺, Cl⁻ and a few K⁺ — while a second panel shows the same nine-year-old’s blood as five needle gauges with textbook reference bands: Na⁺ 135–145, K⁺ 3.5–5.0, Cl⁻ 98–106, HCO₃⁻ 22–28 (mEq/L) and glucose 70–99 mg/dL. After one bout the needles twitch and stay inside their bands: fluid from between her cells refills the blood, and two kidneys, drawn as adjustable valves, hold back sodium and water. A fast-forward strip — a whole day of vomiting, nothing to drink — and the needles start to lean: chloride and potassium slide low, bicarbonate climbs (a label, TOWARD ALKALOSIS, locks with MODULE 20). Back to Saturday: every needle in its band, the slip stamped WITHIN RANGE, and beside it a thermometer and a white cell that the ion bands cannot register. A last card dated 2006: two IV bags on a pole — “They hung two bags of fluid” — age thirty-one, a story for later.

Prefer the full lecture? Atoms, Ions, and Electrolytes (original video on the site)

Explore · in production

Before and after

Two panels side by side, BEFORE and AFTER, each a stack of five needle gauges with the textbook reference band shaded — Na⁺ 135–145 mEq/L · K⁺ 3.5–5.0 mEq/L · Cl⁻ 98–106 mEq/L · HCO₃⁻ 22–28 mEq/L · glucose 70–99 mg/dL — plus a beaker showing total body water. The whole thing is labeled as a model with textbook ranges, not Stina’s values, which canon does not keep. Three sliders drive the AFTER panel: HOW MUCH WAS VOMITED (one bout · several · a whole day), HOURS SINCE (0 · 2 · 12 · 24) and DID SHE DRINK? (nothing · sips · enough), plus a KIDNEYS ON/OFF toggle. Before every move the student predicts which needle will move first. The model’s rules sit beside it in plain words: vomit is stomach contents — water, plus H⁺ and Cl⁻ from hydrochloric acid, and some K⁺; losing H⁺ leaves bicarbonate behind, so HCO₃⁻ creeps up (labeled “toward alkalosis,” with a lock: Module 20 explains it); fluid from between the cells refills the blood within the first hour; the kidneys, when on, hold back sodium and water, and over many hours of vomiting they end up wasting potassium too. One bout, two hours, sips: every needle stays in its band and the beaker barely dips — the panel reads normal. A whole day, nothing to drink: chloride and potassium slide below their bands (hypokalemia is below 3.5 mEq/L; hyponatremia below 135, hypernatremia above 145 if water loss outruns salt loss), bicarbonate rises above its band, the beaker drops, and a card appears: THIS IS WHY VOMITING PATIENTS GET IV SALINE — 0.9% NaCl, often with KCl added. Turn the kidneys off and even the mild case drifts — the reveal that “normal” was never passive; it was being held. A final strip adds a thermometer at 39 °C and a white-cell counter, and asks the student to find any slider that makes an ion needle report inflammation. None does. Closing sentence to complete: “Electrolytes measure ______, not ______.” (balance; inflammation). Keyboard path: the sliders are native range inputs with labeled steps; every needle move is announced in a live region in words (“Chloride: below range”). A <details> text version gives the model’s rules and a table of six scenarios and their results.

Think · not graded

A nine-year-old vomits once in the ER, and two hours later her sodium, potassium, chloride and bicarbonate are all inside their reference ranges. Name three things her body did in those two hours to keep them there. Then explain why a normal panel after vomiting is evidence that her kidneys work — and not evidence about what made her vomit.

The true/false spot-check for this prompt is in production.

Check · Single Choice

A child vomits once in the emergency room, and her electrolyte panel comes back within range. What is the best reading?

This self-scoring check is in production.

Evidence card 6

Add it to your evidence board

Vomiting at the worst ER visit, a panel that came back clean, and no IV in the diary — her first bags of fluid wait until she is thirty-one.

4

Your evidence board

Every scene gave you an evidence card, and the chart adds more. Sort each card into the column it supports: Normal ions, an unasked question, Neither on its own, or No organic cause. Some cards can honestly go in more than one place — that’s allowed, and the feedback tells you which cards decide the case.

Evidence board · drag and drop · in production

The sorting board for this chapter’s cards is being built. Until it arrives, sort your evidence cards on paper into the three columns above.

5

Your verdict

Time to decide. Look back at your bet, then build your verdict from statements that hold up — no writing needed.

Look back at your prediction

A belly attack so bad she couldn’t straighten her legs, vomiting, and blood that “showed nothing” — read through atoms and ions, the reading that fits best is…

Find the one you chose at the top. Does the evidence support it, refute it, or revise it?

  • Nothing was wrong — “Recurrent abdominal pain, no organic cause”
  • She was upset and it settled in her stomach — “a bright, sensitive girl”
  • The numbers that were measured came back in range, and they measured something other than inflammation

Build your verdict · no writing

Choose the statement that holds in each set. The ones you keep become your argument.

This activity is in production.

6

The finding

Finding · atoms and ions

The Blood Showed Normal Ions

1984, age nine: the worst belly attack so far — legs she couldn’t straighten, vomiting in the ER, “the X-ray and the blood” — and a chart that read “Recurrent abdominal pain, no organic cause. Psychiatry referral.” Chart entry: the blood test of the day counted ions, a sugar, a waste product and cells; ions are atoms with electrons moved, held in narrow ranges by the kidneys and the body’s fluid reserves, and one bout of vomiting rarely moves them — so “showed nothing” means “showed normal ions,” a true answer to a question about balance, not about inflammation. Held open: what an inflamed belly does put into the blood — the liver’s acute-phase proteins (Chapter 6) — and Chart Clue #2, across these years (Chapter 7).

Next · Chapter 2

Water, pH and the Buffer

Eleven: a fever of 103, “they took blood,” the Tylenol and the bucket on a cool bathroom floor — and a blood pH that almost certainly held near 7.4 the whole time. Water and its buffer are the chemistry that never left the room.

Continue to Chapter 2 →

Reliable information on rare diseases

NORD · NIH GARD · Orphanet · MedlinePlus Genetics: FMF · FMF & AID Global Association · Autoinflammatory Alliance · Global Genes · Amyloidosis Foundation

Stina has one rare disease. In the United States, about 1 in 10 people live with one of the more than 7,000 known rare diseases. These organizations are where patients, families and clinicians go for trustworthy information.

Hop to:

← Familial Mediterranean Fever — case home

All pages for Module 2 — Just Enough Chemistry

2.0 Module Overview
2.1 Atoms, Ions, Electrolytes
2.2 Water, pH and the Buffer
2.3 Carbohydrates and Energy
2.4 Lipids: Membranes, Steroids and the Lipoprotein Fleet
2.5 Proteins: Shape Is Everything
2.6 The FMF Molecule Cast
2.7 Misfolding: From Pyrin to Amyloid
2.8 Conclusion and Assessment
2.9 Evidence Behind the Case

All Modules
  1. Anatomical Language, Membranes & Homeostasis
  2. Just Enough Chemistry
  3. The Cell & Its Transport
  4. Making Cells & Proteins
  5. The Integumentary System
  6. The Skeletal System
  7. The Muscular System
  8. Nervous Tissue & the Senses
  9. The Spinal Cord
  10. The Brain & the Blood–Brain Barrier
  11. The Autonomic Nervous System
  12. Special Senses (in development)
  13. The Endocrine System
  14. Blood
  15. The Heart
  16. Blood Vessels
  17. The Digestive System
  18. The Respiratory System
  19. The Urinary System
  20. Fluids, Electrolytes & Acid–Base Balance
  21. The Reproductive System
  22. The Immune System

List of terms