States of Matter

Imagine this.  You, Dustin, and Democritus continue for a ways down the dusty road, with the walls of Abdera slowly rising before you.  It is late afternoon, and the sun is hot, but you don’t notice.  You are hung up on a question.  

You look at Democritus and begin, “You said that everything is made of atoms.”

“Yes,” he says.

“But I see a leaf over here and a stone over there.  You are thinking that they are made from the same thing, but a leaf is very different from a stone.  How is that possible if everything is made from the same thing?”

A broad smile spreads beneath Democritus’ gray beard.  “Now that is an excellent question.”

“What is the answer?” Dustin asks.

“I do have some guesses,” Democritus says.  He stops and crouches beside the road, sweeping his palm across the dust until he has made a smooth patch of earth.  With a finger he begins drawing several small circles.  “I think there are different kinds of atoms.  I think they might come in different shapes and sizes.”  Beside the circles, he draws several crooked shapes, and then sharp, jagged ones.  Some have little hooks extending from their sides.  “Perhaps some atoms are round like these,” he explains.  “And maybe there are others like these, that are rough, pointed, curved, or hooked.”

Dustin kneels beside him. “Is that what atoms really look like?”

“Well, remember that I have never seen an atom,” Democritus says, “so I can’t be sure that is what they look like.” 

You kneel on the other side of the drawing.  “Then why do you think they might have these different shapes?”

“Because the things they form behave in different ways,” Democritus says.  “Shouldn’t that tell us something about the behavior of the atoms that form those things?  It is kind of like each type of atom has its own personality, its own way of moving and interacting with other atoms.  That personality is reflected in the things that those atoms form.”

“A personality?”  Dustin asks.  Pointing to one of the hooked atoms, he asks, “Is that one angry?”

“Why would it be angry?”

“It looks angry.”

Democritus considers the drawing.  “It does look rather unpleasant.”

“And that round one looks friendly,” Dustin continues.

“That is not quite what I mean by personality,” Democritus says, smiling.  “Atoms do not become cheerful or angry.  I mean that they have ways of behaving.  Some may catch and hold on to others.  Others may roll or slide past each other.  If we observe closely the matter around us, I think we can begin to gain some sense of the personalities of the atoms that make up that matter.”

Democritus picks up a stone and places it into your hands.  “Tell me about this,” he says.  “What do you notice about it?  What is it like?”

“It’s a rock,” Dustin says.

“Thanks, Dustin,” you say, rolling your eyes.  You are pretty sure that Dustin is made up of irritating atoms, but you keep that thought to yourself.  You turn the stone over in your hands and run a finger along its edge.  Then you begin to describe it.  “Well, it’s gray, with maybe some black splotches.”

“Okay,” Democritus says.  “What else?”

“Its surface is rough and jagged,” you continue.  “And it is hard.  I can press it between my hands, but it doesn’t crack.”

Democritus points to his drawings on the roadside.  “So I have drawn different types of atoms in the dirt here.  Which of these would you guess make up a rock like that one in your hands?”

“Probably those ones,” Dustin jumps in, pointing at a group of atoms with jagged edges and hooks.

“Why those?”

“Because they are jagged like the rock,” Dustin says.

You consider your answer carefully, and then say, “It is reasonable to think that stones are made from atoms that are packed together and bonded tightly.  Those ones that Dustin pointed at seem like they might do that.  Those hooks would maybe catch on to each other and make it hard to break those atoms apart.”

Democritus nods.  “That is what I think, too.”  Then he pulls a small flask from his bag.  He removes the stopper from the top and pours a little water into your cupped palm.  “Now tell me about this.  What is this like?”

You look over at Dustin, ready for him to blurt an irritating comment, but he remains silent.  You look closely at the pool of water in your hands.  “It fills my hand,” you begin.

“What do you mean by that?” Democritus asks.

“When I cupped my hand, it made a little hollow at the bottom, and all the water went into that hollow and filled it.  It’s kind of like the water changes shape to fit my hand.”

“Interesting,” Democritus says.  “Is that different from the rock?”

“Yes, the rock didn’t change shape in my hand.”

Then you tilt your hand and watch as water slips between your fingers and falls onto the dusty road.

“That is another difference from the stone,” you say.  “The water squeezed between my fingers.  It flowed.  The stone didn’t do that.”

Democritus points to his drawing.  “So which of these might be like water atoms?”

“Maybe those ones,” you say, pointing to a line of round, smooth atoms.  “If they are round, perhaps they roll over and slide past one another.  That would explain why they flow and change shape.”

“Like a pile of little balls,” Dustin adds.  Just then, a gust of wind sweeps across the road.  It lifts dust into the air, tugs at Democritus’ cloak, and sends several dry leaves tumbling past your feet.  Dustin turns his head too late and catches some of the dust in his face.

“Can you feel the air?” Democritus asks, looking at the dust swirl about.

Dustin sputters and rubs his eyes.  “Definitely.”

You feel it as well.  The breeze presses against your face, moves through your hair, and pulls at your clothes as it flows by.

“Doesn’t the wind seem to move like the water?” Democritus asks.  “It flows past us just as the water flowed between your fingers.”

Democritus turns back to his drawings.  He points to a third group, near the pack of tightly hooked atoms and the line of smooth circles.  These atoms are scattered widely, with large spaces between them.  Lines in the dust show them moving in different directions.  “Perhaps the atoms in air are like this,” he says.  “They do not remain packed closely like the atoms in the stone.  They do not gather and flow together as I imagine the atoms in water do.  They spread apart and move freely around things, filling whatever open space they find.”

You examine the three pictures in the dust.  Three familiar names begin to make sense.  “That is a solid,” you say, pointing to the first group of atoms, tightly packed and hooked together.  “That is a liquid,” you continue, pointing to the second group, the line of smooth and rounded atoms, sliding past one another.  You point at the third group, atoms bouncing far and wide, moving freely through space.  “That is a gas,” you say.  “Solid, liquid, and gas.  Three forms of matter,” you conclude.

Democritus flashes a big smile.  “Those are three useful names for three different ways matter behaves.”

“And the forms are different because their atoms have different personalities?” Dustin asks.

“That’s what I think,” Democritus says.  

Dustin points to the stone. “Those atoms cling tightly.”

“So I imagine.”

He points toward the spilled water. “Those stay close, but roll around each other.”

“Seems like it.”

“And the atoms in air bounce around and fly everywhere.”

“That is my guess.”

Dustin smiles. “I think we figured it out.”