3.3 Atomic Number

... Meanwhile, Spruce continued to talk to himself.  "It's the protons that tell you what element it is.  That's because it's the only particle whose number is always the same no matter what form the element comes in."

Stefanie carefully removed a piece of parsley from a delicious strip of fettuccine.

"You see, we normally think an atom has the same amount of protons and electrons.  When it does, it has no charge or a neutral charge.  The negatives of the electrons outside the nucleus balance out the positives of the protons in the nucleus."

Stefanie next eyed a strip of fettuccine with some extra Alfredo sauce on it.  It looked absolutely delicious.

"But some atoms can give away some of their electrons or borrow some from another atom.  When that happens, the atom can become an ion with either a positive or negative charge.  So you can't count the electrons to decide what kind of an atom it is.  The number can change."

"That's interesting," Stef said, eyeing a lovely bit of broccoli.

"You can't count the neutrons," Spruce continued, "because the same element can come with different numbers of neutrons.  They're called different isotopes of the element."

"What's an element again?" she asked, not noticing that Spruce had used the word repeatedly.

"An element is a kind of atom.  So gold is an element, a particular kind of atom.  Silver is an element, a particular kind of atom."

"And diamonds are a kind of atom," she said.

"No, I think diamonds are made up of carbon atoms or something."

Oooo, Stef thought, a mushroom.  It had been hiding under several fettuccine noodles.

"So that's why they use the number of protons to identify an atom, because if you change the number of protons, you've changed the kind of element."

With no more fettuccine, broccoli or 'shrooms on her plate, Stef finally was forced to look at him.

"And I need to know this why?"

"The number of protons in an atom tells you the atomic number," Spruce answered. "It tells you which element it is.  You know the periodic table, that chart on the inside of every chemistry book?"

"Yeah?" and indeed she did.  There had been a huge one in her high school chemistry room, a picture full of boxes stacked on top of each other, like you were looking through the walls of some huge condominium with a tower on each end.

"The periodic table starts at the top left with the number 1 and moves across each row with the atomic number counting up one by one.  The first row only has two boxes on each end, numbers 1 and 2."

"So you're telling me number 1 has one proton in its nucleus and number 2 has two protons in its nucleus?"

Spruce was actually surprised she had paid that much attention.

"Yeah, hydrogen has one proton and helium has two.  Then the next row keeps counting up: 3, 4, 5, 6, 7, 8, 9, 10."

"Why does it skip the space in the middle at the top," Stef surprisingly asked, having stared at the chart a time or two in high school.

Spruce thought like he was about to say something profound and finally came forth with his answer.  "No idea"...