Two Atoms Make a Molecule

A/N: This is a long overdue post-ep fic that I owed webuiltthepyramids. We both wanted to see Leonard teach Penny physics after watching The Gorilla Experiment, and it fell to me to write it (in exchange she wrote about Leonard seeing Penny's psychic). I'm sorry this wasn't completed sooner, hon! I kept getting the wrong Leonard and Penny stuck in my head. :(


Penny burst into her apartment, furious. Stupid Sheldon and his stupid, sucky way of teaching. God she was such an idiot! Penny plopped down on the couch and buried her face in her hands. Hot tears of rage and embarrassment threatened to spill over, but she dug her wrists into her eyes to stop them. She heard the door open, but didn't look up. She knew who it was.

Leonard hesitated once inside. Honestly, he was a bit bemused by the situation. He wasn't exactly certain of what had transpired between Sheldon and Penny, but he knew it somehow had led to Penny memorizing that speech she had just made. He equally knew that Penny had had no idea what any of it meant until Howard pointed it out. After which, Penny had promptly punched Sheldon in the arm and stormed out. Now here he was trying to figure out what to say to his, obviously upset, girlfriend.

"You know, I don't think Sheldon's going to be able to use that arm for about a week." Penny rolled her eyes as she shifted to be curled up in the far corner of the couch. She still wouldn't look at Leonard. He sighed and sat down on the couch by her feet.

"May I ask how Sheldon got you to say all those things?" Penny furrowed her eyebrows and frowned. She considered lying or simply not answering, but then figured Leonard had to already think she was an idiot so she might as well tell him the truth.

"I asked Sheldon to teach me about physics, but I didn't get any of it because I'm stupid so he just had me memorize that speech instead," she answered despondently. Leonard's eyebrows shot up. Whatever reason he was expecting to hear, it wasn't that.

"Hold on. You wanted Sheldon to teach you physics?"

"Yes." Penny sighed. Leonard frowned, confused and a little bit hurt that she hadn't asked him to teach her.

"But, why?"

Penny closed her eyes. "Because I wanted to surprise you and be able to talk about your work with you. But I failed because I'm a complete idiot!" She got up suddenly and started pacing the apartment. Leonard stood up too.

"Penny, what? Hey, stop it." He tried catching her arm, but Penny swerved and avoided him. "Penny, will you come here! Look at me okay? Just look at me." Penny finally stopped and raised her eyes to meet his. Leonard walked over, took her hand, and said firmly. "Now listen to me. You are not an idiot."

Penny bit her lip. "Sheldon called me stupid."

"Sheldon calls everyone stupid, remember? Me included."

"But he couldn't teach me anything."

"Penny, he once made a grad student so nervous, they threw up. He's not really the best instructor." Penny let out a shaky breath, but she didn't look very reassured. Leonard tried a different direction. "You know, I could teach you about physics."

Penny raised an eyebrow. "Really?"

Leonard shrugged. "Sure, of course! That is, I mean, if you're still interested." He looked at her hopefully.

"You're not going to start with ancient Greece, are you?"

Leonard was thrown off by the question. "What? No! What does Greece have to do with anything?"

Penny breathed a huge sigh of relief. "I don't know, but I don't want to find out." She looked back at Leonard. "So you'll really teach me physics?" Leonard's face lit up.

"Uh, huh. Where do you want to start?"

Penny thought for a second and asked quietly. "What's a subatomic particle?" Leonard smiled. He guided her back to the couch, opened up a notebook, and began walking her through the basics of an atom. Much to Penny's surprise and relief, she was able to follow most of it. Whatever she couldn't understand the first time, Leonard patiently clarified and re-explained until she did understand. Penny decided Leonard was a much better teacher than Sheldon. His reward system was a lot better too.

*** Epilogue! ***

"Antielectron neutrino, antimuon, antimuon neutrino, antitauon, antitauon neutrino, bottom antiquark, bottom quark, charm antiquark, charm quark, down antiquark, down quark, electron neutrino, muon, muon neutrino, ..."

"ERRRNNNN!" Howard interrupted, staring at a sheet of paper.

"What? What part of that was wrong?"

"You forgot electron." Penny supplied, not looking up from her food.

"Yep! You said 'electron neutrino' but didn't say 'electron' before it," Howard said. He gloated while Sheldon sputtered incoherently.

"Hold on!" Sheldon shouted. "How did she know that? She didn't even have the cheat sheet in front of her!"

Howard and Raj frowned and everyone turned to look at Penny. She paused her eating and looked around confused.

"What?" she asked with her mouth full of food.

"How do you know all the fermions in alphabetical order?" Sheldon demanded in an accusatory tone.

Penny looked at him weird and swallowed. "I don't. I just know you skipped electron."

"But, but, HOW?!"

"If I were you, I'd be more concerned with how you managed to forget 'electron'," Leonard interjected.

"Yeah, no kidding, Sheldon. Electron is one of the basic particles. Even I remembered it," Penny added with a smirk.

"Excuse me, but do you even know what an electron is?" Sheldon asked in annoyance. Penny shot him a whithering glare.

"Yes, as a matter of fact, I do! An electron is the tiny particle that spins around the nucleus of an atom. It has a negative charge and can be found anywhere within the 'cloud' surrounding the nucleus, but is most likely going to be in certain rings like that guy Bohr said. Each ring can only have a certain number of electrons and that number increases as you move farther from the nucleus. And whether the outer ring is full or not determines if the atom can get involved in a chemical reaction. So there!" Penny finished by sticking her tongue out. Sheldon's, Raj's, and Howard's jaws had all fallen to the floor in shock. Penny grinned really big. "Leonard's been teaching me physics," she said, turning to look at him. Leonard smiled proudly back at her, and they both chuckled over managing to leave the guys speechless.

Penny leaned back towards Sheldon. "You should shut your mouth, sweetie, before a bug flies in."