Seeing that everyone had arrived, Li Dong stood up and cleared his throat, trying to act like a grown-up.
"Well, today is a rare occasion for us all to be together, so we..."
He’d meant to start with some impressive-sounding pleasantries, but he realized halfway through that he had no idea what to say.
The other four just stared at him.
Li Dong braced himself for a couple of seconds, but he couldn’t think of anything. He broke the silence with a laugh.
"Hey, it’s nothing important. I just didn’t expect you all to still be at school instead of going home for the break."
He was genuinely surprised that Qi Yu and Gu Ming hadn’t gone home either.
So Li Dong figured he might as well invite them all at once. It would save him some trouble.
Once all the dishes were served, the atmosphere relaxed.
Halfway through the meal, Li Dong put down his chopsticks and turned to Gu Ming.
"Gu Ming, there’s something I might need your help with."
Gu Ming had already figured it out. This meal wasn’t about recruiting him for a project group, and he was a little disappointed.
But since East God was the one asking, he still replied.
"You’re being too polite. Just tell me what you need."
Li Dong gestured toward Wang Hao beside him.
"My roommate here plans to enter the National Mathematical Modeling Competition this September, and he’s still looking for one more teammate."
"I was wondering if you might be interested."
Gu Ming froze for a second, then quickly ran through his summer schedule in his head.
His materials for the summer camp were more or less ready, and his paper’s first draft was already on its third revision. All that was left was to schedule meetings with professors and interview at a few schools.
He was definitely busy, but he could probably squeeze in the three days and three nights required for the competition in September.
Besides, he’d wanted to do the modeling competition for a while now. He’d only held off because he could never find reliable teammates.
Now, Li Dong was essentially handing him a teammate on a silver platter.
"Alright, no problem," Gu Ming said, nodding.
At this, Wang Hao stood up as well.
"Gu God, we’ll be counting on you, then!"
Gu Ming quickly waved his hands in dismissal.
"Whoa, whoa, whoa, enough with the ’God’ stuff. In front of East God, how could I dare call myself that?"
The two of them then started discussing training details.
With that matter settled, Li Dong tuned them out.
As far as he was concerned, his mission for the day was complete.
He then noticed Qi Yu across the table, who was slurping away at the Spicy Boiled Beef.
The spice had made the tip of her nose a little red and her eyes slightly watery, but her chopsticks hadn’t stopped for a moment.
Li Dong grabbed a napkin and passed it to her.
"Qi Yu, are you allergic to spicy food?"
Qi Yu nodded, taking the napkin to wipe her nose.
"A little, but I think it tastes great."
Li Dong gave her a thumbs-up. "Great minds think alike."
He paused, then added, "But you could try eating a little slower. The faster you eat, the spicier it feels."
Qi Yu smiled.
"I was in a meeting until six and didn’t have time to eat. I’m starving."
"What kind of meeting?" Li Dong asked casually.
"For the summer camp paper proposal," Qi Yu replied, popping a piece of beef into her mouth.
Li Dong’s interest was piqued, so he asked.
"What’s the topic?"
Qi Yu put down her chopsticks, considering how to explain it in the simplest terms.
"Simply put, it’s about figuring out what element an atom is on a single-atom level."
She took a napkin, pulled a pen from her bag, and sketched a sharp tip pointing at a row of small circles.
"You’ve probably heard of the Scanning Tunneling Microscope, or STM."
"It can see the position of individual atoms with atomic resolution, but it has a critical weakness. It can see *that* there’s an atom, but it can’t tell you if that atom is iron, copper, or gold."
Li Dong raised an eyebrow.
’Okay, I get that,’ he thought.
"So, for a long time, if you wanted to know what element a specific atom was, you had to rely on chemists to pre-design the sample."
"For example, they’d deliberately spread a certain element very sparsely, then work backward and say, ’Hey, that bump in the image must be it.’"
Qi Yu shook her head.
"That method is neither rigorous nor universally applicable."
She added a diagonal line to the napkin, representing an X-ray.
"What we want to do is introduce synchrotron X-rays and directly obtain an atom’s X-ray absorption spectrum on the single-atom scale."
"Every element has its own unique absorption edge."
"Iron has its own, copper has its own, terbium has its own—just like how everyone’s fingerprint is different."
She looked up at Li Dong.
"If we can capture that fingerprint signal on the single-atom scale..."
"...then we can look at an STM image and tell you, atom by atom: this is this element, this is its chemical valence state, and this is what its electronic structure looks like."
Li Dong nodded.
Qi Yu continued.
"Research groups abroad have already made progress down this path, so we’re not starting from scratch."
"Instead, we’re building on their foundation, using a type of transition metal supramolecular assembly as our sample. We’re designing a concrete method that we can reproduce in our own lab, with the final goal of applying it to a single-atom catalysis system."
"For the summer camp, designing a practical methodology like this is a huge plus."
When she finished, she looked up, curious to see if this junior, who was supposedly a math whiz, had been completely lost by her explanation.
But Li Dong just let out a soft, "Oh."
In that instant, however, Qi Yu saw a flicker of light in his eyes.
Because the moment she said, "Every element has its own unique X-ray absorption edge," and, "It’s the atomic fingerprint of an element..."
...Li Dong thought of something.
He thought about the topic Madam Curie and Mendeleev had been arguing about.
Can elements change?
Before, Li Dong had watched them argue purely for entertainment, hoping to snag a red packet or two if they dropped.
But now, with Qi Yu’s mention of an "atomic fingerprint"...
...Li Dong suddenly realized something.
The two of them probably weren’t arguing about the surface-level question of "Can elements change?" at all.
What they were *really* arguing about was...
...what is the fundamental nature of an element? What defines it, and what determines if it can become another element?
And the modern answer to that question was precisely what Qi Yu had just sketched on the napkin.
An atom’s identity is confirmed by its unique X-ray absorption edge.
This was what Henry Moseley had established in 1913 using X-ray spectroscopy.
Moseley’s Law, for the first time, provided the periodic table with a solid, physical foundation based on experimental data: the atomic number.
The problem was...
Mendeleev died in 1907.
According to the historical timeline, he couldn’t possibly have known about X-ray absorption edges.
And yet, the Mendeleev in the group chat had casually thrown out a term or two...
The more Li Dong thought about it, the more something felt off.
He lifted his teacup for a sip, his expression unchanging, but his mind was already racing.
’Looks like I was wrong before. I thought if I just chewed through this stuff, I could get some red packets from those two big shots.’
’Now it seems it’s not that they don’t know these things. What they need is experimental data—just like Mendel.’

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