"Beautiful..."
Kana stared at the orbital diagram.
Rei smiled. "s orbital. Spherically symmetric."
"Like flower."
"p orbitals are more complex."
On screen appeared dumbbell-shaped orbitals.
"Three exist. px, py, pz," Milia explained.
"Why three?"
"Because three-dimensional space. Along x, y, z axes."
Kana asked. "What about d orbitals?"
Rei showed a new diagram. "Five. More complex shapes."
"Pretty..."
"f orbitals are seven. Even more complex."
Milia added. "But all expressible by equations."
"Equations?" Kana was surprised.
"Solutions to Schrödinger equation. Wave functions."
Rei explained. "Electron is both particle and wave."
"Wave?"
"Probability wave. Orbital is probability distribution where electron is found."
Kana wrote in her notebook. "Electron is here?"
"Probabilistically. Position isn't determined until observed."
"Strange..."
"Essence of quantum mechanics," Milia said.
Rei continued. "Each orbital is specified by quantum numbers."
"Quantum numbers?"
"n, l, m, s. Four numbers."
"n is principal quantum number. Energy level."
"l is angular momentum quantum number. Orbital shape."
"m is magnetic quantum number. Orbital orientation."
"s is spin quantum number. Electron rotation."
Kana was overwhelmed. "Complex..."
"But regular," Rei said.
Milia drew a diagram. "Electrons fill from inside out."
"1s, 2s, 2p, 3s, 3p..."
"Pauli exclusion principle. Maximum two electrons per orbital."
Rei supplemented. "Can coexist if opposite spin."
Kana asked. "What about chemical bonds?"
"Orbital overlap," Milia answered.
"When two atomic orbitals overlap, bonding orbital forms."
Rei showed a diagram. "σ bond and π bond."
"σ is overlap along axis."
"π is overlap perpendicular to axis."
Kana showed interest. "What about double bonds?"
"One σ and one π."
"Triple bonds?"
"One σ and two π."
Milia explained. "π electrons move easily."
"Why?"
"Because extended orbitals. Especially in conjugated systems."
Rei drew another diagram. "System with alternating double bonds. π electrons delocalize."
"Delocalize?"
"Don't stay at specific bond, spread over whole molecule."
Kana understood. "Electron cloud?"
"Yes. This causes color and conductivity."
Milia gave example. "β-carotene. Long conjugated system, so orange."
"Color and electrons?"
"Absorbs visible light. Electrons get excited."
Rei explained. "Longer conjugated system absorbs lower energy light."
"So color changes."
Kana organized in notebook. "Electron orbitals determine color."
"Most properties determined by electron configuration," Milia said.
Rei continued. "Reactivity, stability, magnetism... all electrons."
Kana murmured. "Fell in love with electron orbitals..."
The two looked at Kana.
"So beautiful, complex, determining everything."
Milia smiled. "Many scientists feel same."
Rei said quietly. "Beauty of invisible things."
Kana stared at diagram. "Does this shape really exist?"
"As probability distribution, exists."
"But invisible."
"Can't see directly even with electron microscope. But can observe indirectly."
Milia added. "Equations and experiments match."
"That's reason to believe."
Kana closed notebook. "Believe in invisible things."
Rei nodded. "Science's faith."
"But faith based on evidence," Milia said.
The three fell silent. Invisible orbitals determine everything.
"Electrons play cosmic music," Kana murmured.
Rei smiled. "Poetic but accurate."
Milia opened window. "Quantum world is poetic world."
Kana took deep breath. "Can I fall in love?"
"Already in love," the two laughed.