"Where are the electrons?"
Kana gazed at a molecular model.
Rei smiled. "Everywhere and nowhere."
"Huh?"
Milia explained. "Electrons are both particles and waves."
"Waves?"
"Think of them as probability distributions called electron clouds," Rei drew a diagram in the notebook.
Kana peered in. "Cloud?"
"Places where electrons have high probability of existing."
Milia added. "Called orbitals. s orbital, p orbital, d orbital..."
"Different shapes?"
"s orbitals are spherical. p orbitals are dumbbell-shaped," Rei showed a model.
Kana touched it. "Does this shape have meaning?"
"Determines bond direction."
Milia continued. "Consider water molecule H₂O. Oxygen's p orbital bonds with hydrogen."
"How?"
Rei explained. "Share electrons. Covalent bond."
"Share?"
"Two atoms jointly possess an electron pair."
Kana wrote in her notebook. "Electrons between two atoms?"
"Yes. A molecular orbital forms."
Milia drew a diagram. "Atomic orbitals overlap to create bonding orbitals."
"Overlap?"
"When waves overlap, places strengthen and places weaken," Rei explained.
"Constructive and destructive interference."
Kana tried to understand. "When they strengthen?"
"Bonding orbital. Energy decreases. Stable."
"When they weaken?"
"Antibonding orbital. Energy increases. Unstable."
Milia added. "Electrons enter bonding orbitals. So bonds form."
Kana asked. "So what about double bonds?"
"σ bond and π bond," Rei answered.
"σ? π?"
"σ bonds overlap head-on. Strong."
Milia continued. "π bonds overlap sideways. Weak."
"But together they make a strong bond."
Kana looked at the model. "Oxygen molecule O₂?"
"Double bond. One σ and one π," Rei explained.
"Nitrogen N₂?"
"Triple bond. One σ and two π. So very stable."
Milia added. "That's why atmospheric nitrogen is unreactive."
Kana admired. "Properties change with number of bonds."
"Yes. Bond energies differ too."
Rei showed numbers. "C-C single bond is about 350 kJ/mol. C=C double bond is about 600 kJ/mol."
"Not double?" Kana noticed.
"π bonds are weaker than σ bonds."
Milia gave another example. "For carbon, hybrid orbitals are important."
"Hybrid?"
"s and p orbitals mix to create new orbitals."
Rei drew a diagram. "sp³ hybridization gives tetrahedral. Methane CH₄."
"sp² hybridization gives trigonal planar. Ethylene C₂H₄."
"sp hybridization gives linear. Acetylene C₂H₂."
Kana organized. "Hybridization determines shape?"
"Yes. Molecular geometric structure."
Milia continued. "Peptide bonds in proteins are also planar because of this."
"Because of sp² hybridization."
Rei nodded. "Chemistry is determined by electron configuration."
Kana lifted an electron model. "These tiny particles determine everything."
"Not particles, waves," Milia corrected.
"Both wave and particle," Rei smiled.
"The mystery of quantum mechanics."
Kana asked. "Where's the electron cloud boundary?"
"Depends on definition," Rei answered.
"Like the range where 90% probability exists."
Milia added. "But actually it extends infinitely."
"Infinite?" Kana was surprised.
"Probability never becomes zero. Just becomes very small."
Rei said quietly. "So all electrons extend throughout the universe."
"But most stay near atoms."
Kana looked out the window. "My electrons reach the stars too?"
"Theoretically," Milia smiled.
"But perceptible effects are only nearby."
Rei closed the notebook. "Beyond electron cloud boundaries, the universe is connected."
Kana was moved. "Chemistry becomes philosophy too."
"Quantum mechanics betrays intuition."
Milia put away the model. "But that's nature's truth."
The three quietly left the lab.
Kana murmured. "I wonder if my electron cloud connects with someone."
Rei and Milia laughed.
"Of course. Everything is connected."
Electrons, as invisible waves, fill the world.