The basic building block of matter. The way atoms interact each other is a critical part of electrical engineering but isn’t directly applicable until dealing with semiconductor devices.
The smallest particle of an element that possesses the unique characteristics of that element.
Electronic Devices : Conventional Current Version, 9th Edition by Thomas L. Floyd
The smallest particle of an element that still has the same characteristics as the element.
Grob’s Basic Electronics, 11th Edition by Mitchel E. Schultz