This helps clarify the families: https://en.wikipedia.org/wiki/STM32
"The STM32 F3-series is the second group of STM32 microcontrollers based on the ARM Cortex-M4F core. The F3 is almost pin-to-pin compatible with the STM32 F1-series. ...
"The STM32 F2-series of STM32 microcontrollers based on the ARM Cortex-M3 core. It is the most recent and fastest Cortex-M3 series. The F2 is pin-to-pin compatible with the STM32 F4-series ...."
