1.2There are only 12 different notes

Ignore octaves for a moment.

The chromatic sequence is:

C – C♯ – D – D♯ – E – F – F♯ – G – G♯ – A – A♯ – B – C

Or using flats:

C – D♭ – D – E♭ – E – F – G♭ – G – A♭ – A – B♭ – B – C

That is the entire pitch universe of ordinary Western equal-tempered piano music before the pattern repeats.

On the piano:

• moving to the immediately adjacent key = one semitone
• two adjacent-key steps = one whole tone

In Russian terminology:

полутон and тон.