By playing on white notes from C to the next C we get a major scale. Some of the steps are tones and some are semitones. The semitones come between E and F and between B and C, i.e. between the 3rd and 4th and between the 7th and 8th note of the scale. All major scales have this pattern (tone, tone, semitone, tone, tone, tone, semitone).