The semitone and tone are the terms used to describe the measurement of the interval between two notes. For example, C to C# is a semitone, while the interval, C to D, is a tone. C first moves to C# then moves over to the note D. C to C# is the first semitone, while C# to D is the second semitone. Two semitones, are equal to one tone, therefore, the interval C to D has a measurement of two semitones or 1 tone. (semitone + semitone = tone). Spend time on the piano. Mark off the tone and semitone intervals in other keys. While in our discussion we will refer to the tone and semitone only, there are many other terms to measure intervals that are way smaller than the semitone. An example is the microtone which is smaller than the semitone.

The tonal structure of major and minor scales is best understood by learning the chromatic scale. There are rules to follow when writing the chromatic scale. In our example we are going to keep it simple at first. You can refer to a more comprehensive account of the chromatic scale in our online tutorials.
An important feature of the chromatic scale is the fact that the distance between adjacent notes is always an interval of a minor second. The minor second interval on the piano will be played from a white key then moving to the adjacent black key. In other words, it has an interval of a semitone. Example, C to Db is a semitone interval.
Notes such as B to C, and E to F, are already semitone intervals and do not have a black key in between.

There are special instances where two white notes on the piano, will form an interval of a semitone or minor second. The two examples are E to F and B to C. You will also note that the black key does not feature between E to F and B to C. As mentioned earlier, E# is enharmonic of F natural and Fb is the enharmonic of E natural.
B# is the enharmonic of C natural and Cb is the enharmonic of B natural.

The major scale has five tones and two semitones. The intervals in all diatonic major scales are specifically arranged as follows: Tone, Tone, Semitone, Tone, Tone, Tone, Semitone. Take a look at the illustration below. Notice that the diatonic scale has only 7 unique notes and the the chromatic scale has 12 unique notes.

Although the notes are different, the tonal structure of the G major scale, remains the same as any other major scale; Tone, tone, semitone, tone, tone, tone and semitone. The seventh note becomes F#, to keep the semitone interval between the seventh and eight notes.
The entry in the chart of scales will read: ' G has 1# - F#

The scale of F major is illustrated below. Notice that the note, B natural, has become Bb (B flat). This, again, has to be done for the tonal structure to match that of the major scale. The entry in the chart of scales will read: ' F has 1b - Bb'

Generally, we do not use accidentals with notes that are included in the key signature. For example, in the key of G, the seventh note is F# (F sharp). The note, F# is included in the key signature. This means that we will not use an accidental with the note F. The note is played as F# due to its inclusion in the key signature.

The discussion above has shown us that we find the key signature from the accidentals used in the scale. The scale of F major had one flat, which is Bb. The scale of G major has one sharp which is, F#. It is good practice to write scales by hand, with key signatures, and without the key signature, using accidentals.

This is a summary of scales that have flats.

The interval of a perfect fifth and a perfect fourth