A semitone (or half step) is the distance in pitch between a note and its nearest neighbour on a piano keyboard.
Have a look at this keyboard:
Can you see how each of the notes has another note right next to it?
So, the distance or interval between C and C sharp/D flat is a semitone (or half step).
The distance between the A and A flat/G sharp is clearly a semitone/half step.
The interval between two black and white notes that are next to each other on a piano is always a semitone – this is easy to remember.
However, on 2 occasions in the octave there is a semitone interval between 2 white notes.
This occurs between B and C and also between E and F:
The Chromatic Scale
If you count up all the notes then you will find that there are 12 semitones in an octave.
If you play a scale of all 12 semitones in the octave then this is called a chromatic scale.
Here is an example of a chromatic scale played on the piano:
Note: The chromatic scale does not have to begin and end on C. You can begin and end the chromatic scale on any note as long as you play all 12 semitones in the octave.
You can also see from the sheet music above that the chromatic scale can be written using sharps or flats.
This is because notes can sound the same, but have different names.
For example, F sharp sounds the same pitch as G flat.
When two notes have different names, but sound the same pitch then this is called an enharmonic equivalent.
Similarly, the interval between A and B is a tone (the note A sharp/B flat is between the 2 notes):
Remember, the distance between 2 white notes on a piano is not always a tone (whole step).
For example, E does not have a black note between it and F and so a tone up from E is actual F sharp/G flat and a tone down from F is E flat/D sharp.
Also, B and C do not have a black note between them and so a tone up from B is C sharp/D flat, whilst a tone down from C is B flat/A sharp.
The Whole Tone Scale
The above sheet music and audio shows the 2 whole tone scales that are formed by starting on alternate notes of the chromatic scale.
If you start on C and play a whole tone scale you will play the scale on the top line of music.
If you start on the next semitone up (D flat) then you will play the scale on the second line of music.
It doesn’t matter which note of the respective whole tone scales you start on. You can start on any note of the respective scales and you will always end up playing the same notes.