Part II: Diatonic Materials, Units 1-3
Study Guide 2: The Tonic and Dominant Triads; Passing Tones and Auxiliary Tones
Keyboard and choral voicing
A triad is in root position if the root is in the bass. In these initial exercises, the root should be doubled, in order to create four voices. In keyboard voicing, three voices are in the right hand part. The bass alone is in the lower part:

In choral voicing, soprano and alto voices are written on the upper staff; tenor and bass are on the lower staff. The stem direction should be upward for the higher voice and downward for the lower voice The spacing between notes in chords can be close or open. In close spacing, the three upper parts are as close together as possible. In open spacing, a tone of the same triad can be placed between each adjacent pair of upper voices. Both kinds of voicing are employed here:

Connection of Tonic and Dominant Triads in Root Position
It is generally best to double the root in both tonic and dominant triads. The third of the dominant chord, the leading tone, should never be doubled. In the minor mode, the leading tone must be raised. The accidental that affects the leading tone is shown next to the Roman numeral V in the analysis. In maintaining a common-tone connection between the tonic and dominant chords:
- The bass takes the root of the second chord.
- The common tone is maintained in the same voice.
- The remaining two voices move by conjunct (stepwise) motion to the nearest notes of the second chord.
- In connection of V to I, the leading tone normally resolves to the tonic note.

Some melodic motions, including scale degree 2 to 1, require a noncommon-tone connection:
- The upper three voices normally move contrary to the bass to the nearest notes of the second chord.
- In connecting V to I, the leading tone, a tendency tone, does not resolve to the tonic, but skips down to the dominant. This is known as free resolution of the leading tone. This can occur only when the leading tone is in an inner voice.
Free resolution of the leading tone is illustrated below. Note that the third of the dominant triad, the leading tone, has been raised as required for a minor key:

See the video: Harmonizing a Melody
Nonharmonic Tones: Passing and Auxilliary Tones
Any note that is not heard as a member of the prevailing harmony is defined as a nonharmonic (nonchord) tone. The following are two types of nonharmonic tones; other types will be introduced in subsequent units. The passing tone fills in the gap between two chord tones:

The auxiliary (neighbor) tone is used between a chord tone and its repetition:

In this opera aria, the singer is accompanied with an orchestral setting of tonic and dominant triads. Notice the upper and lower auxiliary tones in the first full measure:

Passing and auxiliary tones are also prominent in this excerpt for piano:

For definitions of all types of nonharmonic tones, see Part V, Unit 3 in the textbook. Appogiaturas and Suspensions are covered in Study Guide 5.
For more on voice leading in strict four-part writing, with definitions and a summary of procedures, refer to Part V, Units 4 and 5 in the textbook.
Audio credits
Mozart, The Magic Flute. Musopen (public domain)