Soon is an adverb; be is a verb.
"Soon" is an adverb as it qualifies a verb, e.g. Soon he will run his race.
Write to you soon as a phrase is not one specific part of speech. Write is a verb. To is a preposition. You is a pronoun (object of the preposition.) Soon is an adverb.
"Deface" is a verb. For example: He plans to deface the wall as soon as he finds the chalk.
The word "imminent" is an adjective. It is used to describe something that is about to happen or occur soon.
The verb 'will' is an auxiliary verb in that example.The main verb is 'go'.
"Shortly" is usually an adverb, used to describe when something will happen soon or briefly.
The part of speech for this particular word is a noun.
part of speech
The part of speech for "answer" is a noun.
adverb
what part of speech is beneath
The part of speech for "unfamiliar" is an adjective.