None of those are syllables in Italian. The first three consist of a consonant + a semivowel (glide), and they go at the beginning of a syllable. Note that the L in gl and the N in “gn” are palatalized, that is, your tongue is close to the position for the “i” (similar to hanyu pinyin x, q, j). Exception: Gli is a syllable when followed by a consonant either in the same word or at the beginning of the next word. The sc is a consonant cluster and also goes with the following syllable (other examples of “esse impura” are st and sp) Exception: “sci” is pronounced like English sh only it is longer, and serves to both close the syllable before it and begin the following syllable.