This is a question regarding Chatzi Kaddish and Kaddish shalem
a) If the Chatzi kaddish serves as a separation between the 7 regular aliyot and the maftir, why is it recited on monday and Thursday mornings after the Torah reading if there is no maftir (as is the practice on shabbat afternoon when there is no maftir and the kaddish is not recited after the Torah reading)
b) Why do we say a Kaddish shalem after the Shemona Esrei and before the Torah reading on days we say Musaf, whereas if there was no musaf there would be a chatzi kaddish after the Shemona Esrei and and before the Torah reading? (What is it about Musaf that changes that kaddish from a chatzi kaddish to a kaddish Shalem?)
Please include sources.
a) The idea of having Kaddish between the seven regular aliyot and Maftir is meant to show the distinction between the main obligation and the added aliyah, which does not count towards the requirement of seven aliyos (see Tosafot, Megilla 23a). However, this is not the actual reason for the Kaddish, and only the reason it was it is placed in between the two.
The actual reason for the Kaddish is to separate between the different units of davening (Pri Megadim, Orach Chayim, Mishbetzot Zahav 55:1), of which Keriyas Ha-Torah is one. On Shabbos Mincha we also say Kaddish after the reading of the Torah, and this is the Kaddish that is recited before Shemoneh Esrei (Mishnah Berurah 292:4).
b) We say Kaddish Shalem, which includes a petition that our prayers should be answered, after the Shemoneh Esrei prayer. However, where there is no mussaf prayer, we delay it until after the Uva Le-Zion prayer, so that the petition that our prayers are answered will include this prayer. On days when there is mussaf, we say Kaddish Shalem straight after Shemoneh Esrei (the preferred time), because there is a another Kaddish Shalem to cover the Uva Le-Zion prayer (either at mincha or after mussaf).