1) I don't generally have problems with hybridization but when I happened to look at https://www.physicsforums.com/showthread.php?t=282170 I saw something that confused me. Poopcaboose said: "Hybrid orbitals work only when bonds are made, they only require the s and p orbitals since the d orbitals are inside of both. The sp3 hybrid orbital means there s orbital has combined with one of the p orbitals to create 3 sp orbitals and one p orbital. This makes way for three sigma bonds and a pi bond". 1a) Isn't the first part incorrect- there are hybrid orbitals that use the D orbital? Not in carbon's case (the subject of the linked topic), but there are instances I believe. 1b) Doesn't sp3 mean that there is 1 S orbital combining with 3 P orbitals to form 4 identical sp3s? This is good for 4 sigma bonds, I believe what he is describing is sp2, right? 2) My elementary understanding of effective nuclear charge says that it remains more or less the same when going down a group. However, when I look at WebElement's website they are using the Clementi-Raimondi method of calculating effective nuclear charge and it appears that it increases, contrary to most Chemistry 101 sites/my textbook. Why is this? With this being so how is the atomic radii trend explained? I suppose that the increase in effective nuclear charge - decreasing the size- is outweighed by the extra energy level's size addition. Thanks for advance, this is greatly confusing me as I look over some stuff in prep. for Chem. 102.