What is the atomic number of a neutral atom with an electron configuration of 1s22s22p63s23p54s24p1?

Atomic number is 21. Element is Scandium. Due to typesetting issues, I will assume that each digit following a letter is actually a superscript. So adding spaces to your electron configuration we get 1s2 2s2 2p6 3s2 3p5 4s2 4p1 The 1st number and the letter designate the electron shell being named. The 2nd number is the number of electrons in that shell. So 1s2 means that there's 2 electrons in the 1s shell. So let's count the total number of electrons in this configuration. 1s2 - 2 electrons in the 1s shell 2s2 - 2 electrons in the 2s shell 2p6 - 6 electrons in the 2p shell 3s2 - 2 electrons in the 3s shell 3p5 - 5 electrons in the 3p shell 4s2 - 2 electrons in the 4s shell 4p1 - 2 electrons in the 4p shell For a total of 2+2+6+2+5+2+2 = 21 electrons. Since the atom has a neutral charge, that means that there's 21 protons in the atom and it's atomic number is 21. Looking at the periodic table, element number 21 is Scandium. Abbreviation is Sc.