Ignoring, for the moment, electron spin and electron-electron interaction, suppose that one electron in a helium atom is in the ground hydrogen-like state (0,0,0) and the other is in an excited state (un, l, (i) explain why w(r1, r2) = w0,0,0(r1)& n,1,mų (r2) is not a suitable wave function to describe the helium atom in this state. (ii) explain how this problem is overcome? (b) assume now that spin and electron-electron interaction are taken into account. all states of the atom can be classified as singlet states or triplet states. answer the following questions: (i) give a brief explanation of what distinguishes a singlet state from a triplet state. (ii) the singlet and triplet states of the same electron configuration have different energies. explain why. (iii) draw a schematic diagram showing the states for a helium atom for an electron configuration 1s2p, taking account of electron-electron interaction, exchange energy and spin-orbit coupling effects. spacings do not need to be to scale, but you should label the levels with relevant quantum numbers and spectroscopic notation. (iv) for the ground state electron configuration 1s”, explain why there is a singlet state only.

Up of elements with the same number of valence electrons. vertical column in the periodic table of elements such as alkali metals or halogens. a horizontal row of elements in the periodic table. this is a characteristic of the elements in the periodic table that shows a pattern. it may increase or decrease across or down the table. periodic trend these are the highly reactive elements located in group 1 of the periodic table. these elements have one electron in their outer energy level which makes them highly reactive with water and halogens. these are the reactive elements located in group 2 of the periodic table. these elements have two electrons in their outer energy level which makes them reactive with water and halogens. alkaline earth metals these are the group 3 or d-block elements. these dense metals with high boiling points can have different oxidation states and all are solid at room temperature with the exception of mercury. transition metals this is the highly reactive family of elements with 7 valence electrons. this is an element with full valence shell, very unreactive. this is a group of elements with few valence electrons that conducts heat and electricity. one of a class of elements having properties intermediate to metals and nonmetals. this is a type of element that has many valence electrons, not a conductor.