Worksheet 2: ELECTRONIC STRUCTURE OF THE ATOM Name 1. The number and arrangement of electrons in the energy levels of the atom determine what type of compounds the element will form. To determine the number of electrons in an atom, we consult the periodic chart of the elements in your text book. The chart lists the atomic number, symbol, and atomic weight of each element. The element potassium, for example, is listed as follows. The atomic number represents the number of protons in the atom. (It is not necessary to discuss the atomic weight at this time.) Use the periodic chart to find the name and symbol for the following elements. 6 12.0 a. b. 50 118.7 a. b. 2. Use the periodic chart to find the atomic numbers of the following elements. Iron Gold Fe Au 55.8 a 196.97 a 3. The atomic number tells how many are present in the atom. 4. If an element has an atomic number of 79, there are protons in an atom of that element.
5. The atomic number represents the number of protons in an atom, which is also the number of electrons since there are an equal number of protons and electrons in every atom. Element Atomic Number Number of Protons Number of Electrons Ne 10 10 10 Fill in the needed information below. Element Atomic Number Number of Protons Number of Electrons Cl Sc Cr Pb U 6. The next task is to determine how many electrons go into each of the seven energy levels. We can do this by using the mathematical formula 2n2, where n is the number of the energy level. Energy Level = n Substituted for n in Formula Maximum Number of Electrons in Level 1 2n 2 2 (1 x 1) = 2 2 2n 2 2 (2 x 2) = 8 3 5 6 7 7. To arrange the electrons in the energy levels, we use our ability to find the total number of electrons an atom has and our ability to find the maximum number of electrons in each energy level. Except for a limitation that will be explained later, the energy levels fill from the first one on out. The first level of any atom can hold maximum of two electrons and the second level can hold a maximum of eight. Element Number of Electrons Arrangement of Electrons in Energy Levels 1 2 3 4 F 9 2 7 The fluorine atom has a total of nine electrons to distribute in the seven levels. The first level took two of the nine electrons, leaving only seven for the second level even though it could hold eight.
Complete the following. Element a) S b) P c) Mg d) Ca Number of Electrons Arrangement of Electrons in Energy Levels 1 2 3 4 8. All atoms are neutral. This means that there is always an equal number of positive and negative charges in an atom. Because protons are positively charged and electrons are negatively charged, there must therefore be an equal number of electrons and protons in an atom. An element with 29 electrons per atom must also have protons per atom. What element is this? 9. Ions on the other hand have an imbalance of protons and electrons. This means that there are always an unequal number of electrons to protons. The proton amount is fix however, based on the identity of the element, therefore the number of electrons must vary in order to account for charge of the atom (ion). If a chloride anion has a charge of 1, then the number of proton is fix at 17 (the atomic number or the number of protons). The number of electrons therefore must be 18. The 17 positive proton and the 18 negative electrons adds up to 1 net charge. Write out the electron and protons each of the ions (or atom) below posses. ion or atom No. of p + / e - 3Li + 15P -3 14Si 21Sc +3 32Ge -4 34Se -1 10. The electron configuration of an atom is the nomenclature illustrating how electrons are distributed among the various atomic orbitals. The atom hydrogen has one electron found in the 1s orbital. H has the electron configuration 1s 1. atom carbon has the electron configuration C = 1s 2 2s 2 2p 2, or it can also be written C = [He]2s 2 2p 2 where [He] represents the electron configuration 1s 2. Complete the electron configuration for the following atoms. The filling sequence is 1s-2s-2p-3s-3p-4s-3d-4p-5s-4d-5p-6s-4f-5d-6p Atom electron-configuration Atom electron-configuration i.e. Kr 1s 2 2s 2 2p 6 3s 2 3p 6 4s2 3d 10 4p 6 He The P Ar Ca Mg Li Ge
11. The electron configuration of an ion is determine in the same manner as that for an atom except that the number of electron must be adjusted based on the charge of the ion. An atom with the same number of electron as an ion will have the same electron configuration. From the above example, the carbon atom has six electrons and has an electron configuration of C = [He]2s 2 2p 2. A nitrogen +1 cation will also have the exact electron configuration N + = [He]2s 2 2p 2. Note that the nitrogen atom has an electron configuration of N = [He]2s 2 2p 3 but the +1 ion has one less electron, 6 instead of 7. Similarly, O +2, F +3, B -1 all have six electrons and therefore all have the electron configuration, [He]2s 2 2p 2. Complete the electron configuration for the following atoms. Atom electron-configuration Atom electron-configuration i.e. 32Ge -4 1s 2 2s 2 2p 6 3s 2 3p 6 4s2 3d 10 4p 6 34Se -1 15P -3 21Sc +3 20Ca +2 15N -3 10. Orbital box diagrams are used to show the location of electrons in the outer shell. Inner ( core ) electrons are those that correspond to the nearest noble gas and are not typically represented. So iron, which has an electron configuration of [Ar] 4s 2 3d 6 would have an orbital box diagram that looks like 4s 3d The presence of unpaired electrons will cause the species to be paramagnetic; if ALL the electrons are paired it is said to be diamagnetic. Write out the electron configurations for the following atoms and ions. Determine the number of unpaired electrons in the ground state. (continue on back if needed) 22Ti +3 25Mn +2 15P 65Tb +4 78Pt +2
11. List all elements beginning with the letter "R" (with Z < 88) which are diamagnetic and write their electron configuration. 12. Assign all possible values for the quantum numbers n, l, ml for the following orbitals (assume that there is no specific spatial assignment based on the ml value): 2pz 3dz2 3fxyz 4s