ElectronconfigurationsElectronic configurationsrepresent the electronic structures of atomsEVIDENCEFORTHE ELECTRONIC STRUCTURE ORATOMSAmeasure of how well an atom can hold its electrons is given bythe ionisation energy. This is the energy change when a mole ofelectrons is removed from a mole of particles in the gas phasee.g. X(g) → X(g) + e- △E= ionisation energy16
16 Electron configurations Electronic configurations represent the electronic structures of atoms A measure of how well an atom can hold its electrons is given by the ionisation energy. This is the energy change when a mole of electrons is removed from a mole of particles in the gas phase. EVIDENCE FOR THE ELECTRONIC STRUCTURE OF ATOMS e.g. X(g) → X+ (g) + e- △E= ionisation energy
Electronconfigurationslog10AHn61st shell5-1s22nd shell42s22p63rd shell33s23p6“4thshell24s1Successiveionization energies1026841012141618ionisationnumberSuccessive electrons can be stripped offan atom one after theother until only the nucleus is left. If these successive ionizationenergies are plotted (usually on a log scale because the valuesget so big) against the number of electrons removed, a graph isproduced which clearly shows the shell structure of the atom.The graph to the right shows this for potassium17
17 Electron configurations Successive electrons can be stripped off an atom one after the other until only the nucleus is left. If these successive ionization energies are plotted (usually on a log scale because the values get so big) against the number of electrons removed, a graph is produced which clearly shows the shell structure of the atom. The graph to the right shows this for potassium. Successive ionization energies
Electron configurations2nd3rd1stshellshellshellHedecreasesdownagroupNeincreasesacrossaperiodArcompletelyfillingeachcporbitalhalfBefillingMgelectron-electronSieachUFirst ionization energiesrepulsiondecreasesPorbitalAINafillinganattractionchangefromsorbitalstoporbitalatomicnumberIf the first ionization energies for each element are plottedagainst atomic number, then once again the shell structureis revealed, but this time in a different way.18
18 Electron configurations If the first ionization energies for each element are plotted against atomic number, then once again the shell structure is revealed, but this time in a different way. First ionization energies
Electron configurationsRULES FOR WORKING OUTTHE ELECTRONICSTRUCTURE OFATOMS1. Fill up the orbitals starting with those of lowest energy (nearestthe nucleus) and working outwards. This building up process issometimes given the German name the aufbau principle (构造).The pattern on theleft will helpyou remember the order.An atom whose electrons are in the orbitals of lowest availableenergy is in its ground state. Most atoms are in their ground stateat room temperature.2. Each orbital can have a maximum of two electrons in it (this isknown as the Pauli principle).3. When you are filling a sub-shell, half fill each orbital beforecompletely filling any one (known as the Hund principle)19
19 Electron configurations 1. Fill up the orbitals starting with those of lowest energy (nearest the nucleus) and working outwards. This building up process is sometimes given the German name the aufbau principle (构造）. The pattern on the left will help you remember the order. An atom whose electrons are in the orbitals of lowest available energy is in its ground state. Most atoms are in their ground state at room temperature. 2. Each orbital can have a maximum of two electrons in it (this is known as the Pauli principle). 3. When you are filling a sub-shell, half fill each orbital before completely filling any one (known as the Hund principle). RULES FOR WORKING OUT THE ELECTRONIC STRUCTURE OF ATOMS