Atomic Orbitals PDF

Atomic orbitals Energy levels and sub-levels According to the Bohr model of the atom, electrons exist in energy levels, or principal energy levels The principal energy levels are assigned numbers (n, the principal quantum number), with n = 1 being closest to the nucleus and of lowest en...

Atomic orbitals Energy levels and sub-levels According to the Bohr model of the atom, electrons exist in energy levels, or principal energy levels The principal energy levels are assigned numbers (n, the principal quantum number), with n = 1 being closest to the nucleus and of lowest energy. The further the energy level is from the nucleus, the higher its number (n) and the higher its energy The principal energy levels in the atom (n = 1 to n = 6). The green dot at the center represents the nucleus.  The main energy levels are split into sub-levels, which are assigned a number and the letter s, p, d or f. The number refers to the main energy level and the letter refers to the atomic orbital.  s atomic orbitals are spherical and p atomic orbitals are described as being dumbbell-shaped.  An atomic orbital can hold a maximum of two electrons, according to the Pauli exclusi on principle. There are n number of sub-levels per main energy level, with the number of electrons per main energy level equal to 2n2  Pauli exclusion principle The Pauli exclusion principle states that two electrons cannot have the same quantum number. two electrons can only occupy the same atomic orbital if they have opposite spins. The opposite spins of the electrons are shown by arrows, one pointing up and the other down Heisenberg's uncertainty principle Heisenberg's uncertainty principle states that it is not possible to know, at the same time, the exact position and momentum of an electron we can only state the probability that an electron will be somewhere in a given region of space. The Aufbau principle The overall picture of the atom so far is of main energy levels (n = 1, 2, 3 etc) which are split into sub-levels. Electrons fill these sub-levels according to the Aufbau principle According to the Aufbau principle, electrons fill atomic orbitals of lowest energy first.  The 1s sub-level has the lowest energy, therefore, it is filled first. Within a given main energy level, s orbitals are of lower energy than p orbitals and fill first. The atomic orbitals within a sub-level are of equal energy (known as degenerate orbitals). This includes the three p orbitals in the 2p, 3p and 4p sub-levels and the five d orbitals in the 3d sub- level. There is an overlap between the 3d and 4s sub-levels. This means that the 4s sub-level is of lower energy and fills before the 3d sub-level.  The order of filling of the atomic orbitals Source: byjus.com Electron configurations Electron configurations show how the electrons are arranged in an atom. The number in front of the letter is the principal quantum number, n, which gives the number of the main energy level. The letter refers to the sub-level (s, p, d, f) and the number in superscript gives the number of electrons in the sub-level.  Electron configuration of the first ten elements of the periodic table Condensed electron configurations Condensed electron configurations are a shorthand version of writing the electron configurations for atoms or ions. For example, the electron configuration of bromine (Z = 35) is: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p5 or 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5 Instead of writing the full electron configuration, we can use the notation [Noble gas] to represent part of it. [Ar] 3d10 4s2 4p5 or [Ar] 4s2 3d10 4p5 Worked examples State the electron configuration of a vanadium atom (Z = 23) and the vanadium(II) ion (V2+).  State the electron configuration of a vanadium atom (Z = 23) and the vanadium(II) ion (V2+). The atomic number of vanadium is 23, so it has 23 protons in the nucleus. It is an atom (recall that atoms are electrically neutral because they have the same number of protons and electrons), therefore we can deduce it has 23 electrons. 1s2 2s2 2p6 3s2 3p6 4s2 3d3 or 1s2 2s2 2p6 3s2 3p6 3d3 4s2 Next, the electron configuration of the vanadium(II) ion (V2+) 1s2 2s2 2p6 3s2 3p6 3d3 Exceptions to the Aufbau principle There are two important exceptions to the Aufbau principle. chromium (Cr) and copper (Cu) we would predict the electron configurations to be 1s2 2s2 2p6 3s2 3p6 4s2 3d4 for chromium and 1s2 2s2 2p6 3s2 3p6 4s2 3d9 for copper Chromium: 1s2 2s2 2p6 3s2 3p6 4s1 3d5 or 1s2 2s2 2p6 3s2 3p6 3d5 4s1 Copper: 1s2 2s2 2p6 3s2 3p6 4s1 3d10 or 1s2 2s2 2p6 3s2 3p6 3d10 4s1 Electron configurations of ions Negative ions are formed when atoms gain electrons and positive ions are formed when atoms lose electrons. For example, the electron configuration of the calcium atom (Z = 20) is: 1s2 2s2 2p6 3s2 3p6 4s2 The calcium atom can lose two electrons to form an ion with a two positive charge (Ca2+). 1s2 2s2 2p6 3s2 3p6  The electron configuration of the sulfur atom is: 1s2 2s2 2p6 3s2 3p4 The sulfur atom gains two electrons to form a two negative ion (S 2-)  The electron configuration of the sulfur atom is: 1s2 2s2 2p6 3s2 3p4 The sulfur atom gains two electrons to form a two negative ion (S 2-) 1s2 2s2 2p6 3s2 3p6 Orbital diagrams Orbital diagrams or electron in box diagrams are used to represent electrons in atomic orbitals. Note that the arrows point in opposite directions to represent the opposite spins of the electrons. The electron in box diagrams for carbon, nitrogen and oxygen