Atomic orbitals, electronic configurations and the Periodic Table

The three degenerate p orbitals are described as being dumbbell-shaped and are each aligned along one of the three perpendicular axes. For example, the p orbital has a 

The third shell can hold a maximum of 18 electrons. Two of these electrons are in the s orbital and the three p orbitals hold another six electrons. The remaining 10 electrons are accommodated in d orbitals. As an orbital can hold a maximum of two electrons, there must be five d orbitals in the third and subsequent shells. 

You must know the shapes of the s and p orbitals and be able to draw them. You must also remember that the maximum number of electrons in any orbital is two. 

You must be able to recognise the d orbitals from diagrams and realise that the has a different shape from the others. 

These five d orbitals are degenerate with each other, but have higher energies than the s and p orbitals in the same shell. Four of the d orbitals are shaped like a double dumbbell. 

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Inorganic and physical chemistry Atomic orbitals, electronic configurations and the Periodic Table 1... 

ATOMIC ORBITALS, ELECTRONIC CONFIGURATIONS AND THE PERIODIC TABLE 2... 

Electron Spin and the Pauli Exclusion Principle Orbital Energy Levels in Multielectron Atoms Electron Configurations of Multielectron Atoms Electron Configurations and the Periodic Table... 

The energy-ordering scheme (5-58) coupled with the Pauli or exclusion principle and Hund s rule leads us to a simple prescription for building up the electronic configurations of atoms. This aufbau principle is familiar to chemists and leads naturally to a correlation between electronic structure and the periodic table. The procedure is to place all the electrons of the atom into atomic orbitals, two to an orbital, starting at the... 

Plan The atomic number tells us the number of electrons, and the periodic table shows the order for filling sublevels. In the partial orbital diagrams, we include all electrons after those of the previous noble gas except those in filled inner sublevels. The number of inner electrons is the sum of those in the previous noble gas and in filled d and/ sublevels. Solution (a) For K (Z = 19), the full electron configuration is l5 25 2//3 3//4. ... 

Physical and Chemical Properties Sodium is an alkali metal which readily loses one electron hence, + 1 is its only oxidation state. The atomic number of sodium in the Periodic Table of the elements is 11 (Group 1), and its atomic weight is 22.98977. Sodium melts at 97.8°C and boils at 881.4 °C. The sodium atom in its ground state has the electron configuration 1 s, 2 s p , 3 s which corresponds to a case with an electronic nature of the inert gas neon, and an additional single-valence electron in the 3 s orbital. The configuration occurs only in the oxidation state I" in ionic compounds. Most of the ionic compounds are soluble in water and highly ionized. 

The electron configuration or orbital diagram of an atom of an element can be deduced from its position in the periodic table. Beyond that, position in the table can be used to predict (Section 6.8) the relative sizes of atoms and ions (atomic radius, ionic radius) and the relative tendencies of atoms to give up or acquire electrons (ionization energy, electronegativity). 

The reason usually cited for the great similarity in the properties of the lanthanides is that they have similar electronic configurations in the outermost 6s and 5d orbitals. This occurs because, at this point in the periodic table, the added electrons begin to enter 4f orbitals which are fairly deep inside the atom. These orbitals are screened quite well from the outside by outer electrons, so changing the number of 4/electrons has almost no effect on the chemical properties of the atom. The added electrons do not become valence electrons in a chemical sense—neither are they readily shared nor are they readily removed. 

Locate the element in the periodic table, and find the nearest noble gas with smaller atomic number. Start with the configuration of that noble gas, and add enough additional electrons to the next filling orbitals to give the neutral atom. 

The concept of an octet of electrons is one of the foundations of chemical bonding. In fact, C, N, and O, the three elements that occur most frequently in organic and biological molecules, rarely stray from the pattern of octets. Nevertheless, an octet of electrons does not guarantee that an inner atom is in its most stable configuration. In particular, elements that occupy the third and higher rows of the periodic table and have more than four valence electrons may be most stable with more than an octet of electrons. Atoms of these elements have valence d orbitals, which allow them to accommodate more than eight electrons. In the third row, phosphoms, with five valence electrons, can form as many as five bonds. Sulfur, with six valence electrons, can form six bonds, and chlorine, with seven valence electrons, can form as many as seven bonds. 

The block s, on the left of the Table, contains the alkali and alkaline earth metals. Each atom of these metals possesses an inert gas core and one or two electrons in the s orbital of the valence shell, that is, an external electron configuration ns1 or ns2 where n is the value of the principal quantum number, and also the period number in the Periodic Table. Notice however that He, owing to its general chemical inertness and to the behaviour similarity with the other noble gasses is generally placed at the far right of the Table. The p block contains elements corresponding to electron... 

It is possible to distinguish atoms by writing sets of quantum numbers for each of their electrons. However, writing quantum numbers for an atom such as uranium, which has 92 electrons, would be mind-bogglingly tedious. Fortunately, chemists have developed a shortcut to represent the number and orbital arrangements of electrons in each atom. As you will see shortly, these electron configurations, as they are called, are intimately connected to the structure and logic of the periodic table. 

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