For the second period ( n=2) there is a p block but no d block in the usual 'long form' of the periodic table it is customary to leave a gap between these two blocks in order to accommodate the d blocks that occur at n=3 and above. For n=1 there is no p block, and the s block is split so that helium is placed in the same group as the other inert gases, which it resembles chemically. The 'block' nomenclature shown above refers to the sub-orbital type (quantum number l, or s-p-d-f classification) of the highest-energy orbitals that are occupied in a given element. The first period is split in order to place H above Li and He above Ne. Thus the first short-period elements H and He are chemically similar to the elements Li and Ne at the beginning and end of the second period. The rows are aligned in such a way that the elements in each vertical column possess certain similarities. Periods: To construct the table, we place each sequence in a separate row, which we call a period. H He | Li Be B C N O F Ne | Na Mg Al Si P S Cl Ar | Ca. For the elements listed above, these breaks can be indicated by the vertical bars shown here in color: Now if we look at the various physical and chemical properties of these elements, we would find that their values tend to increase or decrease with Z in a manner that reveals a repeating pattern- that is, a periodicity. H He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K Ca. To understand how the periodic table is organized, imagine that we write down a long horizontal list of the elements in order of their increasing atomic number.

Our goal in this lesson is to help you understand how the shape and organization of the modern periodic table are direct consequences of the atomic electronic structure of the elements. At that time, nothing was known about atoms the development of the table was entirely empirical. The periodic table in the form originally published by Dmitri Mendeleev in 1869 was an attempt to list the chemical elements in order of their atomic weights, while breaking the list into rows in such a way that elements having similar physical and chemical properies would be placed in each column.

State the meaning and significance of electronegativity.

Define ionization energy and electron affinity, and explain the periodic general trends.

Comment on the concept of the 'size' of an atom, and give examples of how radii are defined in at least two classes of of substances.For the first eighteen elements, you should be able to predict the formulas of typical binary compounds they can be expected to form with hydrogen and with oxygen.You should be able to sketch out the general form of the periodic table and identify the various blocks and identify the groups corresponding to the alkali metals, the transition elements, the halogens, and the noble gases.Make sure you thoroughly understand the following essential ideas:

Effective nuclear charge periodic trend