![]() ![]() The only safe thing to do is to ignore argon in the discussion which follows. The general trend towards smaller atoms across the period is NOT broken at argon. It isn't fair to compare these with a van der Waals radius, though. It is fair to compare metallic and covalent radii because they are both being measured in tightly bonded circumstances. The van der Waals radius for Ar because it doesn't form any strong bonds. The figures used to construct this diagram are based on: The diagram shows how the atomic radius changes as you go across Period 3. The repulsion between the two electrons in the same orbital means that the electron is easier to remove than it would otherwise be. The difference is that in the sulphur case the electron being removed is one of the 3p x 2 pair. The screening is identical in phosphorus and sulphur (from the inner electrons and, to some extent, from the 3s electrons), and the electron is being removed from an identical orbital. Both of these factors offset the effect of the extra proton.Īs you go from phosphorus to sulphur, something extra must be offsetting the effect of the extra proton The 3p electron is slightly more distant from the nucleus than the 3s, and partially screened by the 3s electrons as well as the inner electrons. Offsetting that is the fact that aluminium's outer electron is in a 3p orbital rather than a 3s. You might expect the aluminium value to be more than the magnesium value because of the extra proton. ![]() That increases ionisation energies still more as you go across the period. In fact the increasing nuclear charge also drags the outer electrons in closer to the nucleus. That causes greater attraction between the nucleus and the electrons and so increases the ionisation energies. The major difference is the increasing number of protons in the nucleus as you go from sodium across to argon. These are all the same sort of distances from the nucleus, and are screened by the same electrons in the first and second levels. In the whole of period 3, the outer electrons are in 3-level orbitals. Use the BACK button on your browser to return to this page. Note: If you aren't certain about the reasons for any of these statements, you must go and read the page about ionisation energies before you go any further. Whether the electron is alone in an orbital or one of a pair. The amount of screening by inner electrons The distance of the outer electron from the nucleus Notice that the general trend is upwards, but this is broken by falls between magnesium and aluminium, and between phosphorus and sulphur. The pattern of first ionisation energies across Period 3 It is the energy needed to carry out this change per mole of X. The first ionisation energy is the energy required to remove the most loosely held electron from one mole of gaseous atoms to produce 1 mole of gaseous ions each with a charge of 1+. Use the BACK button on your browser to return quickly to this page. Note: If you aren't happy about electronic structures, it is essential to follow this link before you go any further. In each case, represents the complete electronic structure of a neon atom. Just as a reminder, the shortened versions of the electronic structures for the eight elements are: Na In Period 3 of the Periodic Table, the 3s and 3p orbitals are filling with electrons. These topics are covered in various places elsewhere on the site and this page simply brings everything together - with links to the original pages if you need more information about particular points. It covers ionisation energy, atomic radius, electronegativity, electrical conductivity, melting point and boiling point. This page describes and explains the trends in atomic and physical properties of the Period 3 elements from sodium to argon. Atomic and physical properties of period 3 elementsĪTOMIC AND PHYSICAL PROPERTIES OF THE PERIOD 3 ELEMENTS ![]()
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