Adding an electron would require creating a whole new shell, which takes energy instead of releasing it. They already have a complete valence shell, so there is no room in their orbitals for another electron. However, electron affinity is actually negative for the noble gasses. It is F = k Q 1 Q 2 r 2 Įlectron affinity is the energy released when an electron is added to an atom, producing a negative ion.Įlectron affinity is highest in the upper left, lowest on the bottom right. Lower shells experience this effect more because they are smaller and allow the electrons to interact more.Ĭoulomb's law is an equation that determines the amount of force with which two charged particles attract or repel each other. This effect is mostly canceled out due to the strong attraction to the nucleus, but it does cause electrons in the same shell to spread out a little bit. When two electrons are in the same shell, they will repel each other slightly. Essentially, the core electrons shield the valence electrons from the positive charge of the nucleus.Įlectron-Electron Repulsions The more electron shells there are (a new shell for each row in the periodic table), the greater the shielding effect is. The core electrons repel the valence electrons to some degree. The shielding (or screening) effect is similar to effective nuclear charge. The nucleus attracts the electron, but other electrons in lower shells repel it (opposites attract, likes repel). It is the number of protons in the nucleus minus the number of electrons in between the nucleus and the electron in question. The effective nuclear charge is the amount of positive charge acting on an electron. You must understand them before learning the trends.Įffective Nuclear Charge There are certain phenomena that cause the periodic trends to occur. Organization of Subshells Causes for Trends Potassium has many core electrons the lone outer electron can easily be peeled off due to the "shielding" effect. Elements in the same Group or Family have the same configuration of valence electrons, making them behave in chemically similar ways. The f-block, on the bottom, contains rarer metals including uranium. The d-block, which is the largest, consists of transition metals such as copper, iron, and gold. The s and p blocks make up the main-group elements, also known as representative elements. The halogens, directly to the left of the noble gases, readily gain electrons and react with metals. The noble gases, in the column on the right, almost never react, since they have eight valence electrons, which makes it very stable. The p-block, on the right, contains common non-metals such as chlorine and helium. These elements are the s-block of the periodic table. These elements lose electrons to form bonds easily, and are thus very reactive. The Alkali metals and Alkaline earth metals have one and two valence electrons (electrons in the outer shell) respectively. This is because the elements are listed in part by their electron configuration. The word periodic means that in each row, or period, there is a pattern of characteristics in the elements. The Periodic Table does more than just list the elements.
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