Data taken from John Emsley, The Elements , 3rd edition. Oxford: Clarendon Press, The electron affinity of an element is the energy change which accompanies the addition of an electron to an atom in the gas phase to produce a negatively charged anion:. Electron affinities are usually negative values, since energy is usually released an exothermic energy change when an electron is added to a neutral atom.
If the resulting anion is stable, the value for the electron affinity will be negative; the more stable the anion is, the larger the negative number will be. If the resulting anion is unstable, the value for the electron affinity will be positive.
Electron affinity generally increases from bottom to top within a group that is, it goes to larger negative numbers , and increases from left to right within a period. The halogens in Group 7A all have large negative electron affinities, since they are only one electron away from having a noble gas configuration, they easily accept another electron to generate stable halide anions. The noble gases already have a complete set of electrons, and an additional electron must go into the next highest shell, which will cost energy to start populating.
The trends for electron affinity are not as smooth as those for atomic radius , ionization energy , and electronegativity , as can be seen on the following graphs. H Li Be B C O F Ne Na Mg Al Si P S Cl Ar K Ca Sc xx. First electron affinities have negative values. For example, the first electron affinity of chlorine is kJ mol By convention, the negative sign shows a release of energy.
When an electron is added to a metal element, energy is needed to gain that electron endothermic reaction. Metals have a less likely chance to gain electrons because it is easier to lose their valance electrons and form cations. It is easier to lose their valence electrons because metals' nuclei do not have a strong pull on their valence electrons.
Thus, metals are known to have lower electron affinities. This trend of lower electron affinities for metals is described by the Group 1 metals:. When nonmetals gain electrons, the energy change is usually negative because they give off energy to form an anion exothermic process ; thus, the electron affinity will be negative. Nonmetals have a greater electron affinity than metals because of their atomic structures: first, nonmetals have more valence electrons than metals do, thus it is easier for the nonmetals to gain electrons to fulfill a stable octet and secondly, the valence electron shell is closer to the nucleus, thus it is harder to remove an electron and it easier to attract electrons from other elements especially metals.
Thus, nonmetals have a higher electron affinity than metals, meaning they are more likely to gain electrons than atoms with a lower electron affinity.
For example, nonmetals like the elements in the halogens series in Group 17 have a higher electron affinity than the metals. This trend is described as below.
Notice the negative sign for the electron affinity which shows that energy is released. As the name suggests, electron affinity is the ability of an atom to accept an electron. Unlike electronegativity, electron affinity is a quantitative measurement of the energy change that occurs when an electron is added to a neutral gas atom.
The more negative the electron affinity value, the higher an atom's affinity for electrons. Electron affinity increases upward for the groups and from left to right across periods of a periodic table because the electrons added to energy levels become closer to the nucleus, thus a stronger attraction between the nucleus and its electrons.
Remember that greater the distance, the less of an attraction; thus, less energy is released when an electron is added to the outside orbital. In addition, the more valence electrons an element has, the more likely it is to gain electrons to form a stable octet.
The less valence electrons an atom has, the least likely it will gain electrons. Electron affinity decreases down the groups and from right to left across the periods on the periodic table because the electrons are placed in a higher energy level far from the nucleus, thus a decrease from its pull.
However, one might think that since the number of valence electrons increase going down the group, the element should be more stable and have higher electron affinity. One fails to account for the shielding affect. As one goes down the period, the shielding effect increases, thus repulsion occurs between the electrons.
This is why the attraction between the electron and the nucleus decreases as one goes down the group in the periodic table. As you go down the group, first electron affinities become less in the sense that less energy is evolved when the negative ions are formed.
Fluorine breaks that pattern, and will have to be accounted for separately. Electron affinity generally increases across a period row in the periodic table, due to the filling of the valence shell of the atom. A trend of decreasing electron affinity down the groups in the periodic table would be expected since the additional electron is entering an orbital farther away from the nucleus.
Since this electron is farther away, it should be less attracted to the nucleus and release less energy when added. However, this trend applies only to Group-1 atoms. Electron affinity follows the trend of electronegativity : fluorine F has a higher electron affinity than oxygen O , and so on. Applications of Hard-Soft Acid-Base theory. Electron affinity generally increases across a period in the periodic table and sometimes decreases down a group. Electron affinity : The electron affinity of an atom or molecule is defined as the amount of energy released when an electron is added to a neutral atom or molecule to form a negative ion.
Electronegativity: The tendency of an atom or molecule to attract electrons to itself. Next Trial Session:. Recorded Trial Session. This is a recorded trial for students who missed the last live session. Waiting List Details:. Due to high demand and limited spots there is a waiting list.
You will be notified when your spot in the Trial Session is available. Electron affinity decreases down a group because the electrons are placed in higher energy levels in higher valence shells. This decreases the attraction of the nucleus on valence electrons via shielding. Less energy is released by the addition of an electron to caesium. This is because as caesium is larger, it has greater shielding, and a decreased pull of the nucleus on valence electrons. Across a period from left to right in the periodic table, the electron affinity increases.
This is because from left to right in a period, while shielding remains constant, the number of protons in the nucleus increases, increasing the nuclear charge and the influence of the nucleus on the outer electrons. Ions of Elements. Nuclear Charge of Atoms. Ionisation Energies. Electronegativity of the Elements. Nathan's subject matter ranges from general chemistry and organic chemistry. Nathan also created the curriculum on Breaking Atom in the course page.
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These are meitnerium Mt, atomic number , darmstadtium Ds, atomic number , roentgenium Rg, atomic number , nihonium Nh, atomic number , moscovium Mc, atomic number , livermorium Lv, atomic number and tennessine Ts, atomic number The post-transition metals are the ones found between the transition metals to the left and the metalloids to the right. Oganesson Og is a radioactive element that has the atomic number in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it.
It is in Group It has the symbol Og. Tennessine Ts is a radioactive element that has the atomic number in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it. It has the symbol Ts. Livermorium Lv is a radioactive element that has the atomic number in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it. It has the symbol Lv. Moscovium Mc is a radioactive metal that has the atomic number in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it.
It has the symbol Mc. Flerovium Fl is a radioactive metal that has the atomic number in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it.
It has the symbol Fl. Nihonium Nh is a radioactive metal that has the atomic number in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it. It has the symbol Nh. Copernicium Cr is a radioactive metal that has the atomic number in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it. It is a Transition metal in Group It has the symbol Rg. Roentgenium Rg is a radioactive metal that has the atomic number in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it.
Darmstadtium Ds is a radioactive metal that has the atomic number in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it. It has the symbol Ds. Meitnerium Mt is a radioactive metal that has the atomic number in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it.
It is a Transition metal in Group 9. It has the symbol Mt. Hassium Hs is a radioactive metal that has the atomic number in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it.
It is a Transition metal in Group 8. It has the symbol Hs. Bohrium Bh is a radioactive metal that has the atomic number in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it.
It is a Transition metal in Group 7. It has the symbol Bh. Seaborgium Sg is a radioactive metal that has the atomic number in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it.
It is a Transition metal in Group 6. It has the symbol Sg. Dubnium Db is a radioactive metal that has the atomic number in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it.
It is a Transition metal in Group 5. It has the symbol Db. Rutherfordium Rf is a radioactive metal that has the atomic number in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it. It is a Transition metal in Group 4. It has the symbol Rf. Lawrencium Lr is a silvery-white colored radioactive metal that has the atomic number in the periodic table.
It is an Actinoid Metal with the symbol Lr. Nobelium No is a radioactive metal that has the atomic number in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it. It is an Actinoid Metal with the symbol No. Mendelevium Md is a radioactive metal that has the atomic number in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it.
It is an Actinoid Metal with the symbol Md. Fermium Fm is a silvery-white colored radioactive metal that has the atomic number in the periodic table. It is an Actinoid Metal with the symbol Fm. Einsteinium Es is a silvery-white colored radioactive metal that has the atomic number 99 in the periodic table. It is an Actinoid Metal with the symbol Es. Californium Cf is a silvery-white colored radioactive metal that has the atomic number 98 in the periodic table.
It is an Actinoid Metal with the symbol Cf. Berkelium Bk is a silvery colored radioactive metal that has the atomic number 97 in the periodic table.
It is an Actinoid Metal with the symbol Bk.
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