Name: how valence electrons shape the periodic table
Uploaded: 2020-09-03T13:38:28.000Z
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Periodic Classification of the Elements

De elektronen die de buitenste schil van een atoom bezetten, zijn valentie-elektronen, terwijl elektronen die de binnenste hoofdenergieniveaus bezetten kernelektronen zijn. Een natriumatoom met een 3s1-elektronenconfiguratie heeft drie hoofdenergieniveaus. De volledige innerlijke hoofdenergieniveaus met 2s22p6 geven aan dat er tien kernelektronen zijn, gevolgd door het derde buitenste niveau dat het resterende ene elektron bevat.Daarom heeft natrium één valentie-elektron. Evenzo heeft chloor tien kernelektronen en zeven valentie-elektronen. Valentie-elektronen bevinden zich het verst van de kern en worden het meest losjes vastgehouden.Daarom zijn ze het gemakkelijkst te verliezen of te delen en spelen ze een belangrijke rol bij chemische binding. Elementen met hetzelfde aantal valentie-elektronen vertonen vergelijkbare chemische eigenschappen, zoals te zien is in de opstelling in het moderne periodiek systeem. Voor hoofdgroepelementen is het geletterde groepsnummer gelijk aan het aantal valentie-elektronen en is het rijnummer gelijk aan het hoogste hoofdkwantumgetal van dat element.Elk element in een groep heeft hetzelfde aantal elektronen beschikbaar voor binding. Onderaan de groep neemt het belangrijkste kwantumgetal met één toe, terwijl het aantal valentie-elektronen hetzelfde blijft. De twee uiterst linkse kolommen van het periodiek systeem vormen het s-blok.Voor deze elementen gaat het laatste elektron een s-orbitaal binnen. Groep één elementen behalve waterstof worden de alkalimetalen genoemd en zijn extreem reactief omdat ze slechts één valentie-elektron hebben. Groep twee elementen zijn de aardalkalimetalen met twee elektronen in de valentieschil.De zes uiterst rechtse kolommen vormen het p-blok. De valentieschil van deze elementen heeft de s-orbitalen volledig bezet en het laatste elektron komt de p-orbitaal binnen. Van groep drie A tot groep acht A neemt het aantal elektronen in p-orbitalen met één toe.De edelgassen hebben acht valentie-elektronen behalve helium, dat tot het s-blok behoort, en slechts twee elektronen heeft. Het d-blok bestaat uit de tien kolommen die tussen het s-en p-blok zijn geplaatst. Deze elementen worden de overgangsmetalen genoemd.Het laatste elektron komt de d-orbitaal van de hoofdschil één minder binnen dan het rijnummer. In de vierde rij vullen 3d-orbitalen zich, in de vijfde rij vullen 4d-orbitalen zich, enzovoort. Binnenste overgangselementen vormen het f-blok en laten het laatste elektron een f-orbitaal binnengaan.Het hoofdkwantumgetal van de f-orbitalen die in elke rij worden gevuld, is twee minder dan het rijnummer. In de zesde rij vullen de vier f-orbitalen zich en in de zevende rij vullen de vijf f-orbitalen zich. Binnenste overgangselementen zijn gerangschikt in de lanthanidenreeks en de actinidenreeks.Het aantal kolommen in elk blok geeft aan hoeveel elektronen er in het subniveau van het blok kunnen worden gevuld. Twee kolommen in het s-blok correleren met een s-orbitaal met twee elektronen, zes kolommen in het p-blok vertegenwoordigen drie p-orbitalen met zes elektronen, terwijl tien kolommen in het d-blok overeenkomen met vijf d-orbitalen met elk twee elektronen. Ten slotte bestaat het f-blok uit veertien kolommen die de maximale capaciteit van zeven f-orbitalen aangeven.

periodieke classificatie van de elementen

Het periodiek systeem rangschikt atomen op basis van toenemend atoomnummer, zodat elementen met dezelfde chemische eigenschappen periodiek terugkeren. Wanneer hun elektronenconfiguraties aan de tabel worden toegevoegd, wordt een periodieke herhaling van vergelijkbare elektronenconfiguraties in de buitenste schillen van deze elementen waargenomen. Omdat ze zich in de buitenste schil van een atoom bevinden, spelen valentie-elektronen de belangrijkste rol bij chemische reacties. De buitenste elektronen hebben de hoogste energie van de elektronen in een atoom en gaan gemakkelijker verloren of worden gedeeld dan de kernelektronen. Valentie-elektronen zijn ook de bepalende factor in sommige fysische eigenschappen van de elementen. De horizontale rijen staan bekend als punten. Gedurende een bepaalde periode heeft elk opeenvolgend element een extra proton in de atoomkern en een extra elektron in de valentieschil. De verticale kolommen zijn groepen. Elementen in een bepaalde groep (of kolom) hebben hetzelfde aantal valentie-elektronen (Figuur 1); de alkalimetalen lithium en natrium hebben elk slechts één valentie-elektron, de aardalkalimetalen beryllium en magnesium hebben elk twee, en de halogenen fluor en chloor hebben elk zeven valentie-elektronen. Het is het verlies, de winst of het delen van valentie-elektronen die bepalen hoe elementen reageren. De gelijkenis in chemische eigenschappen tussen elementen van dezelfde groep treedt op omdat ze hetzelfde aantal valentie-elektronen hebben. Het is belangrijk om te onthouden dat het periodiek systeem werd ontwikkeld op basis van het chemische gedrag van de elementen, lang voordat er enig idee van hun atomaire structuur beschikbaar was. Nu wordt de opstelling van het periodiek systeem begrepen; elementen waarvan de atomen hetzelfde aantal valentie-elektronen hebben, bevinden zich in dezelfde groep. De gekleurde delen van Figuur 1 tonen de drie categorieën elementen, ingedeeld naar de orbitalen die worden gevuld. <img alt="Eq1" src="https://www.jove.com/files/core/CDNSource/lessons/1046/1046Image_1v2.png"> Figuur 1: Deze versie van het periodiek systeem toont de configuratie van elk element. Merk op dat de configuratie in elke groep vaak vergelijkbaar is. Hoofdgroepelementen worden soms representatieve elementen genoemd. Dit zijn de elementen waarin het laatst toegevoegde elektron een s- of p-orbitaal in de buitenste schil binnengaat, weergegeven in blauw en rood in figuur 1. Deze categorie omvat alle niet-metalen elementen, evenals de metalloïden en veel metalen. De valentie-elektronen voor hoofdgroepelementen zijn die met het hoogste n-niveau. Gallium (Ga, atoomnummer 31) heeft bijvoorbeeld de elektronenconfiguratie [Ar]4s23d104p1, die drie valentie-elektronen bevat (onderstreept). De volledig gevulde d-orbitalen tellen als kernelektronen, niet als valentie. De twee uiterst linkse kolommen vormen het s-blok en de zes uiterst rechtse kolommen vormen het p-blok. De edelgassen, die deel uitmaken van het p-blok, hebben allemaal acht valentie-elektronen, behalve helium, dat er twee heeft. Deze elementen zijn zeer stabiel en niet-reactief. Overgangselementen of overgangsmetalen: Dit zijn metalen elementen waarin het laatst toegevoegde elektron een d-orbitaal binnengaat. De valentie-elektronen (die toegevoegd na de laatste edelgasconfiguratie) in deze elementen omvatten de ns- en (n – 1) d-elektronen. De officiële IUPAC-definitie van overgangselementen specificeert die met gedeeltelijk gevulde d-orbitalen. De elementen met volledig gevulde orbitalen (Zn, Cd, Hg, evenals Cu, Ag en Au in Figuur 1) zijn dus technisch gezien geen overgangselementen. De term wordt echter vaak gebruikt om te verwijzen naar het gehele d-blok (geel gekleurd in figuur 1). Het d-blok bestaat uit 10 kolommen. Het belangrijkste kwantumgetal van de d-orbitalen die elke rij vullen, is gelijk aan het rijnummer min één. In de vierde rij vullen 3D-orbitalen, in de vijfde rij vullen 4D-orbitalen, enzovoort. Binnenste overgangselementen: Ze worden in het groen weergegeven in Figuur 1. De valentieschillen van de binnenste overgangselementen bestaan uit de (n – 2)f, de (n – 1)d en de ns-subschalen. Binnenste overgangselementen vormen een f-blok wanneer het laatste elektron een f-orbitaal binnengaat. Het belangrijkste kwantumgetal van de f-orbitalen die elke rij vullen, is gelijk aan het rijnummer minus twee. In de zesde rij vullen de 4f-orbitalen zich, en in de zevende rij vullen de 5f-orbitalen. Er zijn twee innerlijke overgangsreeksen: <ol> <li>De lanthanidereeks: lanthanide (La) tot lutetium (Lu)</li> <li>De actinidenreeks: actinide (Ac) tot lawrencium (Lr)</li> </ol> Lanthaan en actinium zijn, vanwege hun overeenkomsten met de andere leden van de serie, opgenomen en gebruikt om de serie een naam te geven, ook al zijn het overgangsmetalen zonder f-elektronen.

Periodieke classificatie van de elementen

The periodic table arranges atoms based on increasing atomic number so that elements with the same chemical properties recur periodically. When their ...

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how valence electrons shape the periodic table

The periodic table organizes elements by increasing atomic number, and it also shows why elements in the same group behave alike. As the electron configurations are placed into the table, a repeating pattern appears in the outer shells of atoms. These outer electrons are called valence electrons, and they play the biggest role in chemical reactions. They are the highest-energy electrons in an atom, so they are easier to lose or share than core electrons. Valence electrons also help determine some physical properties of elements.

The horizontal rows on the periodic table are periods. Moving across a period, each next element has one more proton in the nucleus and one more electron in the valence shell. The vertical columns are groups. Elements in the same group have the same number of valence electrons, which is why they often show similar chemical behavior. For example, lithium and sodium each have one valence electron, beryllium and magnesium each have two, and fluorine and chlorine each have seven. Because elements react by losing, gaining, or sharing valence electrons, their group placement helps predict how they will behave.

It is important to remember that the periodic table was built from chemical behavior before atomic structure was understood. Today, the pattern makes sense because elements with the same number of valence electrons are placed in the same group. The colored regions of the table also show three categories based on which orbitals are being filled. Main group elements, also called representative elements, are the elements whose last added electron enters an s or p orbital in the outermost shell. This category includes all nonmetals, the metalloids, and many metals. For main group elements, the valence electrons are the electrons with the highest n level. Gallium, for example, has the electron configuration [Ar] 4s2 3d10 4p1, so it has three valence electrons. The filled d orbitals are counted as core electrons, not valence electrons.

The two far-left columns form the s-block, and the six far-right columns form the p-block. The noble gases are part of the p-block. They usually have eight valence electrons, except helium, which has two. This helps explain why noble gases are highly stable and unreactive. Transition elements, or transition metals, are metallic elements whose last added electron enters a d orbital. Their valence electrons include the ns and (n - 1)d electrons added after the last noble gas configuration. By the official IUPAC definition, transition elements have partially filled d orbitals, so Zn, Cd, Hg, and also Cu, Ag, and Au are not technically transition elements, even though the term is often used for the whole d-block.

The d-block has 10 columns. As you move across each row, the d orbitals that fill have a principal quantum number that is one less than the row number. In the fourth row, 3d orbitals fill; in the fifth row, 4d orbitals fill; and so on. Inner transition elements form the f-block, where the last electron added enters an f orbital. Their valence shells include the (n - 2)f, the (n - 1)d, and the ns subshells. The f orbitals that fill across each row have a principal quantum number that is two less than the row number. In the sixth row, 4f orbitals fill, and in the seventh row, 5f orbitals fill. The two inner transition series are the lanthanides, from lanthanum through lutetium, and the actinides, from actinium through lawrencium. Lanthanum and actinium are included in those series because they are similar to the other members, even though they are transition metals with no f electrons.

How Valence Electrons Shape the Periodic Table

how-valence-electrons-shape-the-periodic-table

periodic classification of the elements

The periodic table organizes elements by increasing atomic number, and it also shows why elements in the same group behave alike. As the electron configurations are placed into the table, a repeating pattern appears in the outer shells of atoms. These outer electrons are called valence electrons, and they play the biggest role in chemical reactions. They are the highest-energy electrons in an atom, so they are easier to lose or share than core electrons. Valence electrons also help determine...

ionization energy

Ionization Energy Trends in the Periodic Table

Ionization energy is the energy needed to remove an electron from a gaseous atom or ion in its ground state. The first ionization energy, or IE1, removes the most loosely bound electron and forms a 1+ cation. The second ionization energy, IE2, removes the next electron, and each later ionization energy removes another electron from the atom or ion. Ionization always requires energy, so these processes are endothermic. That means ionization energy values are always positive. In general, larger...

atomic radii and effective nuclear charge

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Periodic Trends in Atomic Size

Periodic trends in atomic size help explain why atoms get larger or smaller across the periodic table. Elements in the same group show similar chemical behavior because they have the same number and arrangement of valence electrons. Across a period, each new element adds one proton to the nucleus and one electron to the valence shell. Down a group, the number of valence electrons stays the same, but the principal quantum number increases by one. Atomic radius is not easy to define with perfect...

ionic radii

How Ionic Charge Changes Ion Size

Ionic radius describes the size of an ion. It changes when an atom gains or loses electrons. Cations are positive ions with fewer electrons than the parent atom, and they are smaller than the atoms they come from. Aluminum shows this pattern clearly. A neutral aluminum atom has a covalent radius of 118 pm, while Al3+ has an ionic radius of 68 pm. When electrons are removed from the outer valence shell, the remaining core electrons feel a stronger effective nuclear charge, or Zeff. That pull...

electron affinity

Electron Affinity Trends on the Periodic Table

Electron affinity is the energy change that happens when a gaseous atom gains an electron and becomes a negative ion, or anion. For many elements, this process releases energy, so the electron affinity value is negative. For some elements, energy must be added instead, so the value is positive. Electron affinity also applies when more than one electron is added. The second electron affinity is the energy change for adding an electron to an anion to make a 2− ion. Later electron affinities...

alkali metals

Alkali Metals: Reactivity Trends

Alkali metals are Group 1 elements with one valence electron. They are soft, shiny metallic solids that are malleable, ductile, and good conductors of heat and electricity. Their melting points are unusually low for metals and drop as you move down the group. Density generally increases down the group, except for potassium. The trend in atomic size helps explain their behavior. Moving from lithium to cesium, each element has a higher principal quantum number, so the outer electron is farther...

halogens

Halogens: Trends and Reactions

Halogens are Group 17 nonmetals that show clear trends in structure and reactivity. At room temperature, fluorine and chlorine are gases, bromine is a liquid, and iodine is a solid. Astatine is highly unstable and radioactive, so most of its properties are still unknown because it has a very short half-life. Tennessine is a synthetic element that is also predicted to belong to this group. These elements do not usually exist as single atoms. Instead, they form diatomic molecules, which means...

noble gases

Noble Gases: Sources, Uses, and Reactions

Noble gases are the group 18 elements helium, neon, argon, krypton, xenon, and radon. They were called “noble” because they were once thought to be nonreactive. That idea changed in 1962, when Dr. Neil Bartlett at the University of British Columbia showed that this assumption was not fully correct. These gases occur in very small amounts in the atmosphere. Some natural gas contains 1–2% helium by mass. Helium is separated from natural gas by removing the condensable components, which leaves...

key terms and concepts

Learn how valence electrons explain periodic table groups, blocks, and element behavior, including main group, transition, lanthanide, and actinide elements.

How Valence Electrons Shape the Periodic Table | JoVE K12

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How Valence Electrons Shape the Periodic Table

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