Name: periodic trends in atomic size
Uploaded: 2020-09-03T13:38:28.000Z
Duration: 3 min 8 s
Channel: JoVE

K12 Standards

north-carolina-k-12-science-standard-course-of-study

North Carolina K-12 Science Standard Course of Study

9-12

Chemistry

Matter and its Interactions

PS.Chm.2.2

atomic-radii-and-effective-nuclear-charge

Atomic Radii and Effective Nuclear Charge

Die Größe eines Atoms wird von den Elektronen und ihrer Orbitale bestimmt. Orbitale beschreiben jedoch keinen begrenzten Raum, sondern vielmehr die statistische Wahrscheinlichkeit, wo ein Elektron gefunden werden kann. Wie ist also die atomare Größe definiert, und was beeinflusst sie?

Ein Atomradius kann auf zwei Arten beschrieben werden. Nichtbindender Atomradius oder van-der-Waals-Radius eines Atoms, ist die Hälfte des Abstands zwischen benachbarten Kernen im atomaren Festkörper. Umgekehrt, ein bindender Atomradius oder kovalenter Radius, unterscheidet zwischen Metallen und Nichtmetallen.

Bei Metallen wird der Radius für Atome in ihrer Kristallstruktur als die Hälfte des Abstands zwischen den Mittelpunkten von zwei benachbarte Atome beschrieben. Bei nichtmetallischen, zweiatomigen Molekülen, wird der Radius als die Hälfte des Abstands zwischen den Zentren von verbundenen Atomen beschrieben. Das Periodensystem stellt Variationen im kovalenten Radii dar, die oft als Atomradien bezeichnet werden, die von zwei Faktoren beeinflusst sind;die Anzahl der Hauptenergiezustände der Valenzelektronen und der effektiven Kernladung.

Die Entwicklung der Atomradien für die Elemente der Hauptgruppe abwärts der Spalten ist hier dargestellt. Nach unten in einer Gruppe, erhöht sich der Hauptquantenzahl n für jedes Element um eins. Somit gilt, dass je weiter die äußeren Elektronen vom Kern entfernt sind, nimmt der Atomradius in der Gruppe nach unten zu.

Zum Beispiel, entlang die Gruppe 1, steigt der Atomradius von Lithium zu Cäsium. Dieser Trend lässt sich am gesamten Periodensystem ablesen. Weiterhin zeigt die Darstellung, dass der Atomradius das Maximum für jedes Alkalimetall erreicht und fällt zum Minimum mit jedem Edelgas über der gesamten Periode.

Die abnehmenden Atomradien über eine Periode lassen sich durch die effektive Kernladung erklären. Erinnern Sie sich an das Konzept einer wirksamen Kernladung. In jedem Mehrfach-Elektronen-Atom schirmen die inneren Schalenelektronen die Elektronen der äußeren Schale von den Anziehungskräften des Zellkerns teilweise ab.

Also, bei der effektiven Kernladung, ist die von einem Außenelektron gefühlte Ladung geringer als die tatsächliche Kernladung. Elektronen in der gleichen Valenzhülle schirmen sich gegenseitig nicht sehr effektiv ab. In einer gesamten Periode steigt die nukleare Ladung, während die Anzahl der Elektronen der inneren Schale gleich bleiben.

Somit, nimmt die effektive Kernladung stetig zu, und die Abschirmung der Außenelektronen wird geringer, und dies führt zu einer Verringerung der Atomradien. Die Radien der meisten Übergangselemente, bleiben jedoch in jeder Reihe in etwa konstant. Das liegt daran, dass die Anzahl der Elektronen in den äußersten Hauptenergiezustandes nahezu konstant ist.

atomradien und effektive kernladung

Elemente der selben Gruppe des Periodensystems zeigen auch ein ähnliches chemisches Verhalten. Die Ähnlichkeit ist durch die gleichen Anzahl und Verteilung der Elektronen in den Valenzschalen der Elemente der selben Gruppe begründet

Wenn man eine Periode von links nach rechts durchläuft, wird mit jedem aufeinanderfolgenden Element ein Proton zum Kern und ein Elektron zur Valenzschale hinzugefügt. Geht man die Elemente einer Gruppe nach unten, bleibt die Anzahl der Elektronen in der Valenzschale konstant, aber die Hauptquantenzahl erhöht sich jedes Mal um eins. Ein Verständnis der elektronischen Struktur der Elemente ermöglicht es, einige der Eigenschaften zu untersuchen die ihr chemisches Verhalten bestimmen. Diese Eigenschaften variieren periodisch mit der Änderung der elektronischen Struktur der Elemente.

<h4>Variation des Atomradius</h4>

Die quantenmechanische Betrachtung macht es schwierig, eine eindeutige Größe eines Atoms festzulegen. Es gibt jedoch mehrere praktische Möglichkeiten, den Radius von Atomen zu definieren und so ihre relative Größe zu bestimmen, wobei trotz unterschiedlicher Methoden für das selbe Element ähnliche Werte gefunden werden.

Der Atomradius in Metallen beträgt die Hälfte des Abstands zwischen den Mittelpunkten zweier benachbarter Atome. Bei Elementen, die als zweiatomige Moleküle vorliegen, beträgt er die Hälfte des Abstands zwischen den Mittelpunkten der gebundenen Atome.

Wenn man sich entlang der Periode von links nach rechts bewegt, hat jedes Element im Allgemeinen einen kleineren Atomradius als das Element davor. Dies mag kontraintuitiv erscheinen, da es impliziert, dass Atome mit mehr Elektronen einen kleineren Atomradius haben. Dies lässt sich mit dem Konzept der effektiven Kernladung erklären. In jedem Mehrelektronenatom schirmen die Elektronen der inneren Hülle die Elektronen der äußeren Hülle teilweise vor der Anziehungskraft des Kerns ab. Somit ist die effektive Kernladung, die von einem Elektron empfundene Ladung, geringer als die tatsächliche Kernladung (Z) und kann wie folgt dargestellt werden:

Zeff = Z – σ

Dabei ist Zeff die effektive Kernladung, Z die tatsächliche Kernladung und σ die Abschirmungskonstante, wobei die Abschirmungskonstante größer als Null, aber kleiner als Z ist.

Jedes Mal, wenn wir entlang der Periode von einem Element zum nächsten gehen, erhöht sich Z um eins, aber die Abschirmung nimmt im Vergleich nur geringfügig zu. Daher nimmt Zeff mit jedem Schritt nach rechts weiter zu. Die stärkere Anziehungskraft (höhere effektive Kernladung), die die Elektronen auf der rechten Seite des Periodensystems erfahren, zieht sie näher an den Kern wodurch die Atomradien kleiner werden.

Kernelektronen schirmen die Elektronen in der äußersten Hauptebene wirksam von der Kernladung ab, die äußersten Elektronen untereinander haben jedoch keinen ähnlich starken Einfluss auf die Kernladung. Je größer die effektive Kernladung, desto stärker die Anziehung des Kerns auf die äußeren Elektronen und desto kleiner der Atomradius.

Die Radien einiger Übergangselemente bleiben allerdings über jede Reihe hinweg ungefähr konstant. Dies liegt daran, dass die Anzahl der Elektronen im äußersten Hauptenergieniveau nahezu konstant ist und sie eine annähernd gleiche effektive Kernladung erfahren.

Innerhalb jeder Periode nimmt der Atomradius mit zunehmendem Z ab; Innerhalb jeder Gruppe wird eine Zunahme des Atomradius mit steigendem Z beobachtet.

Beim Hinabschreiten einer Gruppe erhöht sich die Hauptquantenzahl n für jedes Element um eins. Dabei werden die Elektronen in immer größerer räumlicher Distanz zum Kern hinzugefügt.

Folglich muss die Größe des Atoms (und sein Atomradius) zunehmen, wenn wir den Abstand der äußersten Elektronen vom Kern vergrößern. Diese Beobachtung wird für die Atomradien der Halogene in der folgenden Tabelle veranschaulicht.

<table style="margin-left: auto; margin-right: auto;">
	<tbody style="border: 1px solid black;">
		<tr>
			<td colspan="3" style="color: black; border: 1px solid black; text-align: center;">Atomradien der Halogengruppenelemente</td>
		</tr>
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;">Atom</td>
			<td style="color: black; border: 1px solid black; text-align: center;">Atomradius (pm)</td>
			<td style="color: black; border: 1px solid black; text-align: center;">Kernladung, Z</td>
		</tr>
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;">F</td>
			<td style="color: black; border: 1px solid black; text-align: center;">64</td>
			<td style="color: black; border: 1px solid black; text-align: center;">9+</td>
		</tr>
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;">Cl</td>
			<td style="color: black; border: 1px solid black; text-align: center;">99</td>
			<td style="color: black; border: 1px solid black; text-align: center;">17+</td>
		</tr>
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;">Br</td>
			<td style="color: black; border: 1px solid black; text-align: center;">114</td>
			<td style="color: black; border: 1px solid black; text-align: center;">35+</td>
		</tr>
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;">I</td>
			<td style="color: black; border: 1px solid black; text-align: center;">133</td>
			<td style="color: black; border: 1px solid black; text-align: center;">53+</td>
		</tr>
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;">At</td>
			<td style="color: black; border: 1px solid black; text-align: center;">148</td>
			<td style="color: black; border: 1px solid black; text-align: center;">85+</td>
		</tr>
	</tbody>
</table>



Dieser Text wurde adaptiert von <a href="https://openstax.org/books/chemistry-2e/pages/6-5-periodic-variations-in-element-properties">Openstax Chemistry 2e, Section 6.5: Periodic Variations in Element Properties.</a>

Atomradien und effektive Kernladung

Die Elemente in Gruppen des Periodensystems zeigen ein ähnliches chemisches Verhalten. Diese Ähnlichkeit tritt auf, weil die Mitglieder einer Gruppe die gleiche Nummer ...

Education

Lehre

JoVE Core

Chemie

Eins

Periodic Properties of the Elements

Periodische Eigenschaften der Elemente

KEY TERMS AND CONCEPTS

KERNBEGRIFFE UND KONZEPTE

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 precision because atoms do not have a hard edge. Scientists use practical measurements instead. In metals, atomic radius is one-half the distance between the centers of two neighboring atoms. For elements that form diatomic molecules, it is one-half the distance between the centers of bonded atoms.

Moving from left to right across a period, atomic radius generally decreases. That may seem surprising because atoms on the right have more electrons. The reason is effective nuclear charge, or the charge an electron feels from the nucleus. It can be estimated as Z eff = Z – σ, where Z is the actual nuclear charge and σ is the shielding constant.

As Z increases by one from element to element across a period, shielding rises only a little. This means Z eff also increases from left to right. A stronger pull from the nucleus draws outer electrons closer, so the atomic radius becomes smaller. Core electrons shield outer electrons well, but outermost electrons do not shield one another very effectively. Some transition elements keep nearly the same radius across a row because the number of electrons in the outermost principal energy level changes very little, so the effective nuclear charge stays roughly constant.

The trend within a group is the opposite. Atomic radius increases as Z increases down a group. Each step down adds a principal energy level, so the outermost electrons are farther from the nucleus. That greater distance makes the atom larger. The halogens show this pattern clearly, with atomic radii increasing from fluorine to astatine.

Periodic Trends in Atomic Size

periodic classification of the elements

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...

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

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 why atomic radius changes across periods and groups, and how effective nuclear charge and shielding shape the size of atoms in the periodic table.

Periodic Trends in Atomic Size | JoVE K12

chemistry

JoVE Core Chemie erweckt allgemeine Konzepte der Chemie durch kompakte und leicht verständliche animierte Videolektionen zum Leben. Außerdem zeigen wir in den Videos Wissenschaftler in Aktion bei klassischen und neuartigen Forschungsexperimenten, wie sie heutzutage in Laboren weltweit durchgeführt wurden.

Physical Science

PS.PSc.1.6

Pennsylvania State Academic Standards

Chemical Reactions

3.2.9-12.C

Structure and Properties of Matter

3.2.9-12.A

Louisiana Student Standards for Science

High School

Matter And Its Interactions

HS-PS1-1

HS-PS1-2

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

Study Of Matter

Periodic trends of the elements

Structure And Properties Of Matter

Periodic Table

Tennessee Academic Standards

Matter and Its Interactions

CHEM1.PS1.12

Virginia  Standards of Learning

HIgh School

CH.2

CH.2.b

CH.2.c

PS.2

PS.2.b

PS.4

PS.4.a

PS.4.b

Minnesota Academic Standards in Science

3.1.1 9C.2.1.1.1

Arizona Science Standards

HS.P1

HS.P1U1.1

new-jersey-student-learning-standards-for-science

New Jersey Student Learning Standards for Science

Texas Essential Knowledge and Skills

CHEM.5

CHEM.5.A

CHEM.5.C

CHEM.7

CHEM.7.A

Alabama Course of Study Science

9-12.C.1.1

9-12.C.1.1.e

motion-and-stability-forces-and-interactions

Motion and Stability: Forces and Interactions

9-12.C.2.2.f

9-12.PS.3.4.b

Next Generation Science Standards

Florida Department of Education

SC.912.P.8

SC.912.P.8.5

Chemistry and Physics

IPC.7

IPC.7.B

new-york-state-science-learning-standards

New York State Science Learning Standards

HS. Structure and Properties of Matter

HS-PS1-1.

HS. Chemical Reactions

HS-PS1-2.

Georgia Standards of Excellence

SPS1.

Periodic Table Trends

SC1.

periodic-table-trends-atomic-radii-ionization-and-electronegativity

Periodic Table Trends: Atomic Radii, Ionization, and Electronegativity

Scientific Laws and Theories

Scientific Laws

In science, a law is defined as a concise, verbal or mathematical, statement that summarizes a vast number of experimental observations. ...

The Scientific Method

Chemistry is an empirical science. Scientists often pose questions to understand the chemistry in everyday life and seek answers to these questions. To ...

Classifying Matter by State

Chemistry is the study of matter and the changes it undergoes. Matter is anything that has mass and occupies space. Matter is all around us; the air, ...

Classifying Matter by Composition

Matter: Pure Substances and Mixtures
According to its composition, the matter can be classified into two broad categories &mdash; pure substances and ...

The Atomic Theory of Matter

The earliest recorded discussion of the basic structure of matter comes from ancient Greek philosophers. Leucippus and Democritus argued that all matter ...

Subatomic Particles

Dalton was only partially correct about the particles that make up matter. All matter is composed of atoms, and atoms are composed of three smaller ...

Elements: Chemical Symbols and Isotopes

A chemical symbol is an abbreviation used to indicate an element or an atom of an element. For example, the symbol for mercury is Hg. The same symbol is ...

Use models to explain how the scientific understanding of atomic structure has evolved.

PS.Chm.1.1

Radioactivity and Nuclear Equations

Nuclear chemistry is the study of reactions that involve changes in nuclear structure. The nucleus of an atom is composed of protons and, except for ...

Types of Radioactivity

The most common types of radioactivity are &#945; decay, &#946; decay, &#947; decay, neutron emission, and electron capture.
Alpha (&#945;) decay is the ...

Nuclear Stability

Protons and neutrons, collectively called nucleons, are packed together tightly in a nucleus. With a radius of about 10&#8722;15 meters, a nucleus is ...

Nuclear Binding Energy

The difference between the calculated and experimentally measured masses is known as the mass defect of the atom. In the case of helium-4, the mass defect ...

Radioactive Decay and Radiometric Dating

Radioactivity is a spontaneous disintegration of an unstable nuclide and is a random process, as all the nuclei in the sample do not decay simultaneously. ...

Nuclear Fission

Many heavier elements with smaller binding energies per nucleon can decompose into more stable elements that have intermediate mass numbers and larger ...

Nuclear Power

Controlled nuclear fission reactions are used to generate electricity. Any nuclear reactor that produces power via the fission of uranium or plutonium by ...

Nuclear Fusion

The process of converting very light nuclei into heavier nuclei is also accompanied by the conversion of mass into large amounts of energy, a process ...

Nuclear Transmutation

Nuclear transmutation is the conversion of one nuclide into another. It can occur by the radioactive decay of a nucleus, or the reaction of a nucleus with ...

Use models to compare nuclear reactions including alpha decay, beta decay and gamma decay; nuclear fusion and nuclear fission.

PS.Chm.1.2

Atomic Orbitals

An atomic orbital represents the three-dimensional regions in an atom where an electron has the highest probability to reside. The radial distribution ...

The Pauli Exclusion Principle

The arrangement of electrons in the orbitals of an atom is called its electron configuration. We describe an electron configuration with a symbol that ...

The Energies of Atomic Orbitals

In an atom, the negatively charged electrons are attracted to the positively charged nucleus. In a multielectron atom, electron-electron repulsions are ...

The Aufbau Principle and Hund's Rule

To determine the electron configuration for any particular atom, we can build the structures in the order of atomic numbers. Beginning with hydrogen, and ...

electron-configuration-of-multielectron-atoms

Electron Configuration of Multielectron Atoms

The alkali metal sodium (atomic number 11) has one more electron than the neon atom. This electron must go into the lowest-energy subshell available, the ...

Use models to explain how electrons are distributed in atoms.

PS.Chm.1.3

Periodic Classification of the Elements

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

The Periodic Table

As early chemists discovered more elements, they realized that various elements could be grouped by their similar chemical behaviors. One such grouping ...

Atomic Mass

Atoms &mdash; and the protons, neutrons, and electrons that compose them &mdash; are extremely small. For example, a carbon atom weighs less than 2 ...

Molar Mass

The identity of a substance is defined not only by the types of atoms or ions it contains but by the quantity of each type of atom or ion. For example, ...

Use the Periodic Table as a model to predict the relative properties of elements based on the pattern of valence electrons in the outermost energy levels of atoms.

PS.Chm.2.1

The elements in groups of the periodic table exhibit similar chemical behavior. This similarity occurs because the members of a group have the same number ...

Ionic Radii

Ionic radius is the measure used to describe the size of an ion. A cation always has fewer electrons and the same number of protons as the parent atom; it ...

Ionization Energy

The amount of energy required to remove the most loosely bound electron from a gaseous atom in its ground state is called its first ionization energy ...

Electron Affinity

The electron affinity (EA) is the energy change for adding an electron to a gaseous atom to form an anion (negative ion).



This process can be either ...

Construct an explanation to infer the atomic size, reactivity, electronegativity, and ionization energy of an element based on its position in the Periodic Table.

Types of Chemical Bonds

Chemical bonding theories were pioneered by American chemist Gilbert&#xA0;N. Lewis. He developed a model called the Lewis model to explain the type and ...

Lewis Symbols and the Octet Rule

Chemical bonds are complex interactions between two or more atoms or ions, which reduce the potential energy of the molecule. Gilbert N. Lewis developed a ...

Ionic Bonding and Electron Transfer

Ions are atoms or molecules bearing an electrical charge. A cation (a positive ion) forms when a neutral atom loses one or more electrons from its valence ...

The Born-Haber Cycle

Lattice Energy&#xA0;

An ionic compound is stable because of the electrostatic attraction between its positive and negative ions. The lattice energy of a ...

trends-in-lattice-energy-ion-size-and-charge

Trends in Lattice Energy: Ion Size and Charge

An ionic compound is stable because of the electrostatic attraction between its positive and negative ions. The lattice energy of a compound is a measure ...

Analyze and interpret data to explain the mechanisms and properties of the two main types of intramolecular (ionic and covalent) bonds.

PS.Chm.3.1

Analyze the structure of atoms and isotopes.

Periodic Trends in Atomic Size

Description

Transcript

Tags

More videos by Standards