Which Family of Elements Contains a Full Outer Shell of Electrons
Learning Outcomes
- Define the octet rule and its role in chemical bonds
Not all elements have enough electrons to fill their outermost shells, but an atom is at its most stable when all of the electron positions in the outermost shell are filled. Considering of these vacancies in the outermost shells, we run into the germination of chemic bonds, or interactions betwixt ii or more of the same or different elements that result in the formation of molecules. To accomplish greater stability, atoms will tend to completely make full their outer shells and will bond with other elements to accomplish this goal past sharing electrons, accepting electrons from another atom, or altruistic electrons to some other atom. Because the outermost shells of the elements with low diminutive numbers (up to calcium, with atomic number twenty) can hold eight electrons, this is referred to as the octet rule. An element can donate, accept, or share electrons with other elements to fill its outer shell and satisfy the octet rule.
An early model of the cantlet was developed in 1913 by the Danish scientist Niels Bohr (1885–1962). The Bohr model shows the atom as a central nucleus containing protons and neutrons, with the electrons in circular electron shells at specific distances from the nucleus, similar to planets orbiting around the dominicus. Each electron shell has a different energy level, with those shells closest to the nucleus being lower in energy than those farther from the nucleus. By convention, each shell is assigned a number and the symbol n—for example, the electron shell closest to the nucleus is called 1n. In order to move between shells, an electron must blot or release an corporeality of energy respective exactly to the difference in free energy betwixt the shells. For instance, if an electron absorbs energy from a photon, it may go excited and move to a higher-energy shell; conversely, when an excited electron drops dorsum down to a lower-free energy shell, it will release free energy, ofttimes in the course of oestrus.
Bohr model of an atom, showing free energy levels as concentric circles surrounding the nucleus. Energy must be added to motion an electron outward to a higher energy level, and energy is released when an electron falls down from a higher energy level to a closer-in ane. Epitome credit: modified from OpenStax Biology
Atoms, like other things governed by the laws of physics, tend to have on the lowest-free energy, about stable configuration they tin. Thus, the electron shells of an atom are populated from the inside out, with electrons filling up the low-energy shells closer to the nucleus before they move into the higher-free energy shells further out. The beat out closest to the nucleus, 1n, can hold two electrons, while the next beat, 2n, tin can concur 8, and the third shell, 3n, tin can hold up to eighteen.
The number of electrons in the outermost trounce of a particular cantlet determines its reactivity, or tendency to grade chemical bonds with other atoms. This outermost shell is known every bit thevalence shell, and the electrons constitute in it are calledvalence electrons. In general, atoms are most stable, least reactive, when their outermost electron crush is full. Most of the elements of import in biology need viii electrons in their outermost trounce in order to exist stable, and this rule of thumb is known as theoctet rule. Some atoms tin be stable with an octet even though their valence shell is the 3n trounce, which can agree up to 18 electrons. We will explore the reason for this when we discuss electron orbitals below.
Examples of some neutral atoms and their electron configurations are shown below. In this table, you tin can run across that helium has a full valence beat out, with two electrons in its starting time and but, 1n, shell. Similarly, neon has a consummate outer 2n trounce containing viii electrons. These electron configurations make helium and neon very stable. Although argon does not technically have a full outer vanquish, since the 3n trounce can hold up to eighteen electrons, it is stable like neon and helium because it has eight electrons in the 3n trounce and thus satisfies the octet rule. In contrast, chlorine has only seven electrons in its outermost vanquish, while sodium has just one. These patterns do not fill the outermost vanquish or satisfy the octet rule, making chlorine and sodium reactive, eager to gain or lose electrons to reach a more stable configuration.
Bohr diagrams signal how many electrons make full each chief trounce. Group 18 elements (helium, neon, and argon) have a full outer, or valence, crush. A full valence beat is the most stable electron configuration. Elements in other groups accept partially filled valence shells and gain or lose electrons to achieve a stable electron configuration.
Electron configurations and the periodic table
Elements are placed in order on the periodic table based on their atomic number, how many protons they have. In a neutral atom, the number of electrons will equal the number of protons, so we can easily determine electron number from atomic number. In addition, the position of an chemical element in the periodic table—its cavalcade, or group, and row, or period—provides useful information about how those electrons are arranged.
If we consider merely the first 3 rows of the table, which include the major elements important to life, each row corresponds to the filling of a different electron trounce: helium and hydrogen place their electrons in the 1n shell, while second-row elements like Li outset filling the 2n shell, and third-row elements similar Na proceed with the 3n beat out. Similarly, an chemical element's cavalcade number gives information about its number of valence electrons and reactivity. In general, the number of valence electrons is the same within a column and increases from left to right within a row. Grouping one elements have just one valence electron and group eighteen elements accept eight, except for helium, which has only two electrons full. Thus, grouping number is a practiced predictor of how reactive each element will be:
- Helium (He), neon (Ne), and argon (Ar), every bit group 18 elements, take outer electron shells that are full or satisfy the octet dominion. This makes them highly stable as single atoms. Because of their not-reactivity, they are called theinert gases ornoble gases.
- Hydrogen (H), lithium (Li), and sodium (Na), equally group 1 elements, have just i electron in their outermost shells. They are unstable as single atoms, but tin get stable by losing or sharing their one valence electron. If these elements fully lose an electron—every bit Li and Na typically do—they become positively charged ions: Li+, Na+.
- Fluorine (F) and chlorine (Cl), as group 17 elements, have 7 electrons in their outermost shells. They tend to attain a stable octet by taking an electron from other atoms, becoming negatively charged ions: F− and Cl−.
- Carbon (C), as a group 14 element, has iv electrons in its outer shell. Carbon typically shares electrons to attain a complete valence beat, forming bonds with multiple other atoms.
Thus, the columns of the periodic table reverberate the number of electrons found in each element's valence crush, which in turn determines how the chemical element will react.
Try Information technology
Contribute!
Did you have an idea for improving this content? We'd love your input.
Improve this pageLearn More
Source: https://courses.lumenlearning.com/wm-nmbiology1/chapter/chemical-bonding/
0 Response to "Which Family of Elements Contains a Full Outer Shell of Electrons"
แสดงความคิดเห็น