Electron Shells
Electron shells are energy levels within an atom where electrons are found. These shells are designated by letters (K, L, M, etc.) and can hold a specific number of electrons. The innermost shell, K, can hold up to 2 electrons, while subsequent shells can hold more. The arrangement of electrons in these shells determines an atom's chemical properties.
7 Key excerpts on "Electron Shells"
- Kevin Reel, Derrick C. Wood, Scott A. Best(Authors)
- 2014(Publication Date)
- Research & Education Association(Publisher)
...Take the sum of each isotope’s contribution to compute the average atomic mass. Electrons Electrons reside in regions outside of the nucleus known as atomic orbitals. These atomic orbitals can have a variety of shapes and represent the most probable region where an electron can be located. Electrons found in the outermost shells are known as valence electrons while electrons found closer to the nucleus are core electrons. TEST TIP An understanding of valence electrons and core electrons are essential in describing trends in the periodic table. Electrons in Atoms You may be wondering why so much attention is given to electrons. It is because that is where all of the most important chemistry resides! Thus, if you have an understanding of the electrons you will understand how chemistry, and indeed the world, works. There are different ways to model the location of electrons in atoms: electron configurations, orbital notation, and quantum numbers. Electron Configurations The electron configuration of an atom assigns the location of electrons with respect to the energy level and type of orbital in which the electron resides. The electron configuration is written with a number corresponding to the energy level (principal quantum number) and a letter (s, p, d, or f) that depicts the sublevel where the electron resides. The sublevels can be broken into groups within the periodic table called blocks. This is illustrated in Figure 5.3. A superscript is used after the letter to signify the number of electrons in that sublevel. Figure 5.3. Periodic Table Illustrating the Electron Configuration of Atoms The maximum number of electrons in a sublevel is based upon the type of sublevel as illustrated in the following table and Figure 5.4. Figure 5.4. Sublevels and the Maximum Number of Electrons It is easiest to write electron configurations utilizing the periodic table...
eBook - ePub- Jeffrey Gaffney, Nancy Marley(Authors)
- 2017(Publication Date)
- Elsevier(Publisher)
...nucleus in all atoms. Electron affinity the amount of energy released when an electron is added to a neutral atom in the gas phase. Electron dot structure a diagram of the valence electrons of an element where the electrons are represented by dots placed around the chemical symbol of the element. Electron shell a group of electron subshells all having the same value of the principal quantum number. Electron subshell a group of electron orbitals with the same value of the principal quantum number. Electronegativity a measure of the tendency of an atom to attract electrons from another atom in a chemical bond. Electronic configuration the assignment of the electrons in an atom to electronic shells, subshells, and orbitals. Excited state higher energy state of an atom arising from the absorption of energy and the transition of electrons to higher orbitals. Ground state the lowest possible energy state of an atom. Groups vertical columns in the Periodic Table of the Elements. Hund's Rule electrons will occupy orbitals individually before filling them in pairs. Ion an atom with an unequal number of protons and electrons. Ionization the process of creating an ion from an uncharged atom. Ionization energy the amount of energy required to remove an electron from an atom in the gas...
eBook - ePub- Richard J. D. Tilley(Author)
- 2019(Publication Date)
- Wiley(Publisher)
...Appendix D Atomic Electron Configurations and Energy Levels D.1 Electron Configurations of the Lighter Atoms For most chemical purposes, an atom or an ion can be considered to consist of a dense minute nucleus surrounded by electrons, which are said to occupy a series of orbitals. The electron configuration of an atom or an ion describes the way in which these electrons are allocated to these orbitals. The simplest approximation that gives the occupancy of the orbitals is the independent particle model (the one-electron model, the orbital approximation), in which each electron is supposed to be isolated and moving in a field comprising of that arising in the nucleus and all of the other electrons combined. In this approach, each electron is assigned a set of four unique quantum numbers that correspond to the atomic orbital that the electron occupies. The atomic orbitals form a set of shells that are filled from the lowest energy upwards. The Pauli exclusion principle demands that only two electrons, with opposed spins, can occupy an orbital. If this were not so, all electrons would end up in the lowest energy orbital. The lowest energy shell is characterised by a principal quantum number 1 and contains only one atomic orbital called an s-orbital. This, like any atomic orbital, can contain either one or two electrons. The two atoms that these two alternatives correspond to are hydrogen (H) and helium (He). The electron configurations of these two atoms are written: H 1 s 1 He 1 s 2 where the principal quantum number (1) is written first, the orbital (s) follows, and then the number of electrons in the orbital is a superscript. The next lowest energy shell is characterised by a principal quantum number 2 and contains one s -orbital and three p-orbitals, p x, p y, and p z, all of which have the same energy. The s -orbital can contain up to two electrons, as above, and the three p -orbitals can contain a maximum of six electrons...
eBook - ePubChemistry
Concepts and Problems, A Self-Teaching Guide
- Richard Post, Chad Snyder, Clifford C. Houk(Authors)
- 2020(Publication Date)
- Jossey-Bass(Publisher)
...Later, we will use this arrangement in discussing chemical bonding, chemical reactions, and chemical properties. QUANTUM ATOMIC MODEL The model we discuss has evolved from the study of quantum mechanics (a theoretical mathematical approach to the study of atomic and molecular structure). We do not attempt an in-depth presentation here. Instead, we present some of the basic concepts so you may use them later in this book or build upon them in other chemistry courses. Keep in mind that we are studying the basic model of a very complex theory. A good way to help you remember the model is to compare it to an apartment building. An apartment building has different floors, different apartments on each floor, and different rooms within each apartment. We can look upon the electrons of an atom as rather peculiar apartment dwellers. Electrons prefer the floor closest to the ground and the smallest apartments. Electrons also prefer to live one to a room until each room in an apartment has one occupant. The electrons will then pair up until each room has two. Each room in the apartment can hold only two electrons. Apartment buildings may have several floors. The model we discuss has several floors, but only the first seven floors will be occupied. All the electrons of the elements known today will fit within seven floors of the building. Additional floors are available but will be occupied only in special cases. The floors in the apartment building are called shells in the electron model and are numbered 1 through 7. According to what you have just read, what shell will be occupied first by electrons? _________ Answer: shell 1 (the first floor) Each shell (or floor) in the model has one or more apartments, which are called subshells. These subshells are apartments of four sizes: s, p, d, and f. An s subshell (apartment) has only a single room. A p subshell has three rooms. A d subshell has five rooms, while an f subshell has seven rooms...
eBook - ePub- Suzanne Easton(Author)
- 2012(Publication Date)
- Wiley-Blackwell(Publisher)
...If there are not enough electrons to fill the shell, then the odd electrons will be found in the outermost shell. Each shell has a maximum number of electrons that it can hold, before the next shell is entered. If the outer shell is full, the atom will be stable. If the outer shell is not full, the atom will attempt to gain electrons to fill the outer shell. This will make the atom unstable. Elements such as copper or tungsten, which are good conductors of heat and electricity, will have a single electron in the outer shell, which leaves easily and can act as a free electron. Table 3.2 Number of electrons in atomic shells. Shell number Shell letter Maximum number of electrons 1 K 2 2 L 8 3 M 18 4 N 32 The maximum number of electrons in each shell is calculated using 2 n 2, where n equals the shell number. The periodic table All elements known to man are arranged in the periodic table. This table displays all the elements in groups according to their chemical and physical properties. Group I is composed of the alkali metals (excluding hydrogen), which combine easily with oxygen and react violently with water. Elements in Group VIII are called the noble gases. These do not react with other elements easily. By convention, the periodic table will show the atomic mass and atomic number of every element. The atomic number will always be above the symbol for the element and the mass number will always be below the element symbol (Figure 3.2). Using the periodic table, the number of electrons, protons and neutrons in an atom can be calculated. Figure 3.2 Single unit from the periodic table (copper). Proton or atomic number Symbol : Z The atomic number represents the number of protons in the nucleus of an atom. An atom with just one proton is hydrogen. If the nucleus contains eight protons, then the atom is oxygen, and if it has 56 protons, then it is barium...
eBook - ePub- Tony Cox(Author)
- 2004(Publication Date)
- Taylor & Francis(Publisher)
...The electron configuration specifies the occupancy of orbitals, each of which has an associated energy. Electron spin Electrons have an intrinsic rotation called spin, which may point in only two possible directions, specified by a quantum number m s. Two electrons in the same orbital with opposite spin are paired. Unpaired electrons give rise to paramagnetism. Pauli exclusion principle When the spin quantum number m s is included, no two electrons in an atom may have the same set of quantum numbers. Thus a maximum of two electrons can occupy any orbital. Effective nuclear charge The electrostatic repulsion between electrons weakens their binding in an atom; this is known as screening or shielding. The combined effect of attraction to the nucleus and repulsion from other electrons is incorporated into an effective nuclear charge. Screening and penetration An orbital is screened more effectively if its radial distribution does not penetrate those of other electrons. For a given n, s orbitals are least screened and have the lowest energy; p, d, … orbitals have successively higher energy. Hund’s first rule When filling orbitals with l > 0, the lowest energy state is formed by putting electrons so far as possible in orbitals with different m values, and with parallel spin. Related topics Atomic orbitals (A2) Molecular orbitals: homonuclear diatomics (C4) The orbital approximation Schrödinger’s equation cannot be solved exactly for any atom with more than one electron. Numerical solutions using computers can be performed to a high degree of accuracy, and these show that the equation does work, at least for fairly light atoms where relativistic effects are negligible (see Topic A5). For most purposes it is an adequate approximation to represent the wavefunction of each electron by an atomic orbital similar to the solutions for the hydrogen atom...
eBook - ePubFoundations for Teaching Chemistry
Chemical Knowledge for Teaching
- Keith S. Taber(Author)
- 2019(Publication Date)
- Routledge(Publisher)
...In effect, we often teach this material ahistorically, from a position of knowledge about atomic and molecular structures that can explain valencies and stoichiometry (e.g., carbon [that is, a carbon atom] can form four covalent bonds with chlorine [that is, chlorine atoms], but nitrogen only three). Periodic table concepts As well as being an abstract concept in its own right, the periodic table concept subsumes some other specific concepts. Students may be introduced to ‘blocks’ (the s-block, etc.) which can be understood in terms of identifiable geometric units in the table – building blocks from which the table is composed – or may be understood in terms of the specifics of a model of atomic structure. Often at the point where learners are introduced to the s, p, and d blocks of the periodic table they have only been taught a model of electronic structure of the atoms in terms of concentric shells of electrons around the nucleus, so at that point the links to different energy levels within ‘shells’ (so called sub-shells) or different geometries of atomic orbital cannot be made. Two other concepts, however, can be linked more directly to a model of atomic structure – at least for the first 20 elements. The periodic table is arranged into rows known as periods and columns known as groups. That geometric notion links to atomic structure (so an element in period 2 has atoms with two occupied shells of electrons; an atom of an element in group 3 has three electrons in its outer shell – and so the element in period 2 and group 3, B, has an electronic configuration of 2.3). This also relates to periodicity. Elements in the same group are said to share common properties, whilst there are often clear trends in properties moving across periods. Common group properties Those common group properties and periodic trends reflect certain patterns abstracted from a vast catalogue of data...
