Chemistry
Atomic Structure
Atomic structure refers to the arrangement of protons, neutrons, and electrons within an atom. At the center of the atom is the nucleus, which contains protons and neutrons, while electrons orbit around the nucleus in specific energy levels or shells. Understanding atomic structure is crucial in explaining the behavior and properties of elements and their interactions in chemical reactions.
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10 Key excerpts on "Atomic Structure"
eBook - PDFChemistry for Technologists
The Commonwealth and International Library: Electrical Engineering Division
- G. R. Palin, N. Hiller(Authors)
- 2014(Publication Date)
- Pergamon(Publisher)
SECTION II STRUCTURAL CHEMISTRY This page intentionally left blank CHAPTER 2 Atomic Structure Fundamental Particles The original concept of the atom was that it was an indivisible entity, and that the different atoms which occurred in nature were the basic units from which all matter was made. Later, when it was found that the atom was divisible, it was concluded that each atom was made up from pro-tons, neutrons and electrons as stated in Section I. These were called fundamental particles, and it seemed that all matter was made up from these three basic units, combined first into atoms of the various elements, which in turn combined to give all other substances. More recently many more sub-atomic particles have been discovered, and these are also called fundamental. The use of this term in this context has also changed. It is now used to denote particles whose structure is not understood in detail, although there is evidence of a structure for many of them, including pro-tons and neutrons. Despite these more recent discoveries, the picture of the atom as a central nucleus of protons and neutrons surrounded by a cloud of electrons is adequate for most studies outside some specialist fields of physics. Isotopes As stated in Section I, the number of protons in an atom is the atomic number and equals the number of electrons. Atoms with atomic numbers from one to ninety-two occur naturally, and others with higher atomic numbers have been made artificially by nuclear reactions. The volume of the region occupied by the nucleus is very small compared with that oc-cupied by the electrons, and the effect of the nucleus on the electrons due to its mass is negligible compared with its effect due to its charge. The ar-rangement of the electrons in an atom is determined mainly by the charge on the nucleus and the number of electrons, and as these are both equal to the atomic number, all atoms with the same atomic number have the same electron arrangement.
eBook - PDFFoundations of Chemistry
An Introductory Course for Science Students
- Philippa B. Cranwell, Elizabeth M. Page(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
1 Atomic Structure At the end of this chapter, students should be able to: • Draw a representation of an atom, and determine how many protons, neu-trons, and electrons are present • Explain how electrons are arranged in atoms • Explain and draw s, p, and d orbitals • Give the ground state electronic configuration of an atom • Explain isotopes, and calculate the average atomic mass of an element from given isotopic ratios • Explain the process of radioactive decay, and give relevant equations 1.1 Atomic Structure This section will outline the structure of the atom, as well as introduce isotopes and radioisotopes of the elements. 1.1.1 Subatomic particles Understanding the atom is fundamental to being able to understand, and subse-quently master, chemistry. All elements are made up of atoms, and the exact structure of each atom determines which element it is. There are two main regions inside an atom: the nucleus and the outer shells surrounding the nucleus. Within the nucleus are two types of subatomic particles: protons and neutrons . The number of protons in an atom determines the actual element. The third main type of subatomic particle is found in the outer shells, and these are called elec-trons . Electrons are very small and are negatively charged, and they orbit the Foundations of Chemistry: An Introductory Course for Science Students , First Edition. Philippa B. Cranwell and Elizabeth M. Page. © 2021 John Wiley & Sons Ltd. Published 2021 by John Wiley & Sons Ltd. Companion website: www.wiley.com/go/Cranwell/Foundations nucleus rather like planets orbit the sun. The exact manner in which an electron orbits the nucleus is defined by the orbital the electron occupies. This will be dis-cussed in Section 1.2.4. Protons and neutrons have the same mass and are much larger and heavier than electrons. Protons have a positive charge, and neutrons have no charge and so are neutral. Both protons and neutrons are found in the nucleus of the atom (Figure 1.1).
eBook - PDF- Douglas P. Heller, Carl H. Snyder(Authors)
- 2015(Publication Date)
- Wiley(Publisher)
Further investigations by Thomson, Rutherford, and Bohr refined this atomic model. The quantum mechanical model, even more recent, describes the behavior of electrons within the atom. • What is the structure of the atom? Thomson discovered that all atoms carry negatively charged electrons. Rutherford showed that atoms consist of a central, extremely small and highly dense, positively charged Summary 1 Atomic Structure 28 • How have we come to understand that matter is composed of atoms? Two ancient Greek philosophers, Aristotle and Democritus, proposed opposing theories of matter: Aristotle viewed matter as infinitely divisible, whereas Democritus conceived of matter as “atomistic.” Aristotle’s notion of matter dominated Western thought for two millennia. Then, in the early 1800s, Dalton Nitrogen 2.6% Calcium 1.4% All others 2% Oxygen 61% Carbon 23% Hydrogen 10% The most abundant elements of the human body (average percentage by mass) Summary 49 numbers. Deuterium and tritium, depicted here, are isotopes of hydrogen. The mass of an isotope can be estimated based on the number of protons and neutrons in its nucleus. • How do we determine the atomic mass of an element? The atomic mass of an element is the average of the masses of all the naturally occurring isotopes of that element, weighted for their individual abundances. 4 The Periodic Table 43 • How are elements organized in the periodic table? The periodic table, a portion of which is depicted here, consists of rows and columns of all known elements. As we move from left to right within each row, the sequential ele- ments within the row increase by one unit of atomic number. Each column consists of elements with similar chemical properties––except for hydrogen, which does not resemble any of the other elements in its column. nucleus, with (negatively charged) electrons orbiting around this nucleus.
eBook - PDFFundamentals of Materials Science and Engineering
An Integrated Approach
- William D. Callister, Jr., David G. Rethwisch(Authors)
- 2022(Publication Date)
- Wiley(Publisher)
3. (a) Schematically plot attractive, repulsive, and net energies versus interatomic separation for two atoms or ions. (b) Note on this plot the equilibrium separation and the bonding energy. 4. (a) Briefly describe ionic, covalent, metallic, hydrogen, and van der Waals bonds. (b) Note which materials exhibit each of these bonding types. Atomic Structure 2.2 | | FUNDAMENTAL CONCEPTS Some of the important properties of solid materials depend on geometric atomic arrangements and also the interactions that exist among constituent atoms or molecules. This chapter, by way of preparation for subsequent discussions, considers several fundamental and important concepts—namely, Atomic Structure, electron configurations in atoms and the periodic table, and the various types of primary and secondary inter- atomic bonds that hold together the atoms that compose a solid. These topics are reviewed briefly, under the assumption that some of the material is familiar to the reader. Each atom consists of a very small nucleus composed of protons and neutrons and is encircled by moving electrons. 1 Both electrons and protons are electrically charged, the charge magnitude being 1.602 × 10 −19 C, which is negative in sign for electrons and positive for protons; neutrons are electrically neutral. Masses for these subatomic particles are extremely small; protons and neutrons have approximately the same mass, 1.67 × 10 −27 kg, which is significantly larger than that of an electron, 9.11 × 10 −31 kg. 22 Chapter 2 Atomic Structure and Interatomic Bonding Each chemical element is characterized by the number of protons in the nucleus, or the atomic number (Z). 2 For an electrically neutral or complete atom, the atomic number also equals the number of electrons. This atomic number ranges in integral units from 1 for hydrogen to 92 for uranium, the highest of the naturally occurring elements.
eBook - PDFChemistry of the Non-Metals
With an Introduction to Atomic Structure and Chemical Bonding
- Ralf Steudel, Frederick C. Nachod, Jerry J. Zuckerman, Frederick C. Nachod, Jerry J. Zuckerman(Authors)
- 2011(Publication Date)
- De Gruyter(Publisher)
Part I: Atomic Structure and Chemical Bonding 1. Introduction Atoms are structured particles. This was first concluded from experiments on the conductivity of electrolytes and discharge through dilute gases which showed that electrons were a common constituent of all atoms. A further indication of the com-plex nature of heavier atoms came from the discovery of radioactivity by A. H. Be-querel (1896). P. Lenard discovered in 1903 that fast electrons can penetrate several layers of atoms in a metal foil without substantial change in direction. He concluded that atoms are not homogeneous spherical masses as had been assumed in the kinetic theory of gases, but rather that they are mostly empty space. Experiments by E. Rutherford, H. Geiger and E. Marsden (1906-1909) on the scattering of α-particles during the penetration of gold foils supported Lenard's conclusion. The mass of the atom must be concentrated in a very small region, since, while most α-particles went through the foil without scattering, some were scattered through large angles. Rutherford showed from the angular dependence of α-particle scattering that the atom had a small, massive nucleus of radius 10 ~ ! 2 cm, and he proposed a detailed model in 1911. The atom consists of a very small, positively-charged nucleus, representing most of the mass of the atom, which is surrounded by moving electrons. The movement of the electrons is determined by the equivalence of centrifugal and Coulombic attrac-tive forces. The numbers of nuclear charges and electrons are equal, insuring elec-tric neutrality. From the α-particle scattering, Rutherford calculated the nuclear charge number which agreed with the atomic number of the respective element in the periodic system proposed in 1869 by D.I. Mendeleev and independently by L. Meyer. The radii of atomic nuclei were calculated to be of the order of 5Ξ10 ~ 12 cm.
eBook - PDFThe History and Use of Our Earth's Chemical Elements
A Reference Guide
- Robert E. Krebs(Author)
- 2006(Publication Date)
- Greenwood(Publisher)
t w o Atomic Structure Early Ideas of Atomic Structure As mentioned in the previous section titled “A Short History of Chemistry,” many scien- tists identified elements, determined their characteristics, similarities, and differences, and designed symbols for them. Using unique experiments, scientists devised ways to define the structure of atoms and determine atomic weights, sizes, and electrical charges as well as energy levels for atoms. Many of these men and women recognized the existence of some order in the manner in which chemicals relate and react to each other. Although these scientists could not see the atoms themselves, they were aware that the structure of each element’s atoms has something to do with these characteristics. There were several attempts to organize the elements into a chart that reflected the particular nature of the atoms for these elements. Before the periodic table of the chemical elements was developed as we know it today, several relationships had to be established. (See the next section for more on the periodic table of the chemical elements.) The concept of electrons had been known for many years, but determining how these negatively charged particles react required experimentation and analysis of data. In about 1897, Joseph John Thomson (1856–1940) sent streams of electrons through magnetic fields, which resulted in the dispersion or spreading of the electrons. Thomson’s experiments, and those of others, led him to speculate that the atom was a positively charged “core” and that negatively charged particles of energy surrounded and matched the positive charge of this core or nucleus. Further, when these electrons were excited or “stirred up” with strong light, electricity, or mag- netism, some of them were driven from the outer regions of the atom. This was one of the first experimental evidences for the structure of the atom.
eBook - PDF- Morris Hein, Susan Arena, Cary Willard(Authors)
- 2016(Publication Date)
- Wiley(Publisher)
The properties of these three subatomic particles are summarized in TABLE 5.1. 5.4 • The Nuclear Atom 91 Nearly all the ordinary chemical properties of matter can be explained in terms of atoms consisting of electrons, protons, and neutrons. The discussion of Atomic Structure that fol- lows is based on the assumption that atoms contain only these principal subatomic particles. Many other subatomic particles, such as mesons, positrons, neutrinos, and antiprotons, have been discovered, but it is not yet clear whether all these particles are actually present in the atom or whether they are produced by reactions occurring within the nucleus. The fields of atomic and high-energy physics have produced a long list of subatomic particles. Descrip- tions of the properties of many of these particles are to be found in physics textbooks. ENHANCED EXAMPLE 5.3 The mass of a helium atom is 6.65 × 10 −24 g. How many atoms are in a 4.0-g sample of helium? SOLUTION (4.0 g ) ( 1 atom He 6.65 × 10 −24 g ) = 6.0 × 10 23 atoms He P R A C T I C E 5 . 3 The mass of an atom of hydrogen is 1.673 × 10 −24 g. How many atoms are in a 10.0-g sample of hydrogen? 5.4 The Nuclear Atom Explain how the nuclear model of the atom differs from Dalton’s and Thomson’s models. The discovery that positively charged particles are present in atoms came soon after the discovery of radioactivity by Henri Becquerel (1852–1908) in 1896. Radioactive elements spontaneously emit alpha particles, beta particles, and gamma rays from their nuclei (see Chapter 18). By 1907 Ernest Rutherford (1871–1937) had established that the positively charged alpha particles emitted by certain radioactive elements are ions of the element helium. Rutherford used these alpha particles to establish the nuclear nature of atoms. In experi- ments performed in 1911, he directed a stream of positively charged helium ions (alpha particles) at a very thin sheet of gold foil (about 1000 atoms thick).
eBook - PDFQuantum Chemistry
A Unified Approach
- David B Cook(Author)
- 2012(Publication Date)
- ICP(Publisher)
On the basis of this tiny amount of data 6 it is proposed to make the provisional assumption that: The atomic symbols in a conventional structural formula will be taken to mean the so-called ‘atomic cores’, that is, the atomic nucleus plus all those electrons which are not involved in any electron-sharing with other centres in the molecule. 7 This provisional definition will have to be revisited later, since it does not make the important distinction between the tightly-bound ‘inner’ electrons (the real cores) and any electrons in the ‘outer’ part of the atom which are not involved in chemical bonds (the lone pairs). Further, we may assume, again provisionally: The lines between atomic symbols in a structural diagram of a molecule each represent a pair of electrons which are shared between the two centres indicated by the atomic symbols. 6 The reader can, no doubt, supply all the additional data needed here! 7 This idea of ‘atomic cores’ will be used later to put the controversial idea of ‘oxi-dation number’ on a firm theoretical basis. Of course, the hydrogen atom has only one electron and its atomic core is just the nucleus. 50 What We Know About Atoms and Molecules And, finally, that: The separation of the electrons in a molecule 8 into ‘atomic cores’ and ‘bonds’ will provide the division we are seeking into the ‘environment-insensitive’ substructures which will enable their energies and distributions to be described, both qualitatively and quantitatively. What we need now is a method of approach to the description of the elec-tronic structures of these two types of molecular electronic substructure. 2.4 Assignment for Chapter 2 The familiar diagram which gives the energy levels available to electrons in the first 30 elements of the periodic table differs from the corresponding energy-level diagram for the hydrogen atom, since not all the levels for a given n have the same energy.
eBook - PDF- J.R. Nielsen(Author)
- 2013(Publication Date)
- North Holland(Publisher)
The common character of theories of atomic con- stitution has been the endeavour to find configura- tions and motions of the electrons which would seem to offer an interpretation of the variations of the chemical properties of the elements n+th the atomic number as they are so clearly exhibited in the well- known periodic law. A consideration of this law leads directly to the view that the electrons in the atom are arranged in distinctly separate groups, each containing a number of electrons equal to one of the periods in the sequence of the elements, arran ed according to increasing atomic number. In the frst attempts to obtain a definite picture of the configura- tion and motion of the electrons in these groups it was assumed that the electrons within each group at any moment were placed at equal angular intervals on a circular orbit with the nucleus at the centre, while in later theories this simple assumption has been replaced by thc assumptions that the configura- tions of electrons within the various groups do not possess such simple axial symmetry, hut exhibit a higher decree of symmetry in space, it nssumecl, for instance, that the configuratiobnPindi the electrons at anv moment during their motions possesew polyhedral symmetry. A11 such theories 3 iiivolvc, howevct, the fundaiiicntal difticulty that no interpretation is given why these configurations actually appear during the formation of the atom through a process of binding of the electrons by thc nucleus, and why the constitution of the atom is essentially stable in the sense that the original con- figuration is reorganised if it be tempor.arily dis- turbed by external agencies.
- Morris Hein, Scott Pattison, Susan Arena, Leo R. Best(Authors)
- 2014(Publication Date)
- Wiley(Publisher)
The mass of an atom therefore is primarily determined by the com- bined masses of its protons and neutrons. General Arrangement of Subatomic Particles The alpha-particle scattering experiments of Rutherford established that the atom contains a dense, positively charged nucleus. The later work of Chadwick demonstrated that the atom con- tains neutrons, which are particles with mass, but no charge. Rutherford also noted that light, negatively charged electrons are present and offset the positive charges in the nucleus. Based on this experimental evidence, a model of the atom and the location of its subatomic particles was devised in which each atom consists of a nucleus surrounded by electrons (see Figure 5.7). The nucleus contains protons and neutrons but does not contain electrons. In a neutral atom the posi- tive charge of the nucleus (due to protons) is exactly offset by the negative electrons. Because the charge of an electron is equal to, but of opposite sign than, the charge of a proton, a neutral atom must contain exactly the same number of electrons as protons. However, this model of Atomic Structure provides no information on the arrangement of electrons within the atom. Figure 5.7 In the nuclear model of the atom, protons and neutrons are located in the nucleus. The electrons are found in the remainder of the atom (which is mostly empty space because electrons are very tiny). Nucleus Electron region 10 –13 cm 10 –8 cm Proton Neutron A neutral atom contains the same number of protons and electrons. Source of alpha particles Beam of alpha particles Deflected particles Scattered alpha particles Most particles are undeflected Circular fluorescent screen Thin gold foil (a) (b) Figure 5.6 (a) Rutherford’s experiment on alpha-particle scattering, where positive alpha particles (a), emanating from a radioactive source, were directed at a thin gold foil.
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