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.
8 Key excerpts on "Atomic Structure"
eBook - ePubChemistry
Concepts and Problems, A Self-Teaching Guide
- Richard Post, Chad Snyder, Clifford C. Houk(Authors)
- 2020(Publication Date)
- Jossey-Bass(Publisher)
...1 Atomic Structure, Periodic Table, Electronic Structure There is a smallest unit of substance. This smallest unit may be only a single atom or a group of atoms chemically joined together. This chapter deals with the structure of the atom, which is the very backbone of chemistry. In this chapter we introduce the three basic subatomic particles in an atom, their arrangement in the atom, and the similarities of this arrangement revealed by the position of the elements in the periodic table. A clear understanding of this chapter will give you a sound basis for learning chemistry. OBJECTIVES After completing this chapter, you will be able to define, describe, or illustrate: proton, neutron, electron, atom, nucleus, atomic number, shell, orbital, subshell, alkali metal, noble gas, halogen, alkaline earth, period, group, family, oxide, ductile, malleable, metal, nonmetal, metalloid, and Bohr model of an atom; determine the numbers of protons, neutrons, and electrons in a neutral atom when given its mass number and atomic number; compare and contrast the three fundamental particles in an atom according to mass and charge; determine the maximum number of electrons any given shell can hold; determine the maximum number of orbitals in any given shell; write the electron configuration for any element; determine what element is represented when given its electron configuration; use the periodic table to locate different families of elements and determine whether an element is a metal, nonmetal, or metalloid. An atom, the smallest unit of an element, is composed primarily of three fundamental particles: electrons, protons, and neutrons. The combination of these particles in an atom is distinct for each element. An atom of the element radon is composed primarily of a specific combination of what three basic particles?_____________ Answer: electrons, protons, neutrons (any order) Let's forget about neutrons for the moment and consider just electrons and protons...
eBook - ePub- Tony Cox(Author)
- 2004(Publication Date)
- Taylor & Francis(Publisher)
...A1 T HE NUCLEAR ATOM Key Notes Electrons and nuclei An atom consists of a very small positively charged nucleus, surrounded by negative electrons held by electrostatic attraction. The motion of electrons changes when chemical bonds are formed, nuclei being unaltered. Nuclear structure Nuclei contain positive protons and uncharged neutrons. The number of protons is the atomic number (Z) of an element. The attractive strong interaction between protons and neutrons is opposed by electrostatic repulsion between protons. Repulsion dominates as Z increases and there is only a limited number of stable elements. Isotopes Isotopes are atoms with the same atomic number but different numbers of neutrons. Many elements consist naturally of mixtures of isotopes, with very similar chemical properties. Radioactivity Unstable nuclei decompose by emitting high-energy particles. All elements with Z > 83 are radioactive. The Earth contains some long-lived radioactive elements and smaller amount of short-lived ones. Related topics Actinium and the actinides (I2) Origin and abundance of the elements (J1) Electrons and nuclei The familiar planetary model of the atom was proposed by Rutherford in 1912 following experiments by Geiger and Marsden showing that nearly all the mass of an atom was concentrated in a positively charged nucleus. Negatively charged electrons are attracted to the nucleus by the electrostatic force and were considered by Rutherford to ‘orbit’ it in a similar way to the planets round the Sun. It was soon realized that a proper description of atoms required the quantum theory; although the planetary model remains a useful analogy from the macroscopic world, many of the physical ideas that work for familiar objects must be abandoned or modified at the microscopic atomic level. The lightest atomic nucleus (that of hydrogen) is 1830 times more massive than an electron...
eBook - ePub- Suzanne Easton(Author)
- 2012(Publication Date)
- Wiley-Blackwell(Publisher)
...definitions of an atom, element and other related terms are given in Table 3.1. The ‘Make-Up’ of an atom – Atomic Structure The atom is the basic unit involved in the production and use of X-rays. Unless a vacuum has been created, atoms are present in every solid, liquid and gas. The atomic nucleus Atoms are composed of a nucleus that contains protons and neutrons. Protons are positively charged. Neutrons have no electrical charge. Neutrons and protons together are termed nucleons. Electrons surround the nucleus of an atom (Figure 3.1). Figure 3.1 The structure of an atom. Protons and neutrons are about 2000 times bigger than electrons. For this reason, the mass of an atom is almost completely made up of the protons and neutrons in its nucleus. The total number of protons and neutrons in the nucleus is known as the mass number. Forces known as short-range forces hold the nucleus together. These are very strong forces. The energy used in keeping the nucleus together is called binding energy. If the nucleus was scaled to match the centre spot of a football pitch, the electron shells would start at the perimeter of the pitch and the outer orbits would be found several miles beyond this. Shells and energy The electrons orbit around the nucleus in different planes; these planes are called shells. The shells are called K, L, M, N, O and P. Normally, the number of electrons orbiting the nucleus equals the number of protons found in the nucleus (Table 3.2). The shells nearest the nucleus will always be the first to be completely filled. This is because they have lower energy levels and are easier to fill. 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...
eBook - ePub- Jeffrey Gaffney, Nancy Marley(Authors)
- 2017(Publication Date)
- Elsevier(Publisher)
...It was determined that atoms are made up of three types of particles: electrons, protons, and neutrons. The atomic nucleus consists of positively charged protons and uncharged neutrons held tightly together in a small volume at the center of the atom as shown in Fig. 2.1. The negatively charged electrons “orbit” this nucleus forming the electron cloud surrounding the nucleus. Since the proton and neutron have the highest mass of the three particles (see Table 2.1), the nucleus makes up most of the mass of the atom while the electrons in their orbits make up most of the volume of the atom. Fig. 2.1 Structure of the atom. Table 2.1 Properties of the Subatomic Particles Particle Symbol Charge Mass (g) Mass Relative to Neutron Proton p + 1 1.6726 × 10 − 24 0.9986 Neutron n 0 1.6749 × 10 − 24 1.0 Electron e − − 1 9.1094 × 10 − 28 0.0005439 The number of protons in the nucleus of the atom is the atomic number of the element and is commonly designated by the symbol Z. For a neutral atom, the number of electrons equals the number of protons. The atomic number is specific to each element as it also determines the number of electrons, which determines the properties of the element. The sum of the number of protons and neutrons in the nucleus is called the mass number of the element since these two heaviest particles determine the approximate mass of the atom. The mass number is commonly designated by the symbol A. • Z = number of protons = number of electrons • A = number of protons + number of neutrons • A – Z = number of neutrons An atomic symbol is used to abbreviate the Atomic Structures of each element as; where X is the symbol of the element as listed in Table 2.2, Z is the atomic number of the element, and A is the mass number. The use of the atomic number (Z) in the atomic symbol is optional since the number of protons is specific to an element and can be obtained from the element symbol itself...
- Mark Kernion, Joseph A. Mascetta(Authors)
- 2021(Publication Date)
- Barrons Educational Services(Publisher)
...PART II THE NATURE OF MATTER 2 Atomic Structure AND THE PERIODIC TABLE WHAT YOU WILL LEARN Upon completing this chapter, you will be able to: • Describe the history of the development of atomic theory • Explain the structure of atoms • Understand and predict the placement of electrons in principal energy levels and sublevels and the subsequent notation for such placement • Place atoms in groups and periods based on their structure in the periodic table • Explain how chemical and physical properties are related to position in the periodic table History The idea of small, invisible particles being the building blocks of matter can be traced back more than 2000 years to the Greek philosophers Democritus and Leucippus. These particles were supposed to be so small and indestructible that they could not be divided into smaller particles. The Greek word for “indivisible” is atmos. The English word atom comes from this Greek word. This early concept of atoms was not based upon experimental evidence but was simply a result of thinking and reasoning on the part of the philosophers. It was not until the eighteenth century that experimental evidence in favor of the atomic hypothesis began to accumulate. Finally, about 1805, John Dalton proposed some basic assumptions about atoms based on what was known through scientific experimentation and observation at that time. These assumptions were very closely related to what we presently know about atoms. Because of this, Dalton is often referred to as the father of modern atomic theory...
- 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- Kevin R. Reel(Author)
- 2013(Publication Date)
- Research & Education Association(Publisher)
...CHAPTER 2 The Structure of Matter CHAPTER 2 THE STRUCTURE OF MATTER ATOMIC THEORY AND STRUCTURE EVIDENCE FOR ATOMIC THEORY Dalton • John Dalton performed chemical reactions and carefully measured the masses of reactants and products. • Dalton proposed that all matter is composed of subunits call atoms. Atoms had different identities, called elements. Elements combined together in definite ratios to form compounds. • Atoms are never created or destroyed during chemical reactions. Thompson • J. J. Thompson observed the deflection of particles in a cathode ray tube. • He concluded that atoms are composed of positive and negative charges. • He called negative charges electrons, and he suggested that the positive charges were distributed in islands throughout the atom, like raisins in raisin bread. Some people at the time called this the “plum pudding” model of the atom. Millikan • Robert Millikan used oil drops falling in an electric field of known strength to calculate the charge-to-mass ratio of electrons and to surmise the charge contained by a single electron. Rutherford • Ernest Rutherford fired alpha particles (that he knew to be positively charged) through thin, gold foil. • Rutherford measured the resulting scatter patterns of the alpha particles after they hit the foil. He found that most of the alpha particles moved right through the foil, or were deflected slightly. However, some alpha particles were deflected at large angles, as though they had collided with a heavier object and bounced back. • He concluded that the positive charge and the mass of the atom are concentrated at the center of the atom, and that the rest of the atom is mostly empty space...
eBook - ePub- Dov M. Gabbay, Paul Thagard, John Woods, Dov M. Gabbay, Paul Thagard, John Woods(Authors)
- 2011(Publication Date)
- North Holland(Publisher)
...Hence he concludes ArCl 2 is a unified whole, “a new chemical entity,” which can properly be said to exist, if only briefly. 20. One Set of Nuclei and Electrons Any theory of molecular structure must be consistent with quantum mechanics. But should every true story about molecules follow from quantum mechanics? The non-reduction of molecular chemistry has often been argued for by pointing out that quantum chemistry borrows the notion of molecular structure from classical chemistry (see the article on ‘Atoms and Molecules in Classical Chemistry and Quantum Mechanics’ in Part 5 of this Volume). 120 In quantum theory an atom or molecule has no extension in space or time; neither electrons nor nuclei exist as individual objects; electrons are indistinguishable, not identifiable or localizable entities. In particular, chirality has been pointed out as something not found in quantum mechanics, but any form of asymmetry seems to be problematic. 120 A complete Hamiltonian would have to include, at least, all nuclear and electronic kinetic energy operators, electrostatic interactions between all charged particles, and interactions for all magnetic moments due to spin and orbital motions of nuclei and electrons. In making the choice what terms to include, information is used that is not provided by quantum mechanics. There seems to be some sort of consensus that structure arises or may arise, because of interactions with the environment, variously referred to in terms of “symmetry breaking”, “suppressing EPR-correlations”, “decoherence,” etc. Another way of putting this is saying that contexts are at least as important as first principles; the latter being necessary conditions, not sufficient conditions...
