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The programme is in two parts : In the first Dr. Harding explains how the electron may be described in terms of a wave function. Using this description a picture is built of the electron distributi...on in a hydrogen atom. This is then extended to the hydrogen molecule as the Molecular Orbital approach to bonding. In the second half Dr. Mason explains one way of measuring the size of the elements in compounds, by means of their covalent radii. Comparison of covalent radii shows two trends, they get smaller across the rows even though the elements get heavier, and down the periods the size increases. Dr. Mason describes how this may be explained in terms of effective nuclear charge. Prof. Haynes ends the programme by pointing out some of the areas of chemistry in which the size of the elements play an important role.
Metadata describing this Open University video programme
Item code: S25-; 08
First transmission date: 06-05-1972
Published: 1972
Rights Statement:
Restrictions on use:
Duration: 00:24:22
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Producer: Barrie Whatley
Contributors: Charlews Harding; Len Haynes; Joan Mason
Publisher: BBC Open University
Keyword(s): Covalent radii; Effective nuclear discharge; Electrons; Hydrogen atom; Hydrogen molecule; Rows and periods; Size of elements; Wave function
Footage description: Len Haynes introduces the programme. Charlie Harding looks at two alternative models for the shape of atoms. He goes on to explain how an atom's electrons may be described in terms of wave functions. Graphs are shown to illustrate these functions. Harding discusses the mathematics for determining the radial distribution - the probability of the electron being at any one place on the electron shell. An animated diagram shows two hydrogen atoms approaching each other. Harding, with the aid of further diagrams, explains how the molecular wave function at this equilibrium bond distance is obtained. He shows that in the formation of a hydrogen molecule, there is an increase in electron density between the two nuclei which holds the molecule together. Joan Mason discusses the size of atoms and methods for measuring their size. She begins with atoms in the second row of the periodic table. Diagrams aid the discussion. She notes that as the atoms in the row become heavier, they become smaller. Mason with the aid of a diagram explains how the size of a bonded solid chlorine atom is calculated. Joan Mason shows that covalent bond length between two like atoms is roughly constant for different compounds. She then shows that the covalent bond length between two unlike atoms is also roughly constant in different molecules. Mason notes that one must specify single covelent bonds to define bond length. Shots of a chart- showing bond lengths for second and third row atoms. The rest of Group 1 is now shown on the chart. Mason points out that size increases down the group but decreases across each row. Joan Mason discusses other atomic properties which display similar trends such as ionization energy of electrons. Shot of a graph showing ionization energy of electrons. Mason goes on to discuss the way in which electrons in atoms change across the periodic table. She explains the use of the Coulomb Law, which gives the force holding the valence electrons in simple atoms like hydrogen. She also explains how the nuclear charge for the more complex atoms is determined. Several diagrams and diffraction photographs aid the discussion. Joan Mason goes back to the second row atoms and sums up the reasons for their exceptional small size. Mason next considers what happens to the size of atoms when they form ions. She uses hydrogen as her first example. Mason then looks at several other atoms. Len Haynes concludes with some comments on the significance of atomic size and ionization energy. He points out areas of chemistry in which these play important roles. Haynes uses a large periodic table to aid his discussion.
Master spool number: 6LT/70492
Production number: 00521_3122
Videofinder number: 1776
Available to public: no