Atomic radius main-group elements

Figure 1.3. Atomic radii of the main-group elements. Atomic radii increase as one goes down a group and in general decrease going across a row in the Periodic Table. Hydrogen has the smallest atom and cesium the largest. ...

For main-group elements, atomic radii deaease aaoss a period because the addition of a proton in the nucleus and an electron in the outermost energy level inaeases Zgff. This does not happen in the transition metals because the electrons are added to the highest-1 orbital and the Zeff stays roughly the same. 

Figure 8.9 Atomic radii of the main-group and transition elements. Atomic radii (in picometers) are shown as haif-spheres of proportionai size for the main-group eiements (fan) and the transition eiements (blue). Among the main-group elements, atomic radius generally increases from top to bottom and decreases from left to right. The transition elements do not exhibit these trends as consistently. (Values in parentheses have only two significant figures values for the noble gases are based on quantum-mechanical calculations.)...

The radii of cations and anions derived from atoms of the main-group elements are shown at the bottom of Figure 6.13. The trends referred to previously for atomic radii are dearly visible with ionic radius as well. Notice, for example, that ionic radius increases moving down a group in the periodic table. Moreover the radii of both cations (left) and anions (right) decrease from left to right across a period. 

All the elements in a main group have in common a characteristic valence electron configuration. The electron configuration controls the valence of the element (the number of bonds that it can form) and affects its chemical and physical properties. Five atomic properties are principally responsible for the characteristic properties of each element atomic radius, ionization energy, electron affinity, electronegativity, and polarizability. All five properties are related to trends in the effective nuclear charge experienced by the valence electrons and their distance from the nucleus. 

The table below lists the atomic radii (plural of radius) for the main-group elements. Design different scale models that could help you visualize and compare the sizes of the atoms. Your models can be two-dimensional or three-dimensional, large or small. 

Would you expect atoms of the transition elements to follow the same trend you observed for the main-group elements Locate atomic radius data for the transition elements (not including the inner transition elements). Make additional models, or draw line or bar graphs, to verify your expectations. 

Atomic radius is approximately the distance from the nucleus of an atom to the outside of the electron cloud where the valence electrons are formd. The reactivity of the -atom depends on how easily the valence electrons can be removed, and that depends on their distance from the attractive force of the nucleus. In this MiniLab, you will study the periodic trends in the atomic radii of the first 36 main group elements from hydrogen through barimn. 

Obtain a 96-weU microplate, straws of a size to fit the wells in the plate, scissors, and a ruler. The well plate should be oriented to correlate with the periodic table of the elements in the following way Row 1 of the plate represents the first period, HI as hydrogen, A1 as helium Row 2 of the plate represents the second period, from H2 (lithium) to A2 (neon). Rows 3 to 7 correlate with Periods 3 to 7 however, only the main group elements will be represented. Label the well plate Atomic radius in pm (picometers). 

Figure 1-10 Relative atomic radius for 1 main group elements...

Across a period, eff dominates. As we move across a period of main-group elements, electrons are added to the same outer level, so the shielding by inner electrons does not change. Because outer electrons shield each other poorly, Zeff on the outer electrons rises significantly, and so they are pulled closer to the nucleus. Atomic radius generally decreases in a period from left to right. 

Figure 22.3 Horizontal trends in key atomic properties of the Period 4 elements. The atomic radius (A), electronegativity (B), and first ionization energy (C) of the elements in Period 4 are shown as posts of different heights, with darker shades for the transition series. The transition elements exhibit smaller, less regular changes for these properties than do the main-group elements.

Ionic radius data from R. D. Shannon, Acta Crystallogr. 1976, A32, 751. Note how the ionic radii are smaller than the covalent radii the ionic radii are most suitable for bonds where the electronegativity difference between the constituent atoms is large (see Scheme 8.1). These radii should be combined with ionic radii for main group elements to predict bond distances. 

Figure 7.6 shows the atomic radii of the main group elements according to their positions in the periodic table. There are two distinct trends. The atomic radius decreases as we move from left to right across a period and increases from top to bottom as we move down within a group. 

When an atom loses an electron and becomes a cation, its radius decreases due in part to a reduction in electron-electron repulsions (and con.sequently a i uction in shielding) in the valence shell. A significant decrease in radius occurs when all of an atom s valence electrons are removed. This is the case with ions of most main group elements, which are isoelectronic with the noble gases preceding them. Consider Na. which loses its 3s electron to become Na ... 

Figure 7.12 shows the ionic radii for those ions of main group elements that are isoelectronic with noble gases and compares them to the radii of the parent atoms. Note that the ionic radius, like the atomic radius, increases from top to bottom in a group. 

Figure 8.9 shows the atomic radius plotted as a function of atomic number for the first 57 elements in the periodic table. Notice the periodic trend in the radii. Atonfic radii peak with each alkali metal. Figure 8.10 is a relief map of atomic radii for most of the elements in the periodic table. The general trends in the atomic radii of main-group elements, which are the same as trends observed in van der Waals radii, are ... 

Define atomic radius. For main-group elements, give the observed trends in atomic radius as you... 

Explain why atomic radius decreases as we move to the right across a period for main-group elements but not for transition elements. 

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