Sodium atomic radii

Only body-centered cubic crystals, lattice constant 428.2 pm at 20°C, are reported for sodium (4). The atomic radius is 185 pm, the ionic radius 97 pm, and electronic configuration is lE2E2 3T (5). Physical properties of sodium are given ia Table 2. Greater detail and other properties are also available... 

Ions, like atoms, have size. For ions, the term is ionic radii. For cations, the loss of electrons results in a decrease in size, since (for the representative metals) an entire energy level is usually lost. A sodium ion, Na+, is smaller than a sodium atom. The greater the number of electrons removed, the greater the decrease in radius. This applies to any element and its cations as illustrated by the trend in radii of Fe > Fe2+ > Fe3+. 

Sodium has a density of 0.971 g/cm3 and crystallizes with a body-centered cubic unit cell. What is the radius of a sodium atom, and what is the edge length of the cell (both in picometers) ... 

To obtain a picture of how loosely the valence electron in an alkali metal is held, consider two quantities connected with the most common of the alkali metals, sodium, the atomic radius arid the ionic radius. Now, one must be careful in speaking of the sizes of atoms or ions just as... 

For metals such as sodium, the atomic radius is defined as half the distance between adjacent nuclei in a crystal of the element. See Figure 6-11a. For elements that commonly occur as molecules, such as many nonmetals, the... 

When atoms lose electrons and form positively charged ions, they always become smaller. For example, as shown in Figure 6-13a on the next page a sodium atom with a radius of 186 pm shrinks to a radius of 95 pm when it forms a positive sodium ion. The reason for the decrease in size is twofold. The electron lost from the atom will always be a valence electron. The loss of a valence electron may leave a completely empty outer orbital, which results in a smaller radius. Furthermore, the electrostatic repulsion between the now fewer number of remaining electrons decreases, allowing them to be pulled closer to the nucleus. 

It is seen that the atomic radius for sodium is almost the double of that of chlorine. When you move down a group (vertically down) the atomic radius increases which is sketched in Figure 1 - 10 for the elements in the 1 main group. 

Sodium, with a covalent radius of 157 pm, can occupy all the available voids of both structures, but the type II host lattice is the more stable. Experimental data agree with this argument type I clathrates are formed in milder conditions than type II. This type II structure formed with small sodium atoms is unique and has no hydrate equivalent both voids are occupied stoichiometrically and a large range of composition is observed 3 < x < 22. 

Due to the loss of valence electrons, positive ions are smaller than the metal atoms from which they are formed. The sodium atom has a radius of 0.186 nm while the sodium ion has a radius of 0.095 nm. The difference in radii between atom and cation is due to the excess of protons in the ion, which draws the outer electrons closer to the nucleus (Masterton et al. 1986). 

Which has the largest atomic radius magnesium (Mg), silicon (Si), sulfur (S), or sodium (Na) The smallest ... 

Figure 6.13a illustrates how the radius of sodium decreases when sodium atoms form positive ions, and Figure 6.13b shows how the radius of chlorine increases when chlorine atoms form negative ions. 

I) Explain why the radius of a sodium atom Is larger than that of a sodium Ion, whereas that of a chlorine atom is sma//er than a chloride Ion. 

Sodium metal (atomic weight 22.99 g/cm ) adopts a body-centered cubic structure with a density of 0.97g/cm (a) Use this information and Avogadro s number (Na = 6.022 X 10 ) to estimate the atomic radius of sodium, (b) If it didn t react so vigorously, sodium could float on water. Use the answer from part (a) to estimate the density of Na if its structure were that of a cubic close-packed metaL Would it still float on water ... 

Elemental cesium reacts more violently with water than does elemental sodium. Which of the following best explains this difference in reactivity (i) Sodium has greater metallic character than does cesium, (ii) The first ionization energy of cesium is less than that of sodium, (iii) The electron affinity of sodium is smaller than that of cesium, (iv) The effective nuclear charge for cesium is less than that of sodium, (v) The atomic radius of cesium is smaller than that of sodium. 

All the above results are consistent with a rather high probability of the presence of 3 s electrons on the sodium atoms, although they contribute to the density of states at the bottom of the conduction band of silicon atoms, for which the NMR resonance lines are also notably shifted. They are in agreement with the conclusions of the qualitative comparison between the free radii of the cages and the effective radius of sodium atoms in clathrates (Fig. 1.4 in Sect. 1.7). 

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