Elements atomic radii

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. ...

Within a family (vertical group on the periodic table) of representative elements, atomic radii increase from top to bottom as electrons are added to shells farther from the nucleus. 

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.)...

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. 

Atomic number Element Atomic radius (s) Radius oj M ion (nm) Ionisation energies (kJ mol I 1st 2nd 3rd ... 

Element Atom radius, pm Effective ionic radii, pm ... 

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. 

Element Atomic Radius (A) Ionic Radius (A) (4- coordination) Electro- negativity Polarizing Power (charge/radius2)... 

Symbol Sb atomic number 51 atomic weight 121.75 Group VA (group 15) element atomic radius 1.41A ionic radius 86 + 0.76A covalent radius 1.21A electronic configuration [Kr] 4di°5s25p3 a metalloid element electronegativity 1.82 (Allred-Rochow type) valence states +5, +3, 0 and -3 isotopes and natural abundance Sb-121 (57.3%), Sb-123 (42.7%)... 

Symbol Be atomic number 4 atomic weight 9.012 a Group IIA (Group 2) metal the lightest alkaline-earth metallic element atomic radius l.OOA ionic radius (Be2+) 0.30A electronic configuration Is22s2 ionization potential, Be 9.32eV, Be + 18.21 eV oxidation state +2... 

Symbol Hf atomic number 72 atomic weight 178.49 a Group IV B (Group 4) transition metal element atomic radius 1.442A electron configuration [Xe]4/i45d26s2 common valence +4, also exhibits oxidation states +2 and -i-3 most abundant natural isotope Hf-180 isotopes and their natural abundances Hf-176 (5.21%), Hf-177 (18.56%), Hf-178 (27.10%), Hf-179 (13.75%), Hf-180 (35.22%), artificial isotopes 157, 158, 168, 173, 175, 181-183. 

Name of element Atomic radius in picometres (pm) Name of element Atomic radius in picometres (pm) Name of element Atomic radius in picometres (pm)... 

Element Atomic Radius (A) Element Atomic Radius (A)... 

Element Atomic radius Ionic radius Element Atomic radius Ionic radius... 

Relative atomic radii for the representative elements. Atomic radius decreases across a period and increases down a group in the periodic table. 

Figure 22.3 Trends in key atomic properties of Period 4 elements. Atomic radius (A), electronegativity (B), and first ionization energy (C) of all Period 4 elements are shown as heights of posts, with darker shading for the transition series.

Group 17 element Atomic radius / nm Melting point / °C Boiling point/°C Colour... 

Element Atomic Radius (nm) Crystal Structure Electro- negativity Valence... 

The data in Table 7.1 show that, as expected, density, ionic radius, and atomic radius increase with increasing atomic number. However, we should also note the marked differences in m.p. and liquid range of boron compared with the other Group III elements here we have the first indication of the very large difference in properties between boron and the other elements in the group. Boron is in fact a non-metal, whilst the remaining elements are metals with closely related properties. 

Element Atomic number Outer electrons Atomic radius (nm) m.p. (K) h.p. (K) 1st ionisation energy (kj Electro- negativity (Pauling)... 

The atom radius of an element is the shortest distance between like atoms. It is the distance of the centers of the atoms from one another in metallic crystals and for these materials the atom radius is often called the metal radius. Except for the lanthanides (CN = 6), CN = 12 for the elements. The atom radii listed in Table 4.6 are taken mostly from A. Kelly and G. W. Groves, Crystallography and Crystal Defects, Addison-Wesley, Reading, Mass., 1970. 

The most common oxidation state of niobium is +5, although many anhydrous compounds have been made with lower oxidation states, notably +4 and +3, and Nb can be reduced in aqueous solution to Nb by zinc. The aqueous chemistry primarily involves halo- and organic acid anionic complexes. Virtually no cationic chemistry exists because of the irreversible hydrolysis of the cation in dilute solutions. Metal—metal bonding is common. Extensive polymeric anions form. Niobium resembles tantalum and titanium in its chemistry, and separation from these elements is difficult. In the soHd state, niobium has the same atomic radius as tantalum and essentially the same ionic radius as well, ie, Nb Ta = 68 pm. This is the same size as Ti ... 

The atomic radius of silver (144 pm) is within about 15% of many elements, permitting sofid solutions with Al, Au, Be, Bi, Cu, Cd, Ge, In, Mn, Pb, Pd, Pt, Sb, Sn, Th, and Zn. These metals form useful braziag, jewelry, and soldering alloys. Copper is the only metal with which silver forms a simple eutectic between two sofid solutions (Pig. 3). Silver has extremely limited solubiUtyia B, C, Co, Cr, Pe, Ge, Ir, Ni, Mg, Mo, Se, Si, Te, Ti, and W. Thus these metals may be brazed by silver alloys without serious erosion during welding (qv). 

Some metals are soluble as atomic species in molten silicates, the most quantitative studies having been made with Ca0-Si02-Al203(37, 26, 27 mole per cent respectively). The results at 1800 K gave solubilities of 0.055, 0.16, 0.001 and 0.101 for the pure metals Cu, Ag, Au and Pb. When these metal solubilities were compared for metal alloys which produced 1 mm Hg pressure of each of these elements at this temperature, it was found drat the solubility decreases as the atomic radius increases, i.e. when die difference in vapour pressure of die pure metals is removed by alloy formation. If the solution was subjected to a temperature cycle of about 20 K around the control temperamre, the copper solution precipitated copper particles which grew with time. Thus the liquid metal drops, once precipitated, remained stable thereafter. 

The electron configuration or orbital diagram of an atom of an element can be deduced from its position in the periodic table. Beyond that, position in the table can be used to predict (Section 6.8) the relative sizes of atoms and ions (atomic radius, ionic radius) and the relative tendencies of atoms to give up or acquire electrons (ionization energy, electronegativity). 

Atomic radii. The radii are determined by assuming that atoms in closest contact in an element touch one another. The atomic radius is taken to be one half of the closest internuclear distance, (a) Arrangement of copper atoms in metallic copper, giving an atomic radius of 0.128 nm for copper, (b) Chlorine atoms in a chlorine (Cl2) molecule, giving an atomic radius of 0.099 nm for chlorine. 

Strictly speaking, the size of an atom is a rather nebulous concept The electron cloud surrounding the nucleus does not have a sharp boundary. However, a quantity called the atomic radius can be defined and measured, assuming a spherical atom. Ordinarily, the atomic radius is taken to be one half the distance of closest approach between atoms in an elemental substance (Figure 6.12). 

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