86 | The History and Use of Our Earth’s Chemical Elements Electronegativity is an important concept because the attractive force created by the posi-

86 | The History and Use of Our Earth’s Chemical Elements Electronegativity is an important concept because the attractive force created by the posi-

tive nuclei of atoms makes it possible for both the ionic and covalent bonding of atoms to form molecular compounds.

Many of the compounds formed by transition elements appear in various colors. Several are very toxic. Chromium, zinc, cobalt, nickel, and titanium are carcinogenic. There are several ways to present the transition elements. We present them as three series found in periods 4, 5, and 6. The first series starts at period 4, group 3 (IIIB) with the element scandium ( 21 Sc). The second series starts at period 5, group 3 (IIIB), with the element yttrium ( 39 Y). The third series starts at period 6, group 3 (IIIB) following a number of special metals. We start the third series

with the element hafnium ( 72 Hf).

Some authorities begin and end the transition elements at different groups in the periodic table. The transition elements sometimes continue beyond group 12 to include some metal- lic and semiconducting (metalloids) elements in groups 14, 15, and 16. These elements are presented in different sections.

We include transition elements in periods 4, 5, and 6 within groups 3 through 12 as sepa- rate sections.

Transition Elements: First Series—Period 4, Groups 3 to 12

SCANDIUM SYMBOL:฀Sc฀ PERIOD:฀4฀ GROUP:฀3฀(IIIB)฀ ATOMIC฀NO:฀21

ATOMIC฀MASS:฀44.956฀amu฀ VALENCE:฀2฀and฀3฀ OXIDATION฀STATE:฀+3฀ ฀ NATURAL฀STATE:฀Solid ORIGIN฀OF฀NAME:฀From฀the฀Latin฀word฀Scandia,฀for฀“Scandinavia.” ISOTOPES:฀There฀are฀28฀isotopes฀of฀scandium,฀ranging฀from฀scandium-36฀to฀scandium-57.฀

Scandium-45฀is฀the฀only฀stable฀isotope฀and฀contains฀about฀100%฀of฀the฀natural฀scan- dium฀found฀in฀the฀Earth’s฀crust.฀The฀remaining฀isotopes฀are฀radioactive฀with฀half-lives฀ ranging฀from฀nanoseconds฀to฀a฀few฀minutes฀to฀a฀few฀hours฀to฀a฀few฀days,฀and฀therefore,฀ they฀are฀not฀found฀naturally฀in฀the฀Earth’s฀crust.฀The฀radioactive฀isotopes฀of฀scandium฀ are฀produced฀in฀nuclear฀reactors.

ELECTRON฀CONFIGURATION ฀ Energy฀Levels/Shells/Electrons฀ Orbitals/Electrons

s2,฀p6

฀ 3-M฀=฀9฀

s2,฀p6,฀d1

฀ 4-N฀=฀2฀

s2

Guide to the Elements | 89 Properties

Scandium is a soft, lightweight, silvery-white metal that does not tarnish in air, but over time, it turns yellowish-pink. It resists corrosion. Scandium reacts vigorously with acids, but not water. Scandium has some properties similar to the rare-earth elements. Although its posi- tion in group 3 places it at the head of the 17 elements of the lanthanide series of rare-earth metals, scandium, as a metal, is not usually considered a rare-earth. Scandium’s melting point

is 1,541°C, its boiling point is 2836°C, and its density is 2.989 g/cm 3 .

Characteristics Scandium is the first element in the fourth period of the transition elements, which means

that the number of protons in their nuclei increases across the period. As with all the transi- tion elements, electrons in scandium are added to an incomplete inner shell rather than to the outer valence shell as with most other elements. This characteristic of using electrons in an inner shell results in the number of valence electrons being similar for these transition ele- ments although the transition elements may have different oxidation states. This is also why all the transition elements exhibit similar chemical activity.

Abundance฀and฀Source Although scandium is chemically similar to rare-earths, it no longer is considered to be one