6.2. Electron Configuration and the Periodic Table http://www.ck12.org
bromine is a dark orange liquid, and iodine is a dark purple-gray solid. Astatine is so rare that its properties are
mostly unknown.
Transition Elements
Transition elementsare the elements that are found in Groups 3-12 on the periodic table. The d sublevel, which
becomes increasingly filled from left to right across the period, is in a lower principal energy level than the s sublevel
filled before it. For example, the electron configuration of scandium, the first transition element, is [Ar]3d^1 4s^2.
Remember that the configuration is not written in the same order as the sublevels are filled; the 4s sublevel gets filled
before electrons are placed into 3d orbitals. Because they are all metals, the transition elements are often called the
transition metals (Figure6.7). As a group, they display typical metallic properties but are less reactive than the
metals in Groups 1 and 2. Some of the more familiar transition metals are unreactive enough to be found in nature
as pure elements, such as platinum, gold, and silver.
FIGURE 6.7
Silver (left) and chromium (right) are two
typical transition metals.Many transition elements make compounds that are distinctive for being vividly colored. Electron transitions that
occur within the d sublevel absorb some of the wavelengths present in white light, and the wavelengths that are not
absorbed are perceived by observers as the color of the compound (Figure6.8).
FIGURE 6.8
Transition metal compounds dissolved in
water exhibit a wide variety of bright col-
ors. From left to right are shown solutions
of cobalt(II) nitrate, potassium dichro-
mate, potassium chromate, nickel(II) chlo-
ride, copper(II) sulfate, and potassium
permanganate.The d-block
The transition elements found in Groups 3-12 are also referred to as the d-block, since the d sublevel is in the process
of being filled across the d-block from left to right. Since there are five d orbitals, each of which can accommodate