This next section of the book, between pages 44 and 91, is devoted to the d-block elements, group by group. However, the elements with atomic numbers 104 to 112, which are part of the d-block, do not exist naturally, so they feature with the other transuranium elements, on pages 164–171. Further inspection of the periodic table highlights another irregularity: two elements in Group 3 are missing. In fact, they are part of a separate block of the periodic table: the f-block, which is explained on pages 92–3.
Understanding the d-block
There are two elements in Period 1 of the periodic table – hydrogen and helium – because there is
only one s-orbital available for electrons at energy level n=1 (each orbital can hold up to two electrons; see page 8). In each of Periods 2 and 3, there is an s-orbital and three p-orbitals – space for eight electrons, which is why Periods 2 and 3 have eight elements each.
But in Period 4, in addition to the s- and p-orbitals, another type of orbital becomes available: the d-orbital. There are five d-orbitals at each energy level, making room for an extra 10 electrons. This is why Periods 4 and 5 contain 18 elements each. The appearance of f-orbitals in Period 6 complicates this still further (see page 9).
The electrons in any given d-orbital actually have energies of the electrons in the period
How it Works Book of The Elements
44
D-block and the Transition Metals
Above: The elements of Groups 1 and 2 have their one or two outermost electrons in an s-orbital – that is why there are only
two columns at the le-hand end of the table. Those in the d-block have their outermost electrons in d-orbitals; as there are 5 d-orbitals, each with one or two electrons, this gives ten groups. The p-block contains elements in which the outermost electrons are in p-orbitals. There are three p-orbitals in each shell, producing a total of six columns (groups) in the p-block.
Opposite top: Shapes and relative orientations of the five p-orbitals.
d block s block p block f block 1 2 3 4 5 6 7
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WorldMags.net
WorldMags.net
below. So in Period 4, the electrons fill a 4s orbital and 4p orbitals but the d-orbitals are 3d, at energy level n=3. This is like stacking shelves from the floor up, but leaving one empty, only to be filled when you are halfway through filling the next one up. The electron configurations of d-block elements are normally written in a way to reflect this oddity: the lower-energy d-orbital is shown last, since it is filled last. So, for example, compare the electron configuration of s-block element calcium with d-block element vanadium, shown immediately to the right:
The transition metals
Because the d-block acts as a bridge, or transition, between the s- and p-blocks, the d-block elements are oen referred to as “transition metals”. A defined by IUPAC a transition metal is “an element whose atom has an incomplete d subshell, or which can give rise to cations (positive ions) with an incomplete d subshell”. This strict definition of what constitutes a transition metal rules out certain of the d-block elements. But in practice, the few elements that do not fit the definition are very similar to the “genuine” transition metals and they share the d-block, so they are normally included.
True to their name, the transition metals share properties common to all metals: they are shiny and silver-grey (exceptions being gold and copper), and they are good conductors of heat and electricity. They are malleable and ductile, meaning that they can be hammered or stretched, respectively, into different shapes – even mercury, a liquid at room temperature, is
malleable and ductile when solid. Transition metals are generally much less reactive than the Group 1 and 2 metals; some, such as gold, are even found in nature in their pure state. Most transition metals form a range of brightly coloured compounds, such as the famously bright blue copper sulfate, the redness of rubies caused by the presence of chromium ions, and the reddish-brown of the iron oxide in rust. And many transition metals are used as catalysts – agents that speed up a reaction but do not actually take part in the reaction. Transition metal catalysts are commonplace in industry, and also in complex biological reactions.
Transition metals mix well with each other, and as a result, they form a huge range of alloys (an alloy is a mixture that contains at least one metal). Steel is an alloy of the transition metal iron (Fe) with other elements; stainless steel, for example, includes another transition metal, chromium. The pages of this section feature some of these alloys, each finely tuned for particular applications.
d
z2z
z
z
z
z
y
y
y
y
y
x
x
x
x
x
d
x2-y2d
xyd
zxd
yzCalcium
1s
2Vanadium
2s
22p
63s
23p
64s
21s
22s
22p
63s
23p
64s
23d
3“Transition metals form a range
of brightly coloured compounds,
such as the famously bright blue
copper sulfate”
45
How it Works Book of The Elements
D-block and the Transition Metals
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WorldMags.net
Russian chemist Dmitri Mendeleev published the fi rst periodic table in 1869 (see page 21). Mendeleev le several gaps, which he correctly supposed were as-yet undiscovered elements. Scandium was assigned to one of those gaps, a er the element’s oxide was
discovered by Swedish chemist Lars Fredrik Nilson, in 1879. Since it was detected in a mineral found only in Scandinavia, Nilson called the new element scandium. It was not until 1937 that this elusive element was produced in its pure state.
Scandium is not particularly rare; its abundance in Earth’s crust is about the same as that of lead, and greater than tin’s. However, it is hardly ever found in high concentrations; it occurs instead as a trace element in over 800 diff erent minerals. Only a few tonnes of scandium are produced each year, most of it used to make strong, lightweight alloys with aluminium. Soviet missiles launched from submarines had nose cones made of scandium-aluminium alloy – strong enough to penetrate through polar sea ice but light enough not to add much weight.
Yttrium compounds have a variety of applications. Yttrium aluminium garnet (YAG) lasers are used in a wide variety of settings, including medical and dental procedures, surveying, cutting and digital communications. Yttrium oxide (Y2O3, yttria) added to zirconium oxide (ZrO2, zirconia) gives yttria-stabilized zirconia, a very stable and inert ceramic with a number of applications, including uses in oxygen sensors, heat-resistant elements in jet engines and industrial abrasives and bearings.
ATOMIC NUMBER: 21 ATOMIC RADIUS: 160 pm OXIDATION STATES: +1, +2, +3 ATOMIC WEIGHT: 44.96 MELTING POINT: 1,541ºC (2,806ºF) BOILING POINT: 2,836ºC (5,136ºF) DENSITY:2.99 g/cm3
ELECTRON CONFIGURATION: [Ar] 3d1 4s2
ATOMIC NUMBER: 39 ATOMIC RADIUS: 180 pm OXIDATION STATES: +1, +2, +3 ATOMIC WEIGHT: 88.91 MELTING POINT: 1,523ºC (2,774ºF) BOILING POINT: 3,337ºC (6,035ºF) DENSITY: 4.47 g/cm3 ELECTRON CONFIGURATION: [Kr] 4d1 5s2
Group 3 of the periodic table is made up of just two elements: scandium and yttrium. The two other spaces represent 16 elements each, comprising the 32 elements of the f-block. For more details, see pages 92–105.
Yttrium is o en considered to be a rare earth element (see page 94), because its properties and applications are very similar to those elements, and it is most o en found in the same mineral deposits as them. In fact, yttrium was the fi rst rare earth element to be discovered, by Finnish chemist Johan Gadolin. In 1787, Gadolin received a sample of a newly discovered mineral from a quarry in the Swedish village of Ytterby, and in that sample he identifi ed the oxide of the new element, in 1794. Yttrium was fi rst isolated in its elemental state by German chemist Friedrich Wöhler, in 1828.
21
Scandium
Sc
39
Yttrium
Y
Le : Sample of the rare earth metal yttrium, a rare earth element but,
as with scandium, not a lanthanoid.
Above right: Sample of pure scandium metal, a rare earth element
but not a lanthanoid.
“Soviet missiles launched
from submarines had nose
cones made of scandium-
aluminium alloy”
46
How it Works Book of The Elements