Metals Denser Than Lead at Room Temperature Pt 2 Quiz

Answer:

Here are the metallic elements denser than lead at room temperature:

Berkelium (Bk) is often cited as being 14.78 grams per cubic centimeter at room temperature. Like other actinides (15 radioactive metallic chemical elements located in the bottom row of the periodic table) berkelium (atomic number 97) is also synthetic, and typically exists only in trace amounts in laboratories. Its density is based on measurements from very small samples.

Curium (Cm), density: 13.51 g/cc (for the most stable isotope, Cm-244). Curium is a radioactive actinide metal, typically synthesized in nuclear reactors. While it's not common outside specialized research or nuclear interests, its physical properties (like density) are well-studied. It was first produced in 1944 and does not exist in nature in meaningful quantities. It is primarily used in research and as a power source in radioisotope thermoelectric generators for space probes.

Hafnium (Hf), density: 13.31 g/cc. About 17% denser than the famously heavy and dense lead, Hafnium is a transition metal, chemically similar to zirconium. It is used in control rods for nuclear reactors due to its high neutron absorption cross-section. Hafnium is denser than lead not because its atoms are heavier, but because of the "Lanthanide Contraction" in which certain metal atoms in the lanthanide series get a little smaller than you would expect as you go across the row in the periodic table from lanthanum to lutetium. The atoms get "squeezed" into a much smaller volume, resulting in them getting packed together more tightly.

Mercury (Hg), density: 13.5 g/cc. Mercury is the only metal that is liquid at room temperature, which makes it even more surprising that it should be denser than lead. Being a liquid does not mean "less dense"; it only means the atoms don't lock into a rigid structure. Mercury's electron arrangement makes the bonds between atoms weak enough that it stays liquid at room temperature, unlike most other very dense metals. Mercury is still used in some thermometers, but not so much in fluorescent lamps anymore since it can evaporate at room temperature and become a toxic vapor, making exposure risky for humans and wildlife. Safer alternatives such as digital thermometers and LED lighting have been recommended.

Neptunium (Np), density: 20.5 g/cc. Primarily a byproduct of nuclear reactors, neptunium is radioactive and is almost twice as dense as lead at room temperature. A cubic inch of neptunium would weigh over 1 pound, or around 470 grams. Its high density means small samples have noticeable "heft"-scientists describe actinide metals as "feeling like a solid lump of gravity."

Platinum (Pt), density: 21.5 g/cc. The precious metal platinum is used in catalytic converters, laboratory equipment, and jewelry. Since density measures mass per unit volume, platinum is denser than lead because its atoms are heavier: platinum's atomic mass of 195 vs. lead's 207, but platinum has a tighter atomic packing. Platinum's crystal structure (face-centered cubic) packs atoms closer together than lead's looser arrangement.

Protactinium (Pa), density: 15.4, g/cc. Thirty-three % denser than lead, protactinium is a rare, radioactive, and highly toxic element with no major commercial applications. Protactinium's heavier atoms along with the compacting effect of the lanthanide contraction makes for the element's high density, even with a crystal structure that isn't typically the most efficient for packing.

Ruthenium (Ru), density: 12.1, g/cc. One of the Platinum Group metals (all of which are denser than lead) ruthenium is used to harden alloys and as in electrical contacts. Even though a ruthenium atom is half the mass of a lead atom (atomic mass of 101.07 u compared to lead's 207.2 u), its vastly smaller size means that nearly twice as many ruthenium atoms can fit into the same volume.

Thallium (Tl), density: 11.8, g/cc. Thallium and lead are very close in density, but thallium is slightly denser due to the interplay between atomic mass, atomic size, and most importantly, crystal structure. Thallium is highly toxic and is used in specialized electronics and glass manufacturing.

Tungsten (W), density: 19.3, g/cc. Tungsten has the highest melting point of all the elements, and is used in lamp filaments, weights, and armor-piercing rounds of ammunition. It has very strong metallic bonds, so its atoms are tightly packed with high electron density. Tungsten has very heavy atoms (atomic mass 183.84 u) that are crammed into a very small volume by the lanthanide contraction. This combination is so strong that it easily overcomes tungsten's less efficient packing of its BCC (Body-Centered Cubic) crystal structure, making it nearly twice as dense as lead.

Uranium (U), density: 19.1, g/cc. Uranium is radioactive, being the primary fuel for nuclear power generation. Uranium's greater density than lead is driven almost entirely by the extreme mass of its atoms-atomic mass of 238.03 u compared to lead's 207.2 u). Even though its orthorhombic crystal structure doesn't pack atoms as efficiently as lead's FCC (Face-Centered Cubic) structure, in which atoms are located at each of the eight corners of a cube and at the center of each of the six cube faces. The orthorhombic structure is when the length, width, and height are all different measurements, but all the corners are perfect right angles, as opposed to a cube for instance, in which all sides are equal.

These metals are less dense than lead at room temperature:
Chromium (Cr): Density 7.19 g/cm³
Lithium (Li): Density 0.534 g/cm³
Manganese (Mn): Density 7.21 g/cm³
Radium (Ra): Density 5.5 g/cm³
Silver (Ag): Density 10.49 g/cm³
Titanium (Ti): Density 4.51 g/cm³