Metals Denser Than Lead at Room Temperature (Pt 1) Quiz

Answer:

Americium (Am), atomic number 95. With a density of approximately 12.0 grams per cubic centimeter, Americium is about 6% denser than lead. Each americium atom has 13 more protons and neutrons in its nucleus than a lead atom. Americium is primarily a man-made element produced in nuclear reactors, and does not exist in nature in significant quantities. Highly radioactive, americium's special use is found in some ionization smoke detectors.

Californium (Cf) atomic number 98. At 15.1 grams per cubic centimeter, Californium is over 33% denser than lead. It too is a synthetic element, not existing naturally on Earth. This radioactive rare metal is one of the most expensive substances in the world, produced in minute quantities (total global production being only a few grams per year). Among its several uses, as a neutron source, is in neutron radiography to see inside dense objects, like when inspecting aircraft parts for cracks.

Gold (Au), atomic number 79, 19.3 grams per cubic centimeter, making it about 70% denser than lead. Yes, a lead atom (atomic number 82) is heavier than a gold atom (atomic number 79), but density is about mass per unit volume. Atoms in gold are packed together more efficiently, leading to more mass in the same amount of space, accounting for gold's greater density; a solid gold cube would weigh almost twice as much as the exact same size cube of lead. Gold is a precious metal; used in jewelry (gold is resistant to tarnishing), electronics, and as a financial standard.

Iridium (Ir), atomic number 77, is a member of the Platinum Group Metals which, in addition to being rare, are also known for their high density, and resistance to wear and corrosion. Iridium is very rare in the Earth's crust; but it is much more common in asteroids and meteors. At 22.56 grams per cubic centimeter iridium is not just a little denser than lead, it is nearly twice as dense as lead. A cube of it with 1-inch sides would weigh about 1.4 pounds (0.65 kg). Iridium is the most corrosion-resistant metal, and is one of the two densest elements known to exist on Earth, along with osmium.

Speaking of osmium (Os), atomic number 76, it too is twice as dense as lead (22.59 grams per cubic centimeter). It is hard and brittle and is a bluish-white metal also of the Platinum Group Metals. Osmium gets its name from the Greek word osme, meaning "smell"; in powdered form, it slowly oxidizes in air to form osmium tetroxide, which has a pungent smell similar to chlorine. Like iridium, osmium is more abundant in meteorites than in the Earth's crust, leading to the confirmation amongst geologists that support the theory that an asteroid impact caused the dinosaur extinction.

Palladium (Pd), atomic number 46, has a density of 12.02 grams per cubic centimeter. This rare and shiny Platinum Group Metal was discovered in 1803 by William Hyde Wollaston, who named it after the asteroid Pallas. Over 80% of the use of palladium is for catalytic converters in gasoline vehicles. It is also used in electronics, jewelry, hydrogen purifiers, and in dentistry.

Plutonium (Pu) has a density of 19.86 grams per cubic centimeter. It is primarily man-made and radioactive, well-known for its use in nuclear weapons and reactors, and at room temperature is highly reactive. It feels warm to the touch at room temperature due to the energy released by radioactive decay, and so it must be handled using specialized gloveboxes that guard against inhaling the plutonium dust, which would be terribly hazardous.

Rhenium (Re) has a density of about 21.02 grams per cubic centimeter. One of the rarest elements in Earth's crust, Rhenium has the second-highest melting point of all elements (3186 °C / 5767 °F); only tungsten has a higher melting point. Its rarity makes it a very expensive metal, and it is used in high-temperature superalloys for jet engine production parts, such as turbine blades and combustion chambers.

Rhodium's (Rh) density is 12.41 grams per cubic centimeter, and is one of the most expensive precious Platinum Group Metals. It was discovered in 1803 by William Hyde Wollaston soon after he discovered palladium. Over 80% of the world's supply of rhodium comes from South Africa, and the number one use of it is in catalytic converters. "Rhodium Plating" uses rhodium's brilliant white reflectivity and resistance to tarnishing in jewelry plating.

Tantalum (Ta), 16.68 grams per cubic centimeter. Tantalum has a crystal structure, efficiently packing its atoms in a stable way which contributes to its high density. It has the fourth highest melting point of all metals, making it very helpful in high-temperature uses like parts for furnaces, or jet engines. It is very resistant to corrosion due to an oxide layer on its surface which makes it useful for capacitors in smartphones but also very importantly, for human body medical implants.

Thorium (Th) is a little denser than lead with11.7 grams per cubic centimeter. It too has a crystal structure making it more efficiently dense at room temperature. It has a half-life of about the same number of years as the age of the universe itself, but its radioactivity level is so low that it's possible to handle it safely. Safeguards should still be taken because, although the alpha particles it emits so slowly can't penetrate skin, they can still be hazardous if inhaled, ingested, or enter the body through a wound. It is used in some high-tech alloys and nuclear applications.

These metals are less dense than lead. Here are their density levels at room temperature in grams per cubic centimeter:
Iron 7.87
Magnesium 1.737
Molybdenum 10.223
Strontium 2.582
Vanadium 6.0
Zinc 7.14