NOVA | scienceNOW | Elemental Quiz: Answers

Answers

1. (a) to reflect chemical properties

Position on the chart reflects chemical properties, such as how easily an element combines with others. For instance, the elements in the far right column—helium, neon, argon, and so on—make up the noble gases, which are chemically "aloof." The shape of the chart has changed considerably since the 1860s, when Russian chemist Dmitri Mendeleyev and others first arranged the 60 or so elements known at the time. But amazingly, Mendeleyev was so astute in his grasp of chemical properties that he left gaps in his chart predicting the existence of elements later discovered.

2. (b) the number of protons it has

It's the number of protons, also called the "atomic number," that determines the order of elements. Each atom of hydrogen has a single proton, hence hydrogen is number 1. Helium has two protons in its nucleus and so is number 2. The early periodic charts of the 19th century, devised when subatomic particles like protons were yet unknown, ordered the elements according to what was then called atomic weight—how heavy the element was compared to hydrogen, the lightest element.

3. (a) technetium (element number 43) in 1937

If you know your Greek, you might have guessed technetium is right. (Technetos is the Greek word for artificial.) Element 43 has been glimpsed in the spectra of stars, but it was officially discovered in a laboratory in Italy in 1937. Researchers found it in a sample of molybdenum (element 42) that had been bombarded with heavy hydrogen nuclei in the University of California, Berkeley cyclotron. Technetium is one of several elements Dmitri Mendeleyev predicted and left a gap for in his periodic table.

4. (c) an international group of chemists

In the early days, researchers chose names for their finds. Marie Curie named element 84 "polonium" after her beloved homeland, Poland, for example. But this tradition led to confusion, with some elements having multiple names. Today, discoverers may suggest names, but an international council of chemists makes the final call. Elements are usually named after a mythological figure (neptunium, plutonium), a place (berkelium, californium), or in honor of a scientist (mendelevium, curium).

5. (a) a smoke detector

You may be surprised to hear that common smoke detectors contain an artificially produced element made in nuclear reactors. The element, called americium, was discovered in 1945 during the Manhattan Project, and yes, it's radioactive. But the quantity of americium used in a smoke detector—less than 1/5,000ths of a gram—is so tiny that it poses no health hazard. The radioactive element creates charged particles called ions within the chamber of the detector. When smoke absorbs these ions, an electric current is cut off, which then sets off an alarm.

6. (c) in debris from a hydrogen bomb test

The first large-scale hydrogen bomb test was conducted in the Pacific in November, 1952. The following month, Albert Ghiorso and colleagues at the University of California, Berkeley identified two new heavy elements: 99, later called einsteinium, and 100, dubbed fermium in honor of Italian physicist Enrico Fermi. The findings, part of Cold War research, were kept secret until 1955, by which time scientists at the Nobel Institute of Physics had also synthesized element 100 in a particle accelerator in Stockholm.

7. (b) lead

Helium, oxygen, calcium, nickel, tin, and lead all have magic numbers of protons, but lead, with 82 protons, is the heaviest of the bunch. Why are these elements more stable? The "magic" lies not in the supernatural but in basic nuclear structure: within the nucleus, protons are arranged in a series of shells that can either be filled or incomplete. A magic number of protons leaves no shell incomplete, and an element with filled shells is less likely to engage in nuclear reactions.

8. (a) 30 seconds

Thirty seconds is a blip in human time but an extraordinary life for a superheavy element. Some of 114's neighbors last only millionths of a second before they break apart. Nuclear chemist Ken Moody notes that the lifespan of the synthesized atom of 114 proves that a so-called "Island of Stability" exists. But he and colleagues haven't reached it yet; to land on its shores will require making an isotope of 114 with a magic number of neutrons as well as protons. This feat may require a new breed of particle accelerators—not to mention perseverance, funding, and luck.