Matter & Energy


Matter is composed of atoms or groups of atoms called molecules. The arrangement of particles in a material depends on the physical state of the substance. In a solid, particles form a compact structure that resists flow. Particles in a liquid have more energy than those in a solid. They can flow past one another, but they remain close. Particles in a gas have the most energy. They move rapidly and are separated from one another by relatively large distances.

Dubnium

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Dubnium, symbol Db, chemical element with atomic number 105, produced artificially by nuclear fusion (in which an element with larger atoms is produced by fusing together two smaller atoms from other elements). Each dubnium atom has a very large nucleus, or central mass, containing positively charged particles called protons and neutral particles called neutrons. The large number of particles in the nucleus makes the atom unstable and causes the atom to split apart into smaller components soon after it is created. To honor the Joint Institute of Nuclear Research (JINR) located in Dubna, Russia, where element 105 was first created in 1970, the International Union of Pure and Applied Chemistry officially named this element dubnium. Element 105 was previously called hahnium, after German physical chemist Otto Hahn, a pioneer in the field of nuclear fission.

Dubnium has the atomic number 105, which means that each Db atom contains 105 protons. Scientists have created several isotopes of dubnium, or forms of the element that contain different numbers of neutrons in the nucleus. For example, dubnium-262 contains 105 protons and 157 neutrons (105 protons + 157 neutrons = atomic mass 262). Similarly, dubnium-263 contains 105 protons and 158 neutrons.

Russian scientists first created dubnium by bombarding atoms of the element americium with neon atoms, creating unstable dubnium isotopes. Because the nucleus of the dubnium atom contains so many particles, the atom undergoes spontaneous fission, a process in which the atom quickly breaks into smaller “daughter” components. When the atom splits, it releases energy in the form of electromagnetic waves and electrically charged bits of matter. This energy is known as radiation (see Radioactivity).

Dubnium belongs to Group 5 (Vb) on the periodic table, which also contains the naturally occurring metals vanadium (V), niobium (Nb), and tantalum (Ta). Because elements in the same group, or column, on the periodic table, scientists expected dubnium to be a corrosion-resistant, shiny, silvery metal that reacts with oxygen under certain conditions. However, scientific observations reveal that dubnium deviates from other Group 5 elements and appears to share complex properties of the elements plutonium (Pu) and protactinium (Pa) instead. Scientists theorize that the properties of dubnium may diverge from other Group 5 elements because the massive positive charge of all the protons in the Db nucleus causes the surrounding electrons to orbit at rates approaching the speed of light. This phenomenon, known as the relativistic effect, may alter the expected paths of the electrons spinning around the dubnium nucleus, possibly affecting the chemical properties of this element.