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dubnium

(Encyclopedia)dubnium do͞obˈnēəm [key], artificially produced radioactive chemical element; symbol Db; at. no. 105; mass number of most stable isotope 268; m.p., b.p., and sp. gr. unknown; valence +5. Situated ...

concentration

(Encyclopedia)concentration, in chemistry, measure of the relative proportions of two or more quantities in a mixture. The concentration of a solute is very important in studying chemical reactions because it deter...

Priestley, Joseph

(Encyclopedia)Priestley, Joseph, 1733–1804, English theologian and scientist. He prepared for the Presbyterian ministry and served several churches in England as pastor but gradually rejected orthodox Calvinism a...

rutherfordium

(Encyclopedia)rutherfordium rŭᵺˌərfôrˈdēəm [key], artificially produced radioactive chemical element; symbol Rf; at. no. 104; mass number of most stable isotope 265; m.p., b.p., and sp. gr. unknown; valenc...

activation energy

(Encyclopedia)CE5 Energy profile of an exothermic reaction: Although the total energy of the products is less than that of the reactants, the activation energy must be added to weaken or break existing bonds bef...

oganesson

(Encyclopedia)oganesson ōˈgənĕsˌən [key], artificially produced radioactive chemical element; symbol Og; at. no. 118; mass number of most stable isotope 294; m.p., b.p., sp. gr., and valence unknown. Situated...

Whistler, James Abbott McNeill

(Encyclopedia)Whistler, James Abbott McNeill, 1834–1903, American painter, etcher, wit, and eccentric, b. Lowell, Mass. Whistler was dismissed from West Point for insufficient knowledge of chemistry and from the ...

space medicine

(Encyclopedia)space medicine, study of the medical and biological effects of space travel on living organisms. The principal aim is to discover how well and for how long humans can withstand the extreme conditions ...

manganese

(Encyclopedia)manganese măngˈgənēs, mănˈ– [key] [Lat.,=magnet], metallic chemical element; symbol Mn; at. no. 25; at. wt. 54.93805; m.p. about 1,244℃; b.p. about 1,962℃; sp. gr. 7.2 to 7.45, depending o...

diffusion

(Encyclopedia)diffusion, in chemistry, the spontaneous migration of substances from regions where their concentration is high to regions where their concentration is low. Diffusion is important in many life process...