Se dau atomii: Mg, Br, H, O. Scrie formulele chimice ale substantelor obtinute prin combinarea atomilor specificati ( cate 2 tipuri de atomi, identici sau diferiti). Cerinte: 1. Denumirea substantelor 2. Tipul legaturii dintre atomi 3. Modelarea formarii legaturii chimice indicatii Mg = grupaII A; Br = grupa VII A; O = grupa VI A

Nebulae are enormous clouds in outer space. they are made mostly of hydrogen gas, helium gas, and dust. some nebulae glow brightly, while others do not. the stars that people see are huge, bright balls of glowing gas. they are made mostly of hydrogen and helium. which statement correctly describes other ways in which nebulae and stars are different? a. stars can form inside a nebula but a nebula can never be produced by any star. b. a star always has a higher density than a nebula. c. stars can never form inside a nebula but a nebula can be produced by any star. d. a nebula always has a higher density than a star.

In general metals get as you move from left to right across the periodic table.

Which of these describes the rate of this chemical reaction? h2 + cl2 → 2 hcl a. an increase in the concentration of hcl and h2 with time b. an increase in the concentration of hcl with time c. an increase in h2 and cl2 with time d. a decrease in hcl and cl2 with time