Questions by topic

Orbitals, the regions around an atom’s nucleus likely to be occupied by electrons, are grouped into subshells identified by energy level (1, 2, 3, 4 and so on) and orbital shape (s, p, d, and f). The 3d subshell contains five orbitals, each able to hold up to 2 electrons, a total of 10 electrons if all filled. Transition metals Read more...

Most liquids contract when cooled, getting denser until they freeze into a solid. Their moving molecules lose kinetic energy, slowing them down, so they become prone to the attractive forces of nearby molecules drawing them closer together. Water exhibits this normal behavior down to 4 degrees Celsius (or 39.2 degrees Fahrenheit) where its density reaches a peak, but cooling actually Read more...

Glow sticks contain hydrogen peroxide solution and a separate sealed glass tube of diphenyl oxalate ester solution mixed with a fluorescent dye. Bending the glowstick breaks the inner glass tube, mixing the two solutions, and starts a chemical reaction. The reaction makes 1,2-dioxetanedione, a cyclic dimer of carbon dioxide, which rapidly decomposes to carbon dioxide, releasing energy that excites electrons Read more...

Sound travels almost 3 times as fast in helium gas than in normal air because helium is less dense. Contrary to common perception, helium does not make the voice high-pitched, because voice pitch is determined by the vibration frequency of the vocal chords generating the sound. So, while the fundamental pitch of the voice is actually unchanged, what helium does Read more...

An ideal gas is a scientific concept underpinning the Ideal Gas Law, of a theoretical gas with strictly defined properties for the purpose of understanding, predicting, and explaining the behavior of real gases under different conditions of temperature, pressure and volume. In an ideal gas: Molecules are spheres which collide elastically with each other and the container walls, so the Read more...

A temperature of minus 40 degrees is the same in both Celsius and Fahrenheit. It is the only temperature point on the F and C scales where this occurs. Read more...

The light we see from the sun is made up of a rainbow spectrum of colors from red through blue to violet. As light passes through the Earth’s atmosphere, it hits small gas molecules and particles in the air and gets scattered in different directions. This is known as Rayleigh scattering. As blue light has more energy than, say, red Read more...

An ion is an atom or molecule carrying an electrical charge because it has an unequal number of protons and electrons. By convention, protons are considered positively charged, and electrons negative and a net electrical charge results whenever there is more of one than the other. An ion with more protons than electrons carries a net positive charge and is Read more...

Most commercial aircraft cabin windows are made of three plastic panes, each separated by a small air gap. The tiny hole at the bottom of the window is a bleed hole through the center pane to equalize the pressure inside the window unit with the cabin air pressure. By design, this ensures it is the outermost window pane bearing the Read more...