Neptunium is a radioactive, silvery metal with the atomic number 93. It is a synthetic element and was the first element beyond uranium to be synthesized. It was named after the planet Neptune.
Helium is the second lightest gas and has the atomic number 2. Because it is so light, it can escape the Earth's gravitational pull and so is rare on Earth. It was found on the sun, and was named after "helios," the Greek name for the sun.
Plutonium is another transuranic element and was named after the planet Pluto. It was created in 1940 through the bombardment of uranium by deuterons. It's a silvery white metal whose most important isotope is Pu 239.
Selenium is not only an element but a nutrient that the human body needs in trace amounts. Its atomic number is 34. Selenium is not a metal but has a gray luster that looks metallic. Though it can be found as a free element, selenium is usually a byproduct of copper mining. Selenium was named after the moon.
Uranium, with an atomic number of 92, was named after the planet Uranus.Learn more about Atoms & Molecules