The what of an element is the average mass of all isotopes of that element

Which of the following would have to gain two electrons in order to achieve a noble gas electron configuration? O Sr Na Se Br

If the half-life of a radioactive material is 8 years, how many years will it take for one-half of the original amount of material to decay?

How many grams of cl2o7 react with an excess of h2o to form 56.2g of hclo4

In a mixture of He, Ne, and Xe gases with a total pressure of 925 atm, if there is 10.5 g of each gas in the mixture, what is the partial pressure of Xe?

Blue light had a frequency of 6.98*10^14 Hertz. What is the wavelength of blue light in nanometers? Why?

An aqueous solution at 25 °C has a pOH of 12.42. Calculate the pH. Round your answer to 2 decimal places

A student records the mass of a piece of iron. The iron is then left outside until it rusts. What type of reaction occurs, and how does the mass of the object after rusting compare with its original mass?

Which one is a true statement about endothermic reactions? A. Energy from an outside source is continuously being added. B. More heat is given off than is put into the reaction. C. The reactants have less heat energy than the last products. D.

How is the partial pressure of a gas in a mixture calculated?

Part II. Formulas From Names Write the chemical formula of the covalent compounds below. 11. Carbon dioxide CO2