Which of these pairs of elements have the same number of valence electrons?

phosphorus (P) and chlorine (Cl)

berylium (Be) and calcium (Ca)

chlorine (Cl) and helium (He)

oxygen (O) and carbon (C)

1. What is the oxidation number for the silver ion in tarnish?

Humans are responsible for some of the negative changes that occur in nature because

A man has 50.0 ml bottle completely filled with 163 g of a slimy green liquid. What is the density of the liquid?

A hydrate of CoCl2 has a mass of 17.40 g before heating. After heating, the mass of the anhydrous compound is found to be 10.27 g. Explain how you would determine the formula of the hydrate and then write out the full name of the hydrate.

How many atoms are in 131.97 liters of water vapor at STP? A) 6.023 * 1023 B) 3.54846 * 1024 C) 3.548 * 1024 D) 1.0645 * 1025

Cobalt fluoride crystallizes in a closest packed array of fluoride ions, with the cobalt ions filling one-half of the octahedral holes. What is the formula of this compound?

When you get into a parked car in the summer time, the metal clip is hot and the seat belt fabric is not. What has a higher specific heat, the metal clip or the seat belt fabric? Think about the definition of specific heat.

A laboratory procedure calls for making 600.0mL of a 1.1M KNO3 solution. How much KNO3 in grams is needed?

How do you make good grades?

What will happen to the pressure inside a rigid container of gas if some of the gas is allowed to escape? (Assuming no change in temperature)