Which of these elements is a metal?

hafnium (Hf)

radon (Rn)

silicon (Si)

sulfur (S)

selenium (Se)

What structural units make up network solids? O A. Nonmetal atoms O B. Molecules O C. Metal atoms O D. lons

Why is a measured amount of water needed to determine the specific heat of a metal object?

How many moles are there in 25.0 g of sodium?

How to calculate the number of atoms, molecules, or ions

How many electrons would be exchanged from lithium and fluorine

Which of the following represents a chemical change? Bending a wire Freezing of water Fireworks exploding Melting of a wax candle

5.00 L of a gas is collected at 100K and then allowed to expand to 20.0 L. What must the new temperature be in order to maintain the same pressure? A. 400 °C B. 127 °C C. 223 °C D. 627°C

Before the initial explosion was the matter hot or cold

Which of the following atoms has seven valence electrons? chlorine (Cl) nitrogen (N) manganese (Mn) oxygen (O)

A.) During an experiment, a student adds 2.90 g of CaO to 400.0 mL of 1.500 M HCl. The student observes a temperature increase of 6.00 °C. Assuming the solution/'s final volume is 400.0 mL, the density if 1.00 g/mL, and the heat capacity is 4.