The molecule below has sigma (σ) and pi (π) bonds. How many are of pi (π) type?  

Which gas, krypton or argon, diffuses faster under the same conditions?

 Calculate the standard enthalpy change for the reaction below using the given heats of formation. B2O3(g) + 3COCl2(g) 2BCl3(g) + 3CO2(g)                 ΔHof of B2O3(g) = –1272.8 kJ∙mol–1                               ΔHof of BCl3(g) = –403.8 kJ∙mol–1   ΔHof of COCl2(g) = –218.8 kJ∙mol–1                                 ΔHof of CO2(g) = –393.5 kJ∙mol–1  

Calculate the energy of a photon with a wavelength of 535 nm.   h = 6.626×-34 J∙s and c = 2.998×108 m∙s–1

Which sample represents a larger mass?

Carbon tetrachloride, CCl4,  is a liquid with the density of 1.59 g/mL and molar mass of 153.8 g.  How many moles are present in a 10.0 mL sample of CCl4?

When a 45.0 g sample of a certain metal at 100.0 °C is dropped into a coffee cup calorimeter containing 100.0 g of water at 25.0 °C, the thermal equilibrium is reached at 37.0 °C.  What is the specific heat of the metal?  The specific heat of H2O(l) is 4.184 J·g–1·°C–1. Assume no heat is lost to the walls of the cup and to the surroundings.

In the structure below octet rule is fulfilled for al atoms but lone electron pairs are not shown. Determine the molecular geometry around the N atom in this molecule.

Consider Lewis structures of carbon monoxide, CO, and carbon dioxide, CO2. Which statement best describe the carbon-oxygen bond in these two?    

If element X has the first three ionization energies of these values:  250, 800, and 3340 kJ·mol–1 , what is the most likely formula for the stable ion of X?