An element has: Atomic number 13 Three energy levels occupied Three valence electrons A neutral atom of this element loses three electrons. Which statement must be true?

An unknown sample exhibits all of the following: It is a pure substance. It emits characteristic spectral lines. All atoms possess the same atomic number. Atoms differ in neutron count. The element tends to gain one electron in chemical reactions. Which conclusion is best supported?

Four elements are identified only by atomic number: P: 3 Q: 11 R: 17 S: 18 Which comparison is most likely true?

As you move from left to right across a period in the periodic table, atomic radius generally:

A neutral atom: Contains 20 neutrons. Has 18 electrons. Belongs to the noble gases. Has a lower mass number than another isotope of the same element. Which statement must be true?

A laboratory bench has a length of {L} m. Convert this length to centimeters.  Enter your answer as a number only.

A sealed container recovered from a laboratory contains a colorless gas. Scientists make the following observations: The gas is a pure substance. Spectroscopic analysis shows a single set of emission lines. Every atom in the sample contains 18 protons. Approximately 60% of the atoms contain 22 neutrons, while 40% contain 20 neutrons. The gas is extremely unreactive under normal conditions. Repeated mass measurements of the sample are highly precise but consistently 2% lower than the accepted value. Which conclusion is most strongly supported by all of the evidence?

Atoms of same element with different numbers of neutrons are called:

The visible hydrogen spectrum has a blue colored line at 487 nm. Assume that nf = 2. In the Rydberg equation the value of ni for this blue line is _________.    1nm = 10^-9 m      

Methanol has a normal boiling point of 64.6°C and a heat of vaporization, ΔHvap, of 35.2 kJ/mol.  What is the vapor pressure(torr) of methanol at 12.0°C ?