Exam 2: Atoms and Molecules

Naturally occurring lithium (Li)consists of only two isotopes, Li-6 (6.02 u)and Li-7 (7.02 u), where the isotopic masses are given in parentheses. Use the periodic table and determine which isotope is present in the larger percentage in the natural element.

The most accurate way to determine atomic mass is with a mass spectrometer.

The average relative mass of an ozone molecule is 48.0 u. An ozone molecule contains only oxygen atoms. What does this molecular weight indicate about the formula of the ozone molecule?

Isotopes of the same element always have the same number of neutrons.

How many silicon atoms (Si)are contained in a 12.5 g sample of silicon?

Atoms are neutral. How can they have no charge?

Electrons do not make an important contribution to the mass of an atom.

You discover a new element which consists of two isotopes.  The first isotope, ²⁴³X (mass = 242.45 u)  comprises 40.000% of the total.  The second isotope, ²⁴⁸X (mass = 247.11 u)accounts for the rest.  What would be the average atomic mass for your new element?

The number of Cr atoms in a 26.0 g sample of chromium is x. How many atoms, expressed in terms of x, would be contained in 26.98 g of aluminum (Al)?

A molecular formula

Approximately, how many atoms of beryllium would be required to equal the mass of 10 atoms of aluminum?

How many grams of iron (Fe)is contained in 15.8 g of Fe(OH)₃?

One Avogadro's number of iron (Fe)atoms would weigh _____ .

The charge of the nucleus depends only on the atomic number.

The symbols for elements with accepted names

An isotope of gallium consisting of 31 protons and 37 neutrons can be represented using the symbol shown below.