Week 3

Based on Dalton's atomic theory, which is true?

An iron rod is made up of an incredibly large number of individual iron atoms.

Which isotope is the most abundant, based on the atomic mass of hydrogen?

1/1 H The atomic mass given in the periodic table of the elements is the average mass number, accounting for the relative abundances of different isotopes. The mass of H is 1.008amu. Therefore, it is clear that the 1/1 H is the most abundant isotope of hydrogen, as the average weight of hydrogen is closest to 1. Note that the weight of 2/1 H is 2amu and the weight of 3/1 H is 3amu.

Oxygen is estimated to make up 28.7% of the mass of ordinary matter on Earth, while Aluminum makes up 1.6%. Estimate the ratio of the number of oxygen atoms to the number of Aluminum atoms on Earth.

30 Assume a 100. g representative sample of ordinary matter on Earth. For each element, use the mass percentage to find the number of grams and the atomic mass to find the number of moles, beginning with oxygen. 100. g x (28.7% / 100.%) x (1.00 mol O / 15.999 g O) = 1.79 mol O Now Aluminum: 100. g x (1.6% / 100.%) x (1.00 mol Al / 26.982 g Al) = 0.059 mol Al Finally, divide the numbers of moles to find the mole ratio, which is equal to the ratio of atoms. (1.79 mol / 0.059 mol) = 30.34 The answer should be rounded to two significant figures, so O atoms are about 30. times more common than Al atoms.

How many protons are present in an isotope of nitrogen that has a mass number of 15?

7

A molecular formula of a molecule is C2H8. What is the empirical formula for this molecule?

CH4

Which subatomic particle is negatively charged and is found outside of the nucleus?

Electron

What is the chemical symbol for iron?

Fe

Which scientist's experiment determined the mass of an electron?

Millikan

When nitrogen gas and oxygen gas react, they can form a compound with a mass ratio of nitrogen to oxygen of either 1:1.143 or of 1:2.286. What law do these compounds illustrate?

The law of multiple proportions

What is true about the mass of protons and neutrons?

They have masses slightly greater than 1 amu.