unit 3 review Flashcards
to take a weighted average of all the naturally occurring isotopes of an element in order to arrive at an average mass, you would
multiply the mass of each isotope by the decimal fraction representing its abundance naturally, then add all these products together.
isotopes are atoms of the same element that have different
masses
the isotope uranimiun-235 has 92 protons and 143 neutrons. therefore it’s mass number is
235
the atomic number of an element is
the number of protons in each atom of the element
mass number is
the total number of protons and neutrons in an atom of an element
most of an atom is
empty
cathode rays are composed of particles that are known as
electrons
except for in the simplest type of hydrogen atom, all nuclei consist of
protons and neutrons
In 1911, Ernest Rutherford conducted his now famous goldfoil experiment. During the experiment, alpha particles bombarded a thin piece of gold foil. The alpha particles were expected to pass easily through the gold foil. Every now and then, however, an alpha particle bounced back—an unexpected result. Rutherford concluded that these particles were striking
a tiny region with positive charge
the radii of atoms are expressed in
picometers
If two or more compounds are composed of the same two elements, then the ratio of the masses of the second element that is combined with a certain mass of the first element is always a ratio of small whole numbers. This statement is called the law of
multiple porportions
The fact that every sample of a particular chemical compound contains the same elements in exactly the same proportions by mass is known as the law of
definite proportions
In an experiment, Anna and Rachel discover that their sample of table salt, also known as sodium chloride, NaCl, consists of 39.34% by mass sodium, Na, and 60.66% by mass chlorine, Cl. Later, Anna wonders what the percentage of Na might be in the table salt in her saltshaker at home. Rachel tells her, correctly, that it is
39.34
In 1808, John Dalton established his atomic theory. Which of the following is NOT part of Dalton’s atomic theory?
An atom consists of a nucleus and a cloud of electrons.
Using improved chemistry equipment in the late 1700s, chemists observed that mass is neither created nor destroyed in a chemical reaction. This scientific law is called the law of
conservation of mass
