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ch 2 - atoms, molecules, and ions


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what are the main subatomic particles of atoms?
protons (+ charge), neutrons (neutral), electrons (- charge)

protons and neutrons are located in the nucleus (nucleus diameter is approx 10**-13 cm)

electrons move around the nucleus, avg distance 10**-8 cm from the center
what is the charge for protons? electrons?
postive charged protons: +1.602 x 10**-19 C

negative charged electrons: -1.602 x 10**-19 C
what is atomic number?
the number of protons and electrons in an atom (if not equal they are ions)

chemical property of the atom is determined by the number of electrons

note: the number of neutrons can vary which gives rise to isotopes
what is atomic mass?
atomic mass = number of protons + number of neutrons, e.g.

13 (atomic mass)
6 (atomic number)

--> 6 protons, 6 electrons, 7 neutrons
what is a molecule?
molecule: the assembly of two or more atoms

the atoms are held together by chemical bonds

molecules have a molecular formula
molecular mass?
the sum of the atomic mass for all atoms in a molecule

e.g. H2O; 1 + 1 + 16 amu (atomic mass units)
what are ions? charge?
cation: + charged ion, formed when one or more electrons is lost

anion: - charged ion, formed when one or more electrons is added

charge = atomic number - number of electrons
what are polyatomic ions?
polyatomic ions are composed of several cation and anion atoms.

e.g. two Br- anions are combined with one Ca2+ cation to form CaBr2
what is a structural formula?
shows the arrangement of the atoms in a molecular formula, e.g. water:

What are acids?
Acids generate H+ cation and an anion when dissolved in water.

e.g. H2S + H20 -> H+ + HS-

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