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Elements
Differences in the atoms that make up the elements
Current model of the atom
Nuclear atomAlmost all of the mass of the atom is
located in the nucleusAll of the volume of the atom is made
up by the electron cloud, which is mostly empty space
The Nuclear Atom
Proton
Has a charge of 1+Has a mass of approximately 1
amu (atomic mass unit)Found in the nucleusThe number of protons identifies
the type of atomThe number of protons = the
atomic number of the element
Electrons
Have a charge of 1-Have a negligible mass (1/2000 of a
proton)Found in the electron cloud in
orbitalsAre the particle of the atom that are
responsible for the chemical bondsNeutral atoms have the same
number of electrons as protons
Neutrons
Are neutral, have no chargeHave a mass of approximately 1
amuFound in the nucleusAre the particle of the atom that is
responsible for isotopes
What is an Isotope?
Atoms with the same number of protons (so they are the same element)
But they have different numbers of neutrons
Thus, they are atoms of the same element that have different masses
Two isotopes of Sodium
How do we write that?
23
11
Na
Or
Na-23
Na-23 has
11 protons (atomic number)11 electrons (neutral atom)12 neutrons (atomic mass of 23
amu)
Na-23 is an isotope
It has the same number of protons as other atoms of sodium
It is a neutral atom (no charge, same number of electrons as protons)
It has different number of neutrons than other sodium atoms
Atomic Numbers
Atomic number is the number of protons in an atom
Mass number is the sum of the number of neutrons and the number of protons in a given atom
The atomic mass number on the periodic table is a weighted average mass of all known isotopes of that element