Transcript 3-3 Modern Atomic Theory

3-3 Modern Atomic
Theory
The Structure of the Atom
► The
core
atom has a positively changed central
 Contains Protons and Neutrons
 Protons are positive, equal and opposite to
electrons
 Neutrons do not carry a charge and are slightly
more massive
►1
proton has the mass of about 2000 electrons
► Electrons
move in
space around the
nucleus
► Rutherford
visualized it
as a mini solar system.
Atomic Numbers
► Henry
Moseley found that atoms contain
unique positive charge in their nucleus.
► The
number of protons is called the atomic
number.
The atomic number indicates protons.
Chlorine has 17 protons = atomic number
Practice
► How
many protons and electrons are in a
magnesium atom?
► What
is the name of the element that has
atoms that contain 11 protons.
Ions
► When
an atom gains or loses electrons it
acquires a charge
 Fewer electrons means positive charge
 More electrons means negative charge
 Charge of ion = # protons - # electrons
Sample
► Write
the chemical symbol for the ion with 9
protons and 10 electrons
►Answer
F-
► What
is the symbol of the ion with 13
protons and 10 electrons?
►Answer
►7
Al3+
Protons and 10 electrons?
►N 3-
Isotopes
► Dalton
same.
► Not
said all atoms of an element are the
quite true, ISOTOPES have a different
number of neutrons
► In
nature, elements are almost always
found as a mixture of isotopes
► Isotopes
are usually in the same
percentages.
► To
identify isotopes more specifically
 Use the Mass Number
 Mass Number = (# protons) + (# neutrons)
► To
identify an isotope chemists write the
mass number behind the element symbol
for example Cl-37 indicates that this
chlorine has 20 neutrons, it is written in
symbol form as 3717Cl
► Cl-35 has 18 neutrons and is written as
35 Cl
17
The Mass of an Atom
► Measured
by Atomic Mass Units (AMU)
► The
atomic mass is approximately the same
as the sum of protons and neutrons
► This
is not very precise so Scientists define
it more precisely.
►1
amu is equal to 1/12 the mass of a
carbon-12 atom.
►=
1.66 x 10
► Carbon
–24
grams
12 is the only element with an AMU
equal to protons and neutrons, because of
isotopes
► The
average mass of an element’s atoms is
called the atomic mass.
► AM
= (mass isotope x abundance)+(mass
isotope x abundance)+...
Fundamental Subatomic Particles
Particle
Location
Charge
(C)
Mass (g)
Mass
(AMU)
Proton
Inside
nucleus
+1.602 x 10-19
1.673 x 10-24
1
Neutron
Inside
nucleus
0
1.675 x 10-24
1
Outside
nucleus
-1.602 x 10-19
9.109 x 10
0
Electron
–28