Transcript Atomic Structure pp

Atomic Structure
 Atomic number – the number of protons in
the nucleus of an atom ( ID of element )
 Mass number– sum of protons and neutrons
in an atom.
 Actual mass- what an atom actually weighs.
Actual atomic mass
 Mass of a proton = 1.0 x 10 -23 g
 Mass of a neutron = 1.0 x 10 -23 g
1( 1.0 x 10 – 23 ) g
2( 1.0 x 10 – 23 )g
3 ( 1.0 x 10 – 23 )g
Relative atomic mass – the mass of
an atom compared to a standard.

if we say protium is one, then deuterium is
two and tritium will be three.
R-ATM 1
R- ATM 2
R- ATM 3
The real standard is carbon-12
 a Protium atom is 1/12 the weight of a
carbon-12 atom, so it still works out that the
relative atomic mass is still one.
Atomic Mass
 If each element has several isotopes with
their own relative atomic masses, what
number is put on the periodic table?
 Atomic mass ( atomic weight, old school) is
the weighted average of all the naturally
occurring isotopes of that element.
Do the math
 Symbol
R-atm X % = product
35Cl

34.969 x 75.53 = 26.41
 + 37Cl
36.966 x 24.47 = 9.045
Atomic mass of Cl =
35.46amu
 Move the decimal in the % 2 places to the
left before you enter it into the calculator.
Alternate set up
 (R-atm
x
%) +
(R-atm x
%)=
atomic mass
 (34.969 x .7553) + (36.966 x .2447) =35.46
 Repeat for as many isotopes that there are for that
element.