ATOM
~ 10-10 m
electron
Mass 9 x 10-31 kg
nucleus
Mass > 10-26 kg
~ 1 – 7 x 10-15 m (1 – 7 fermi)
The Spacious Atom
atoms are dominantly empty space:
electron orbits
If an oxygen atom had
a total radius of 100
km, the nucleus would
be a ~1 m diameter
sphere in the middle.
Electrons in Orbit
In a simplistic model, electrons float around the nucleus in
energy levels called shells.
electron orbits
As the number of
electrons increases,
they start to fill shells
farther out from the
nucleus.
In most cases, electrons
are lost or gained only
from the outermost
shell.
Atom
Nucleus
Most of the atom is…
• empty space!
Subatomic Particles
Particle
Symbol
Charge
Relative
Mass(unit)
Electron
e-
1-
0
Proton
p+
1+
1
Neutron
n
0
1
Most of the mass of the atom is…
• formed by the nucleus.
Atomic Number, Z (nuclear charge)
is the total number of protons in the atom.
Symbol
Na
11
Atomic Number
Atoms are identified by their proton numbers.
All atoms of an element have the
same number of protons
11 protons
Sodium
11
Na
Mass Number, A (nucleon number)
Counts the number
of
protons and neutrons
in an atom
A= p+ + n0
Protons and neutrons (together) are called “nucleons.”
Atomic Symbols
 Show the mass number and atomic number
 Give the symbol of the element
(A)mass number
23Na
11
(Z)atomic number
sodium-23
Learning Check 1
An atom of zinc has a mass number of 65.
A. Number of protons in the zinc atom
1) 30
2) 35
3) 65
B. Number of neutrons in the zinc atom
1) 30
2) 35
3) 65
C. What is the mass number of a zinc isotope
with 37 neutrons?
1) 37
2) 65
3) 67
Learning Check 2
Write the atomic symbols for atoms with the
following:
A. 8 p+, 8 n, 8 eB. 17p+, 20n, 17eC. 47p+, 60 n, 47 e-
___________
___________
___________
Learning Check 3
An atom has 14 protons and 20 neutrons.
A. Its atomic number is
1) 14
2) 16
3) 34
B. Its mass number is
1) 14
2) 16
C. The element is
1) Si
2) Ca
3) 34
3) Se
PERIODIC TABLE
Watch the VIDEO
http://www.youtube.com/watch?v=ckCW_dxmYNI
http://www.youtube.com/watch?v=RCNkZ-S5-Q4