Download Atomic Structure

Atomic Structure
The Atom
-
smallest particle of an
element that retains the
chemical properties of that
element.
-
Composed of three
subatomic particles:
protons, neutrons, and
electrons.
History
Democritus
~400BC
Said that the nature of things
consisted of an infinite number
of extremely small particles
which he called atoms. (Greek
atomos – indivisible).
Completely theoretical- no
experiments!
Which of these does not agree with modern theory?
John Dalton
~ Early 1800’s
Dalton’s Atomic Theory
1. All matter is composed of extremely small
particles called atoms.
2. Atoms of a given element are identical in
size, mass, and other properties. Atoms
of different elements are not the same.
3. Atoms cannot be subdivided, created, or
destroyed.
4. Atoms of different elements can combine to
form compounds.
5. In chemical reactions atoms are combined,
separated, or rearranged.
J.J. Thomson
1897
–
Discovered
Electron.
* Used a cathode ray to
identify the electron by
measuring its response to
both electric and
magnetic fields.
Interactive Cathode Ray Tube
* “Plum Pudding” Model
http://www-outreach.phy.cam.ac.uk/camphy/nucleus/side1_nucleus.gif
Ernest Rutherford
1911 Gold Foil Experiment:
(Geiger and Marsden).
* Dense positively charged
nucleus. (Most of the mass of
the atom.)
*Most of the atom is empty space.
*Electrons orbited the nucleus.
Gold Foil Interactive Model
Neils Bohr
1913 Added the
idea of electron
energy levels to
Rutherford’s
model.
http://csep10.phys.utk.edu/astr162/lect/light/bohr.html
James Chadwick
1932 Discovered a particle
which increased the mass
of an atom without
changing the charge. This
neutral particle became
known as the neutron.
Modern Theory
Regions of the Atom
I. The Nucleus
- very small, dense region near the
center of the atom containing nearly
all the mass of an atom (protons
and neutrons).
Nucleons
Protons
– positively charged (+1) with a mass of
1 amu (atomic mass unit) or 1.673x1027 kg (Symbol: p+)
Neutrons –
- neutrally charged (0) with a mass of 1
amu or 1.675x10-27 kg (Symbol: no)
Regions of the Atom
II. The Electron Cloud
-
region surrounding the nucleus occupied
by negatively charged subatomic particles
called electrons. This region is very large
but mostly empty space!
Electrons
- negatively charged (-1) with a mass of
approximately 0 amu or 9.109 x 10-31 kg.
Its mass is so small that it practically
makes no contribution to the total mass
of the atom (Symbol: e-)
Overview of the Atom

Summary of Subatomic Particles
Particle
Symbol
Charge
Mass (amu)
proton
p+
+1
1
neutron
n0
0
1
Electron
e-
-1
0
Neutrality

Atoms are electrically neutral, they
do not have a charge, and
therefore, the total number of
electrons must equal the total
number of protons.
# p+ = # e -
Total Mass

An atom’s total mass is primarily
composed of only the protons and
neutrons (the nucleus). The
electron’s mass is so small that it
does not contribute!
Mass = p+ + no
Important Information About
the Atom
Atomic Number



The atomic number is the
“fingerprint” of an element
(identifies the element).
If the number of protons changes
then the identity of the element
changes with it!
Atomic Number (Z) – the number
of protons in the nucleus of each
atom of that element
Z = # of protons
Mass Number
Mass Number (A) – the total number of
protons and neutrons in the nucleus of
an atom.
A= protons + neutrons
Isotopes – atoms of the same element with
different numbers of neutrons. This
causes them to have different mass
numbers.
14
6
C
or
C - 14
Practice with Particles
Give the number of each subatomic particle in
the following isotope.
14
6
C
Remember:
Z = 6 so
A = 14 so
or
C - 14
Z = # of protons and
p+=6, and e-=6
14 = p++no
14 = 6 + no
no = 8
# p+ = # e-
More Practice
Isotope
silicon-28
silicon-29
silicon-30
copper-65
cesium-133
carbon-14
# p+
# n0
# e-
A
Z