Transcript Atomic Structure

Atomic Structure
and
Subatomic Particles
Can you see an atom?
• Technically, you cannot "see" anything smaller than the shortest
wavelength of light that you can see it with.
• But there are ways to "visualize" it, like Atomic Force Microscopy. But
these are all just measurements converted to computer images, and
are not in any real sense "seeing" the atom.
• You can't see atoms in any normal sense of using an optical
microscope.
• You don't get an optical image, but it does allow you to map out an
image of the atoms of a molecule. To do this you use a metallic tip
which interacts with the atoms you want to image. As you move the
tip over the atoms, you pass a current, called a tunneling current,
between the tip and the atom. This current is extremely sensitive to
the distance between the atom and the tip.
- REMEMBER FROM: Elements,
Mixtures, and Compounds -
Element
- a pure substance made up of one
type of atom.
- organized on periodic table
- each element has a unique
number of protons…its atomic number
Atomic Structure:
Atoms contain three subatomic particles…
These are
1. Protons…positive charge
located in
2. Neutrons…neutral charge
NUCLEUS!
3. Electrons…negative charge
Electrons surround
the nucleus in
orbitals
Atomic Structure
An atom is considered electrically neutral.
Electrically neutral means the number of
protons (+) = the number of electrons (-)
4 red protons = 4 blue electrons
Relative
Particle
Symbol
electrical
charge
Relative
Actual
mass
mass (g)
Electron
e-
1-
1/1840
9.11 × 10-28
Proton
p+
1+
1
1.67 × 10-24
Neutron
n0
0
1
1.67 × 10-24
Discovery of Electron
• resulted from scientists passing electric current
through gases to test conductivity
• used cathode-ray tubes
Scientists noticed that when current was passed through a glow
(or “ray”) was produced
Discovery of Electron
•
This led scientists to believe there were negatively
charged particles inside the cathode ray
Ions - an atom that has lost or gained
an electron(s)
The charge on an ion indicates an imbalance
between protons and electrons.
If the atom GAINS electrons it will have a
negative charge. (more e- than p+)
they are “takers”
If the atom LOSES electrons it will have a
positive charge. (more p+ than e-)
they are “givers”
Isotopes - atoms of the same element that
have the same # p+, but different mass
numbers.
Isotopes have different masses because they
have a different number of neutrons.
Boron
5
B
10.811
atomic number
(average) atomic mass
The average atomic mass - weighted average of
all the naturally occurring isotopes of an
element.
Example:
A sample of cesium is 75% 133Cs, 20% 132Cs and
5% 134Cs. What is the average atomic mass?
Answer:
.75 x 133 = 99.75
.20 x 132 = 26.4
.05 x 134 = 6.7
132.85 = average atomic mass
Beanium Lab
Average mass = mass (of that “isotope”or bean type)
# of pieces of that bean
% abundance = # of pieces of that bean × 100
Total # of pieces of bean