2. ATOMIC COMPOSITION
• Protons (p+)
– + electrical charge
– mass = 1.672623 x 10-24 g
– relative mass = 1.007 atomic mass units
(amu) but we can round to 1
• Electrons (e-)
– negative electrical charge
– relative mass = 0.0005 amu
but we can round to 0
• Neutrons (no)
– no electrical charge
– mass = 1.009 amu but we can round to 1
3. Atomic Number, Z
All atoms of the same element have
the same number of protons in the
nucleus, Z
13
Al
26.981
Atomic number
Atom symbol
AVERAGE Atomic Mass
4. Mass Number, A
• Mass Number (A)
= # protons + # neutrons
• NOT on the periodic table…(it is the AVERAGE
atomic mass on the table)
• A boron atom can have
A = 5 p + 5 n = 10 amu
A
Z
10
5
B
5. Atomic Symbols
Show the mass number and atomic number in
nuclear symbol form
mass number
23 Na
atomic number 11
6. Counting Protons, Neutrons, and
Electrons
• Protons: Atomic Number (from periodic table)
• Neutrons: Mass Number minus the number of
protons (mass number is protons and neutrons
because the mass of electrons is negligible)
• Electrons:
– If it’s an atom, the protons and electrons must be the SAME
so that it is has a net charge of zero (equal numbers of + and
-)
– If it does NOT have an equal number of electrons, it is not
an atom, it is an ION. For each negative charge, add an
extra electron. For each positive charge, subtract an
electron (Don’t add a proton!!! That changes the element!)
7. Isotopes
• Atoms of the same element (same Z) but
different mass number (A).
• Boron-10 (10B) has 5 p and 5 n
• Boron-11 (11B) has 5 p and 6 n
10B
11B
9. AVERAGE
ATOMIC MASS
• Because of the existence of isotopes, the mass of a
collection of atoms has an average value.
• Boron is 20% 10B and 80% 11B. That is, 11B is 80
percent abundant on earth.
• For boron atomic weight
= 0.20 (10 amu) + 0.80 (11 amu) = 10.8 amu
10B
11B
10. • 1895 – discovered how to use electromagnetic
radiation to create x-rays
• Led to significant advances in medicine,
especially on the battlefields of World War I
• In the 1900’s the damaging qualities of x-rays
were studied and proven useful in fighting some
cancers.
The first x-ray of
Roentgen’s
wife’s hand
11. Radiation was discovered purely by chance ……….
He put a couple of photographic
plates in a drawer next to a rock.
Days later he discovered that the
plates had patches on them where
they had been developed.
WHAT DO YOU BELIEVE HAPPENED HERE?
The “rock” in his desk contained URANIUM in it.
Becquerel discovered that it gave off invisible rays which
developed the film plates.
12. • Defined and studied radioactivity
• Trained by her father, worked with her
husband Pierre
• Isolated polonium and radium
• Nobel Prize for Physics and Chemistry
• Died of leukemia after never receiving
financial gain from her work
• Oldest daughter, Irene continued work and
earned Nobel Prize in Chemistry
13. All nuclear energy begins in the area of the atom called
the ……
The central “core” of the atom.
Contains PROTONS and
NEUTRONS.
Reactions that involve the nucleus
of an atom are called NUCLEAR
REACTIONS, and produce a
tremendous amount of energy.
14. THERE ARE THREE TYPES OF PARTICLES AND
ENERGY GIVEN OFF BY RADIOACTIVE ELEMENTS
1.ALPHA PARTICLES
-
Type of radiation where the
particles possess a positive
charge, cannot even penetrate
paper, has the most mass, and
moves slowly.
If you could see an alpha particle, it would look just like a helium
nucleus. Two protons, two neutrons.
15. THERE ARE THREE TYPES OF PARTICLES AND
ENERGY GIVEN OFF BY RADIOACTIVE ELEMENTS
BETA PARTICLES -
Type of radiation where the
particles have a negative
charge, penetrates living tissue,
and has less mass but moves
quicker than an alpha particle.
If you could actually see a beta particle it would appear
to be one “free” electron capable of moving anywhere.
16. THERE ARE THREE TYPES OF PARTICLES AND
ENERGY GIVEN OFF BY RADIOACTIVE ELEMENTS
GAMMA RAYS -
The only type of radiation which is
“energy” instead of particles.
Travels at the speed of light, has
no mass, is neutral in charge, and
penetrates just about every
substance. POWERFUL!!!!!!
Since Gamma rays are energy only and travel so
quickly, you would not see them even if you could!
17. The time it takes for 1/2 of a radioactive element
to decay. Every radioactive element has a unique
half-life. (some are in seconds and some are
billions of years!)
On the island of Bikini Atoll, scientists
back in the 1950’s tested nuclear
bombs for the government. Today,
nobody is still allowed to return there
because it is STILL RADIOACTIVE!!
18. Half-life formula:
Amount remaining = (initial amount) (1/2) n
Where n is number of half-lives.
If you need to find the number of half-lives that have
passed,
elapsed time
Number of half-lives (n) = half-life
