Transcript Atomic structure and the nucleusstud

Chemistry
Chapter 3
Atomic Structure and
the Nucleus
World of Chemistry
Zumdahl
Last revision Fall 2008
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Structure of the atom
We have all learned from an early age that
the atom is composed of 3 tiny particles
Particle
Symbol
Relative
Electric
Charge
Actual Mass
(g)
Relative Mass
Electron
Proton
Neutron
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And the atom has 2 main regions:
the nucleus and the electron cloud.
The periodic table can help us figure out the
protons, neutrons and electrons for any element
In a neutral
atom e- = p+
ep+
no
Nucleus
Electron
Cloud
19
K
Potassium
39.098
Atomic number: This
tells the number of
protons for the element
Symbol: The symbol
always starts with a
capital letter
Name
Average Atomic Mass:
When this number is rounded to
a whole number it becomes the
Mass Number which is the total
particles in the nucleus
This is the average
abundance of isotopes
occurring in nature
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Determining number of
particles in an atom



Protons = the atomic number of the element.
The protons identify the atom
Electrons = as long as the atom is neutral,
electrons are equal to protons.
Neutrons = the mass number tells
19
the total particles in the nucleus
so just subtract the atomic number
from the mass number.
Potassium
39 – 19p+ = 20 no
39.098
K
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Isotopes: an element with
various masses.
This indicates the mass number of the element
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Symbolic notation for atoms,
ions and isotopes
Mass number 
Atomic number 
39
K
19
+
The charge implies
electrons have been
gained or lost and the
atom is now an ion
 Element Symbol
This is also known as the complete chemical symbol
or it can be written as an isotopic name:
Potassium-39
 Mass number
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Atomic Masses
Elements occur in nature as mixtures of isotopes
Carbon =98.89% 12C
1.11% 13C
<0.01% 14C
How can you represent all the isotopes in one mass
value? Remember, any given sample can have this abundance of isotopes.
1. Multiply the abundance of the element by the element’s mass
2. Add the masses and divide by 100
Carbon atomic mass = 12.01 amu
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In the beginning…




The big bang many particles were created and
they would randomly collide and stick
together.
What if two protons came together?
Neutrons are added as glue for the nucleus.
If the balance of protons to neutrons (not
always equal numbers) was not right the
nucleus becomes unstable and radioactive and
begins to spit off particles and/or energy to
achieve a balance.
These emissions are called radiation
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
Three Kinds of Nuclear
Radiation



Alpha decay: An alpha particle
or helium nucleus is emitted
from the nucleus.
Beta decay: A beta particle or
electron from the decay of a
neutron is emitted from the
nucleus.
Gamma decay: A burst of
gamma electromagnetic
radiation is emitted from the
nucleus.
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Alpha Particles α



Alpha particles contain 2p+ and 2n0 just
like a helium nucleus.
It’s a big particle compared to others and
carries the lowest energy of the three.
This kind of radiation can be blocked by
paper or clothes.
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Beta Particle β



A Beta is an electron that is released from the
nucleus.
The electron comes from a neutron decaying. It
breaks apart into a proton and an electron.
The electron leaves and the proton stays
behind.
Beta radiation has more energy than alpha and
needs at least 1 cm of aluminum or similar
material to stop the radiation.
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Gamma Radiation γ



Gamma radiation is an electromagnetic wave
with a very short wavelength and a very high
frequency.
It has very high energy.
You would need 6 ft of concrete or 6 inches of
lead to stop gamma rays.
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Nuclear Reactions
The nuclei can interact in two ways
1. Fusion : Two nuclei come together
and fuse to make a bigger nucleus.
2. Fission : A large nucleus breaks
apart and makes two or more
smaller nuclei.
Both interactions
create large
amounts of Energy!!!!
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