Download Nuclear Physics Rutherford`s model of the atom

Nuclear Physics
Rutherford’s model of the atom- Developed in 1911 by Ernest Rutherford after he found out the atom
consisted of subatomic particles called “protons” and “Electrons”. Nevertheless, it was not understood
where these particles were located in the atom. J.J. Thompson developed an idea that the protons moved
around freely with electrons, this was called “Plum Pudding Model”. Rutherford tested this with J.J.
Thompsons “gold foil” experiment. Rutherford then developed a planetary model of the atom where all
the electrons rotate around the protons in nucleus.
Bohr’s model of the atom- Developed in 1915 by Niels Bohr. Bohr’s model of the atom is a
modification of Rutherford’s model of the atom in 1911; it’s based on quantum mechanics and contains a
few errors. Still, it includes features of atomic theory without requiring strong math skills. Also, the Bohr
model explains the Rydberg formula and shows the amount of electrons per shell.
Proton- A stable subatomic particle occurring in all atomic nuclei, with a positive electric charge equal in
magnitude to that of an electron.
location: The nucleus.
Neutron- A subatomic particle of about the same mass as a proton but without an electric charge, present
in all atomic nuclei except those of ordinary hydrogen.
location: The nucleus.
Electron (negatron)-A stable subatomic particle with a charge of negative electricity, found in all atoms
and acting as the primary carrier of electricity in solids.
location: Orbiting around the nucleus.
Atomic Number: Equal to the number of protons in the nucleus of
the atom. All atoms have unique atomic numbers; we use these
numbers/values to determine the specific element the atom is. The
atomic number is found above the elemental symbol.
E.g. Helium’s atomic number is 2. Helium is found on right side of
the periodic table of elements.
Atomic Mass: The total mass of the protons, neutrons and electrons
in a single atom. About 99% of atoms mass are in its nucleus; in
essence the mass is the measurement of the nucleus. The mass on elements are found just below the
element symbol.
E.g. Helium’s atomic mass is 4.003.
Ions: An electrically charged atom(s) created by gaining or losing an electron. If an electron is lost the
atom becomes a “cation” (positive ion), metallic elements form cations. If an electron is gained it will
form an “anion” (negative ion), non-metallic elements will form anoins.
Isotopes: Atoms have the same number of protons but varying numbers of neutrons. There are 275
isotopes. The word “isotope” is formed from the Greek roots” “isos” and “topcos”, mean “Same place”.
Radio-isotopes: A chemical element that has an unpredictable nucleus and expels radiation during its
decay to a stable form. Radio-isotopes are very useful and used in many medical
Common Isotopes and Applications:
Most abundant non
Element
radioactive isotopes mass Radioisotope
number
Hydrogen
1,2
Tritium(3)
Oxygen
16
18(not radioactive)
Carbon
12
14
Phosphorus 31
32
Sulfur
32,33,34
35
Cobalt
59
60
Halflife Uses
12.4
years
Tracers for metabolic studies.
Metabolic studies and determining
--------- temperatures of ancient seas by
O16/O18 ratios.
5,745
Metabolic studies and dating recent
years
archeological artifacts.
14.3
Metabolic and Ecological tracer.
Days
Studies of nucleotides, nucleic acids.
87.9
Labeling proteins
days
Cancer therapy, source of gamma
5.3 years
rays
3 Types of Atomic Decay
Alpha: Atomic decay (alpha) is where the nucleus emits an alpha particle (2 protons & 2
neutrons) which “decays” the atom into one with 4 less atomic mass and a decreased 2 in
the atomic number.
(Alpha Decay Formula)
Beta:
Atomic decay (beta) is where the nucleus emits an electron or a positron 1.
Beta decay is a process which allows the atom to obtain the optimal ratio of protons and
neutrons. There are two types of beta decay: beta minus and beta plus. In the case of beta
decay that produces an electron emission, it is referred to as beta minus (β−), while in the
case of a positron emission as beta plus (β+).
Beta - :
Beta negative is where a neutron falls apart and becomes a proton and an
electron. At this point the proton stays in the nucleus but the beta particle (the
electron) is ejected from the nucleus. In order to still have conservation laws
obeyed, a very small, neutral particle must also be emitted from the nucleus.
That particle is called an antineutrino.
(Beta Negative Decay Formula)
Beta + :
Beta positive is where a proton decaying into a neutron and a positron, while also
releasing a neutrino, this is exactly opposite to beta negative.
(Beta Positive Decay Formula)
Gamma: Atomic decay (gamma) is where the nucleus emits a gamma ray which can lead to
nuclear fission or fusion. This happens most often after alpha or beta decay, this is due to
the fact that the atom has just had so much happen, it is in an unstable state. The particle
requires some form of energy release; it does this by releasing a bit of gamma radiation.
(Gamma Decay Formula)
Half Life: The time needed for half the nuclei in a sample of a given substance to experience radioactive
decay. The substance does not equal half of its full duration of radioactive decay. E.g. if one starts with
100 grams of radium 229, whose half-life is 4 minutes, then after 4 minutes only 50 grams of radium will
be left in the sample, after 8 minutes 25 grams will be left, after 12 minutes 12.5 grams will be left etc.
1 The positron or antielectron is the antiparticle or the antimatter counterpart of the electron. The positron has an
electric charge of +1e, a spin of ½, and has the same mass as an electron.
Nuclear Fusion
Nuclear Fission
-
The action of fusing 2 small atoms into one
larger one
-
The action of splitting an atom into 2
smaller ones
-
Occurs in stars, such as the sun
-
Does not normally occur in nature
-
Few highly radioactive particles are
released
-
Many highly radioactive particles are
released
-
Takes extremely large quantities of energy
in order to over to overcome electrostatic
repulsion
-
Takes very little energy to accomplish
-
The energy released by fusion is three to
four times greater than the energy released
by fission
-
In a nuclear plant fission makes a large
amount of chemical by-product and has a
chance of melting down
-
-
The energy released by fission is a million
times greater than that released in chemical
reactions
Fusion is much more costly than fission but
it produces almost no waste and has no
chance of melting down, but it is very
costly
Questions
1. When was Rutherford’s model of the atom developed?
a) 1911
b) 1809
c) 1909
d) 1900
2. When was Rutherford’s model of the atom improved by Bohr?
a) 1900
b) 1911
c) 1909
d) 1915
3. Where are neutrons located within the atom?
a) Nucleolus
b) Nucleus
c) Protons
d) Electrons
4. How many protons are released in alpha decay?
a) 4
b) 2
c) 7
d) 3
Write the corresponding number for each term. (6 marks)
Atomic mass ___
e
Atomic number ___
e
Half-life
___
1. The time needed for half the nuclei in a sample of a given substance to
experience radioactive decay.
2. A stable subatomic particle occurring in all atomic nuclei, with a positive
electric charge.
3. The antiparticle or the antimatter counterpart of the electron.
Isotopes
___
4. Equal to the number of protons in the nucleus of the atom.
Proton
___
5. Atoms have the same number of protons but varying numbers of neutrons.
Positron
___
6. The total mass of the protons, neutrons and electrons in a single atom.
Bonus:
List the amount of electrons per shell in the first 4 shells.
Answers:
1. A)
2. D)
3. B)
4. B)
Atomic mass 6
Atomic number 4
Half-life 1
Isotopes 5
Proton 2
Positron 3
Bonus:
Shell 1: 2
Shell 2: 8
Shell 3: 18
Shell 4: 18