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Bahan Matrikulasi
Fisika (III): Fisika Inti

Oleh

Dedi Setiabudidaya

Program Studi Pengelolaan Lingkungan

Program Pascasarjana Universitas Sriwijaya

Periodic Table of the Elements



What is an atom?What are the parts of an atom?How do we see the parts of the atom?What is the structure of the atom?
Some questions about the atom



Atoms the historical view
The Greek Empedocle (around 492-432 BC.) divided matter into four elements, that he also called "roots": earth, air, fire and waterThe word "atom" comes from the greek "a-tomos" and signifies "indivisible". This notion was invented by Leucippe of Milet in 420 BC


In ancient times, many elements were known, including C, S, Cu, Ag, Au, Fe, Sn, Sb and Pb. The names of most of these are from the Latin words.From 1000-1869, about 50 additional elements were discovered, many by alchemists, including As, Zn, P, Pt, Ni, N, O, Cl and Al.Mendeleyevs periodic table (1869) classified and sorted elements based on common chemical properties. His table had 62 known elements, and left space for 20 elements that were not yet discovered. The elements were arranged in order of atomic number.


The electron was discovered in 1897 by Thomson. He imagined the atom as a raisin pudding with electrons stuck in a cake of positive chargeIn 1912, Rutherford discovered the nucleus by doing scattering experiments. He concluded the atom was mostly empty space, with a large dense body at the center, and electrons which orbited the nucleus like planets orbit the SunRutherford also realized that the nucleus must contain both neutral and positively charged particles. The neutron was then discovered in 1932 by Chadwick.


Following Rutherfords planetary model of the atom, it was realized that the attraction between the electrons and the protons should make the atom unstableBohr proposed a model in which the electrons would stably occupy fixed orbits, as long as these orbits had special quantized locationsIn the Bohr model, the electron can change orbits, accompanied by the absorption or emission of a photon of a specific color of light. Modern quantum theories lead to stable locations of electrons, which are not exact planetary orbits, but are characterized by specific quantum numbers.


Each electron shell is characterized by a different principle quantum number, usually called n.


In quantum theory, the electron shells are not fixed orbits, but clouds of probability. You cant measure the exact location of the electron.
Each electron orbital has a different shape, and no two electrons can be in the same orbital (unless they have opposite spins.)
The quantum rules for the electron orbitals in an atom determine the row structure in the periodic table. The geometry of the electron orbitals determines the structure of an atom


The spin of the electron is another quantum property. In the planetary model, it is similar to the spin of the Earth on its axis. There are two choices for the orientation of the electrons spin axis: up or down.


Some questions:
What is an element?Why are nuclei and atoms stable?What is a molecule?


Atom: smallest unit of an elementElement: any of more than 100 fundamental substances that consist of atoms of only one kindMolecule: a collection of atoms, bound together.Molecules can be made from only one element, such as H2 or O2Molecules can be made from different elements, such as H2O or CO2


Parts of an Atom
Each element in the Periodic Table has a different number of protons in its nucleusProtons have positive chargeChange the number of protons change elements This is called nuclear physics The element also has the same number of electronsElectrons have negative chargeChange the number of electrons ionize the element This is called chemistry Some elements also have neutrons Neutrons have no chargeThey are in the nuclei of atoms


The Hydrogen Atom

One electron orbiting a nucleus

1 proton = Z = atomic number

0 neutrons = N

Total mass = A = Z+N =1

Singly ionized Hydrogen is missing one electron = 1H+

Add a neutron and you have Deuterium = 2H = D

1H



p

e

The Helium Atom

Two electrons orbiting a nucleus

2 protons = Z = atomic number

2 neutrons = N

Total mass = A = Z+N =4

Singly ionized Helium is missing one electron = 4He+

Doubly ionized Helium is missing both electrons = a particle = 4He++



p

p

n

n

e

e

4He

Isotopes and Elements
If Helium loses one of its neutrons, it becomes an isotope
3He

3H (Tritium)
If Helium loses one of its protons (and one of its electrons), it becomes a different element


p

n

n

e

p

p

n

e

e

Radioactivity ("Activity")
Definition: A collection of unstable atoms that undergo spontaneous transformation that result in new elements. An atom with an unstable nucleus will decay until it becomes a stable atom, emitting radiation as it decaysSometimes a substance undergoes several radioactive decays before it reaches a stable stateThe amount of radioactivity (called activity) is given by the number of nuclear decays that occur per unit time (decays per minute).


Types of Radiation



Mass

(amu)

Charge

Travel Distance in Air

Alpha

Beta Plus

Beta Minus

Gamma

X-Rays

Neutron

4.0000

0.0005

0.0005

0.0000

0.0000

1.0000

+2

+1

-1

0

0

0

few centimeters

few meters

few meters

many meters

many meters

many meters

Interaction of Radiation with Matter
Radiation deposits small amounts of energy, or "heat" in matteralters atomschanges moleculesdamage cells & DNAsimilar effects may occur from chemicalsMuch of the resulting damage is from the production of ion pairs


Exposure and Dose
Exposure is ionization in air and is measured in Roentgen (R) or coulomb/kg (C/kg)1 R = 2.58 10-4 C/kgAbsorbed dose is the energy absorbed by a material and is measured in rad or gray (Gy)1 rad = 100 erg/g1 gray = 1 joule/kg1 gray = 100 rad1 rad (in air) = 0.87 R


Dosimetry System
Dose equivalent (H) is a measure of the biological damage caused by radiationH = D Q N
D = absorbed dose (in a tissue or organ)

Q = quality factor

(Q for and = 1, Q for = 20)

N = other modifying factors (N = 1)
Dose equivalent measured in rem or sievert (Sv)


Dosimetry System
Effective dose equivalent (He)
He = wT HT

HT = Dose equivalent in tissue or organ T

wT = Weighting factor for tissue or organ T
wT used to account for the different sensitivities of tissues and organs to radiationEffective dose equivalent also measured in rem or sievert (Sv)



TissuewTGonads0.25Breast0.15Red bone marrow0.12Lung0.12Thyroid0.03Bone surfaces0.03Remainder0.30



Absorbed

Dose (Rads)

Effect

10,000

1,200

600

450

100

50

25

5

Death in a few hours

Death within days

Death within weeks

LD 50/30

Probable Recovery

No observable effect

Blood changes definite

1st Blood change obs

Annual Dose from Background Radiation (US)



Total US average dose equivalent = 360 mrem/year

Radon

Internal 11%

Cosmic 8%

Terrestrial 6%

Man-Made 18%

55.0%

Medical X-Rays

Nuclear

Medicine 4%

Consumer

Products 3%

Other 1%

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