THE ATOM

Smallest part of an element that has all of the properties of that

element.

HISTORY

Greeks and matter

John Dalton’s atom

Dmitri Mendeleev

Earth, wind, water, air and fire

Matter classified by atomic mass Hook and eye Elements composed of identical atoms

reacted in the same way

Arranged atoms in order of increasing mass.

Designed 1st periodic table (modern table arranges elements that

react the same chemically)

History cont.

Thomson’s atom

Ernest Rutherford

Neils Bohr

Plum pudding Electrons are negative (plums) Pudding is positive

Placed the nucleus in the center Nucleus had a positive charge

Atom is a mini solar system

Questions for you

What do particle accelerators do?

AMU is the acronym for

Smallest part of an element is a

Smallest part of a compound is a

Fundamental parts of the atom are

Atomic mass number for an electron is

What are the two types of nucleonsWhich of the fundamental particles is

heaviest?Which has a positive charge?Which is electrically neutral?Nucleons are ______times the mass of an

electronWhich particle ultimately determines the

chemical behavior of an atom?

A neutral atom has the _____number of electrons in orbits as protons in the nucleus

K L M N O P Q

Electron Arrangement

Review of the Periodic TableThe outermost shell is identified by the period

and the number of electrons in the outermost shell is identified by the group

Shell number –n- AKA Principle Quantum Number 2n2

Atoms with filled outer shells are stableNumber of electrons in outer shell determines

the chemical reaction

Transitional Elements

Fourth periodElectrons are added to inner shellsChemical properties of transitional

elements are dependent on number of electrons in the TWO OUTERMOST SHELLS

CENTIFUGAL FORCE

FLYING OUT INTO SPACE

CENTRIPETAL FORCE

PULLING INTO THE CENTER

Electrostatic attractionOpposites charges attractEbThe closer the electron is to the nucleus,

the stronger the Eb.EbThe greater the number of electrons, the

more tightly they are bound

THEREFORE

The larger the atom, the higher the electron binding energy

We can now deduce

More electrons mean higher atomic number because

The number of electrons = the number of protons and atomic number is determined by the number of protons

In Radiography

Tungsten is used to construct the anode and cathode because it has a high atomic number

A high atomic number means more energy is required to ionize the material

Recall that ionization causes eventual breakdown of material

Radioactivity

What determines if a nucleus of an atom is unstable?

Too many or too few neutrons

Radioactivity

Nucleus is unstableIn an attempt to become stable, emits

particles and energyThis is called radioactive decay or

disintegrationAtoms are called radionuclide

Alpha

Loses 2 units of positive charge

Loses 4 units of massEmits gamma raysHigh QFHigh LET

Beta

Neutrons converts to a proton

Electron type of particle is ejected

Increases the atomic number by one

Emits gamma rays

IONIZATING RADIATION AGAIN!!!!!

AlphaEmitted only from nuclei

of heavy elements (helium)

Travel quickly thru matter Ionization is quickHarmless if deposited

outside of body Inside it can completely

irradiate soft tissue

BetaLonger range than AlphaOriginate from the nuclei

of radioactive atoms.

See figure 4-18, pg 56

Radioactive half life

Time needed for a radioisotope to disintegrate into a stable atom

Period of time for the radioactivity to be reduced to half its original value

Never reaches zero