Chemistry Nuclear Review Notes

Glanville 2013

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

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

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

5B

Atomic Symbols

Show the mass number and atomic number in

nuclear symbol form

mass number23 Na

atomic number 11

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!)

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

Figure 3.10: Two isotopes of sodium.

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

• 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

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.

• 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

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.

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.

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.

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!

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!!

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