Bellringer:Potassium has two naturally

occurring isotopes. potassium—39 has a mass of 38.964 amu and potassium—41 has a mass of 40.962 amu. The atomic mass of potassium is 39.098 amu. What is the % abundance of both isotopes?

potassium—39 has a mass of 38.964 amu

potassium—41 has a mass of 40.962 amu

Atomic mass 39.098 amu

Two isotopes abundance must equal 1 or the two isotopes % abundance must equal 100%x+y = 1 therefore y=1-x

39.098amu=38.964amu(x) + 40.962amu(1-x)

RadioactivityOne of the pieces of evidence

for the fact that atoms are made of smaller particles came from the work of ________ (1876-1934).

She discovered ________, the spontaneous disintegration of some elements into smaller pieces.

RadioactivityIt is not uncommon for some

isotopes of an element to be unstable, or radioactive.

We refer to these as radioisotopes.There are several ways

radioisotopes can decay and give off energy known as radiation.

Nuclear Reactions vs. Normal Chemical

ChangesNuclear reactions involve the

nucleus

The nucleus opens, and protons and neutrons are rearranged

The opening of the nucleus releases a tremendous amount of energy that holds the nucleus together – called binding energy

“Normal” Chemical Reactions involve electrons, not protons and neutrons

The Nucleus

Remember that the nucleus is comprised of the two nucleons, protons and neutrons.

The number of protons is the atomic number.

The number of protons and neutrons together is effectively the mass of the atom.

Isotopes

Not all atoms of the same element have the same mass due to different numbers of neutrons in those atoms.

There are three naturally occurring isotopes of uranium:Uranium-234Uranium-235*Uranium-238

Types of Radioactive Decay Alpha Decay

Loss of an -particle (a helium nucleus)

He42

U23892 Th234

90 He42+

Types of Radioactive Decay Beta Decay

Loss of a -particle (a high energy electron)

0−1 e0

−1or

I13153 Xe131

54 + e0−1

Types of Radioactive Decay Gamma Emission

Loss of a -ray (high-energy radiation that almost always accompanies the loss of a nuclear particle)

00

Types of Radiation

e01

He42

• Alpha (ά) – a positively charged helium isotope - we usually ignore the charge because it involves electrons, not protons and neutrons

•Beta (β) – an electron

•Gamma (γ) – pure energy; called a ray rather than a particle

Penetrating Ability

Nuclear ReactionsAlpha emission

Note that mass number goes down by 4 and atomic number goes down by 2.

Nucleons (nuclear particles… protons and neutrons) are rearranged but conserved

Nuclear ReactionsBeta emission

Note that mass number is unchanged and atomic number goes up by 1.

Write Nuclear Equations!Write the nuclear equation for the

alpha decay of radon-222222Rn 218Po + 4He

Write the nuclear equation for the beta emitter Co-60.

60Co 60Ni + 0e

8486 2

27 28 -1