The Atom

What’s Inside an Atom?• An atom is made up of a team of three

players: protons, neutrons, and electrons

• They each have a charge, mass, and a location

• Protons + Neutrons collectively called nucleons

What is the structure of an atom?

• Nucleus – center of the atom– Home of Protons and Neutrons

–Proton• Has a positive (+) charge• Has a relative mass of 1• Determines the atomic number• Found inside the nucleus

What is the structure of an atom?

– Neutron

• Has no charge (0)

• Has a relative mass of 1

• Determines the isotope

–Isotopes are two of the same element with different masses

• Found inside the nucleus

What is the structure of an atom?• Electron

– Has a negative (-) charge

– Has a relative mass of 0 (zero)

– Determines the ion

– Found outside the nucleus

Electrons circle around the nucleus of an atom.

Protons are a main part of the nucleus of an atom.Neutrons also hang out in the nucleus of an atom.

Electrons have a negative charge. Protons have a positive charge. +Neutrons have no charge. 0

Electrons are little and have a mass of almost zero.Protons are big and have a mass of one.Neutrons are also big and have a mass of one.

How are P, N, e- related?

• # protons = atomic number = Z

• # electrons = # protons in a neutral atom

• # protons + # neutrons = mass number = A

– Ex: The atomic number of Hydrogen (H) is 1, so all hydrogen atoms have 1 proton.

– Ex: All Oxygen atoms (O) have 8 protons, so the atomic number of Oxygen is 8.

• Remember all atoms are electrically neutral.• Therefore; the number of Protons equal the number of

Electrons.• Meaning the number of negatively charged particles

must equal the number of postively charged particles.

– Ex: Helium (He) has 2 protons and 2 neutrons: its mass number is 4.

– Ex: Carbon (C) has 6 protons and 6 neutrons: its mass number is12.

A XZ N

• # protons + # neutrons = mass number = A

•# protons = atomic number = Z

•# neutrons

Structure of the Nucleus

AAl

13 14

27

Structure of the Nucleus

• The ratio of the number of neutrons to the number of protons N/Z is an approimate index of the stability of a nuclide.

• N/Z = 1 in the stable nuclei with low atomic no.

• Ex, C6

12

Structure of the Nucleus

Nomenclature • Isotopes:• Nuclides of the same atomic number. O O O

• Isotones:• Nuclides having the same number of neutrons but different atomic

number

• Fe Co Cu

• Isobars:• Nuclides with the same no. of nucleons that is the same mass no. but

different no. of protons

• Cu Zn

• Isomers:• Nuclides having the same number of protons and neutrons but differing

in energy states and spins. 99Tc 99mTc

815

816

817

2659 60 62

27 29

67673029

Units of Radioactivity• 1 curie (Ci) = 3.7 X 10 10 dps • = 2.22 X 10 12 dpm• 1 millicurie (µCi) = 3.7 X 10 7 dps • = 2.22 X 10 9 dpm• 1 microcurie (µCi) = 3.7 X 10 4 dps • = 2.22 X 10 6 dpm

• 1 Becquerel (Bq)= 1 dps = 2.7 X 10 -11 Curie• 1 kilobecquerel (Bq)= 2.7 X 10 -8 Curie

• 1 Ci = 3.7 X 10 10 Becquerel (Bq)

Units of Radioactivity

Decay Equations

• -dN/dt=YN– Y Lambda= decay constant. – Defined as the probability of disintegration per unit

time for the radioactive atom– -dN/dt = A =disintegration rate – N is the no. of radioactive atoms

• At = Aoe-yt

• A=yN• Y=0693/t1/2

– t1/2 = the time required to reduce the intial activity of a radionuclide to one half

Problems

1. At 11:00 A.M., the 99mTc readioactivity was measured as 9 mCi on a certain day. What was the activity at 8:00 A.M. and 4:00 P.M. on he same day (t1/2 of 99mTc= 6hr)

Thank You

“Instead of giving yourself reasons why you can’t ,

give yourself reasons why you can”