Nuclear pharmacy lecture 1
Introduction
All substances are made of atoms.
These have electrons (e) around the outside (negatively
charged), and nucleus in the middle.
The nucleus consists of protons (positively charged) and
neutrons (neutral), collectively called nucleons.
 Protons are positively charged with a mass 1800 times that of
electrons.
 Neutrons have the same mass like protons but carry no charge.
The atom
 All matter is made up of elements (e.g. carbon, hydrogen,
etc.).
 The smallest part of an element is called an atom.
Atom of different elements contains different numbers of 
protons.
 The mass of an atom is almost entirely due to the number of
protons and neutrons.
The Atom
The atom consists of two parts:
1. The nucleus which contains:
Protons
Neutrons
2. Orbiting electrons
For an atom of a given element, the number of electrons moving around the
nucleus equals the number of protons, balancing the electrical charge of the
nucleus.
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 The electron configuration of the atom determines the
chemical properties of an element.
 The nuclear structure characterizes the stability and radioactive
decay of the nucleus of an atom.
The atom has a radius of approximately 10-8 cm, with the
nucleus having a radius of 10-12 cm.
→ The mass M of a nucleus is always less than the combined
masses of the nucleons A in the nucleus.
→ This difference in mass (M-A) is termed the ‟mass defect”,
which has been utilized as energy in binding all the nucleons in
the nucleus.
→ This energy is the ‟ binding energy” of the nucleus and
needs to be supplied to separate all nucleons completely from
each other.
→ The binding energy of an individual nucleon has a definite
value depending upon the shell it occupies, it is approximately
equal to the total binding energy divided by the number of
nucleons.
→ This energy is about 6 to 9 MeV and has to be supplied to
remove a single nucleon from the nucleus.
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Structure of the nucleus
Mass number = number of protons + number of neutrons
A
Z
Elemental atom
X
N
Neutron number
Atomic number = number of protons
Electronic structure of the Atom
 The electrons are located in discrete energy orbits or shells
around the nucleus (Bohr atomic theory).
 These energy shells, referred to as the K shell, L shell, N shell,
etc., are stationary and arranged in order of increasing energy.
 Each orbit has a limited capacity to hold only a definite
number of electrons. That K contains 2 electrons, L contains 8
electrons.
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► Each shell is designated by quantum number n, called the
principal quantum number.
► Each energy shell is subdivided into subshells or orbitals,
which are designated as s, p, d, f, etc. (azimuthal quantum
numbers, l).
l = 0,1,2……etc.
► The electron will enter the orbital of the lowest energy first
and the next higher energy orbital is then filled.
For example: 11Na
1s2 2s2 2p6 3s1
BOHR ATOM
electrons:
n = principal
quantum number
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n=3 2
Nucleus: Z = # protons
= 1 for hydrogen to 94 for plutonium
N = # neutrons
Atomic mass A ≈ Z + N
n labels shells; shells are composed of sub-shells: s, p, d, f, …
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The periodic table
 The periodic table is a chemistry reference.
 Elements are arranged left to right and top to bottom in order of
increasing atomic number.
 This order usually coincides with increasing atomic mass.
 The different rows of elements are called periods. Elements of each
row have the same number of energy levels (shells) but dissimilar
chemical properties.
The period number of an element signifies the highest energy level an
electron in that element occupies.
 The different columns of elements are called groups. Elements in the
same group have similar chemical properties.
Describe the Periodic Table
Atomic Mass:
The atomic mass is the average mass of an element in atomic mass units ("amu").
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Models for the arrangement of nucleons in a nucleus
1. Bohr liquid drop theory: The nucleus is assumed to be spherical and
composed of closely packed nucleons, and particle emission by the
nucleus resembles evaporation of molecules from a liquid drop.
2. In the shell model, nucleons are arranged in discrete energy shells
similar to the electron shells of the atom in the Bohr atomic theory.
Nuclei containing 2, 8, 20, 50, 82 or 126 protons or neutrons are very
stable and the nucleon numbers are called magic numbers.
3. Nuclei are less stable if they contain an odd number of protons or
neutrons, whereas nuclei with even numbers of protons and neutrons are
more stable.
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 The stability of the atom depends on the neutrons to protons
ratio (N/Z) ratio in the nucleus.
 This ratio equals 1 in the stable nuclei with a low atomic
number, such as 126C, 168O and 147N, and the ratio increases with
increasing the atomic number of the nucleus.
For example, this ratio is 1.40 for 12753I.
Electrons distribution
Valence electrons:
●● Electrons in the highest (outer) electron shell.
●● Have most contact with other atoms.
●● They are distributed as shared or bond pairs and unshared or lone
pairs.
Octet Rule:
● All chemical bond formation is governed by the octet rule that the
electronic structure of each atom in a chemical bond containing 8
electrons.
● An octet in the outer shell makes atoms stable.
● Electrons are lost, gained or shared to form an octet.
● Metals lose electrons to match the number of valence electrons of their
nearest noble gas e.g. He [2], neon [2,8]
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Octet Rule = atoms tend to gain, lose or share electrons so
as to have 8 electrons
Chemical bonds: an attempt to fill electron shells
1. Ionic bonds
2. Covalent bonds
3. Covalent coordinate
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1. IONIC BOND
- bond formed between two ions by the transfer of electrons.
- Ionic compounds result when metals react with nonmetals. - Produce
charged ions all states. Conductors and have high melting point.
Examples; NaCl, CaCl2
Ionic bond – electron from Na is transferred to Cl, this causes a
charge imbalance in each atom. The Na becomes (Na+) and the
Cl becomes (Cl-), charged particles or ions.
2. COVALENT BOND
- Bond formed by the sharing of electrons. It means that each of the
atoms participating in bond formation contributes one electron to the
bond.
- The shared electrons are localized in the region between the two
atoms and unlike to the ionic bonds, do not belong exclusively to one
atom alone.
- Stable non-ionizing molecules, they are not conductors at
any state.
Examples; O2, CO2, C2H6, H2O
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Covalent bonds: Two atoms share one or more pairs of outer-shell electrons.
A. Non-Polar covalent bond
When electrons are shared equally, for example H2 or Cl2
Oxygen Atom
Oxygen Atom
Oxygen Molecule (O2)
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B. Polar covalent bond
when electrons are shared but shared unequally, for example Hcl, H2O
- water is a polar molecule because oxygen is more
electronegative than hydrogen, and therefore electrons
are pulled closer to oxygen.
3. Coordinate covalent bond
The pair of electrons required for bond formation is donated by only one
atom to another that can accommodate two electrons in octet formation.
Nitrogen and oxygen atoms have donated their lone pair of electrons to a
hydrogen bond.
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In a coordination complex:
an arrow is used to show the bonding interaction of an electron
pair from a neutral ligand to an acceptor central atom.
[Co(H2O)6]2+ + 6 NH3 -----> [Co(NH3)6]2+ + 6 H2O
Ligand or complexing agent
2+
NH3
H3N
NH3
Co
NH3
H3N
Metal ion
NH3
Donation of unshared pair of electrons
Ethylene Diamine Tetraacetic Acid (EDTA)
Chelating agent
● Single ligand molecule can possess more than one donor atom and can
donate more than one pair of electrons in the complex.
● In such cases, more than one coordinate covalent bond is formed in the
complex. The mechanism of bond formation is called chelation.
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