Download Structure of the Atom

Structure of the
Atom
Dr. Kamal Omer, Associate Professor of
Biochemistry & Molecular Biology
Physical and Chemical sciences
alone may not completely explain
the nature of life, but they at least
provide the essential framework
for such an explanation.
Thus, for understanding of
nature of life all students of
Health Sciences must have a
fundamental understanding of
organic chemistry and
biochemistry.
Organic chemistry is the study of
Carbon compounds.
Organic compounds, are
compounds composed primarily
of a carbon skeleton.
• All living things are composed of
organic compounds.
• The atom is the fundamental
component of all chemical
substances including the
protoplasm (the living
substance).
• Atoms have mass and space
thus, they are matter.
The name atom comes from the Greek
word ἄτομος (atomos, "indivisible")
from ἀ- (a-, "not") and τέμνω (temnō,
"I cut"), which means indivisible,
something that cannot be divided
further.
The concept of an atom as an indivisible
component of matter was first
proposed by early Indian and Greek
philosophers.
th
18
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19
In the
and
centuries,
chemists provided a physical basis
for this idea by showing that
certain substances could not be
further broken down by chemical
methods, and they applied the
ancient philosophical name of
atom to the chemical entity.
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19
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20
During the late
and early
centuries, physicists discovered
sub-atomic components and
structure inside the atom,
thereby demonstrating that the
chemical "atom" was divisible
and that the name might not be
appropriate. However, the name
atom was retained.
An atom is one of the basic units of
matter. Atoms form the building
blocks of the simplest substances,
the chemical elements. Nearly
everything on earth is made up of
atoms. Each element consists of
one basic kind of atom.
• Protoplasm, the living
substance of cells is termed
living matter.
• Understanding of the atom is
essential for the understanding
the nature of protoplasm.
1. Methane 2. DNA
1. Methane with 1
Carbon atom
3. Glucose
2. DNA with tens of
Billions of Carbon atoms
• Atom is very very small, less than
billionth of an inch in diameter.
• Atoms have sizes on the order of
1-5 A (1 angstrom = 10-10 m) and
masses on the order of 1-300
atomic mass unit (amu).
• Thus, an atom can’t be seen with
light microscope.
This unit is much more convenient
to use than grams for describing
masses of atoms. It is defined so
that both protons and neutrons
have a mass of approximately 1
amu.
Physical nature of atoms is
complex, its structure is
similar to the solar system
in which several planets
continuously circle around
the sun in certain orbits.
Most atoms consist of three basic
particles: protons (with a
positive electrical charge),
electrons (with a negative
electrical charge), and neutrons
(with no electrical charge)
Protons and neutrons are bundled
together in the center of the atom,
called the nucleus. The electrons
move around the nucleus, each in its
own orbit like the moon around the
earth.
Each atom of the same element is
characterized by a certain number of
protons in the nucleus.
• This atomic number identifies the
elements. The list of elements
(ranked according to an
increasing number of protons) is
called the Periodic Table.
• Protons and neutrons are held together rather
closely in the center of the atom. Together
they make up the nucleus, which accounts for
nearly all of the mass of the atom.
• Electrons move rapidly around the nucleus
and constitute almost the entire volume of
the atom. Although quantum mechanics are
necessary to explain the motion of an electron
about the nucleus, we can say that the
distribution of electrons about an atom is
such that the atom has a spherical shape.
• An atom is similar to the solar system
consists of one or more electrons.
• Electrons like planets orbiting a
nucleus (like the sun).
• Orbiting electrons are arranged in
regular sequence, each in its own
shell. Atoms in the protoplasm are
different and are called elements (eg.
hydrogen, oxygen, nitrogen,
phosphorous).
• The nucleus contains a definite
number of protons & neutrons.
• The interaction of electrons,
protons & neutrons gives each
atom its distinctive chemical
properties.
• Even though the number of protons in the
nucleus is the same for all atoms of a
particular element, the number of neutrons
in the nucleus can differ for different atoms
of the same element. Atoms of an element
that contain the same number of protons,
but different numbers of neutrons, are called
isotopes of the element. Isotopes are
identified by adding the number of protons
and neutrons together, a number which is
referred to as the mass number.
• The number of electrons is equal
to the number of protons.
• e.g. H: 1e¯ & 1p⁺. O: 8e¯ & 8p⁺.
• Neutron is neutral.
• The atom is electrically neutral.
When an atom loses an (e¯) it
becomes positive charged (cation)
& when it gains an e¯ it becomes
negatively charged (anion). Cations
& anions are called ions.
• The electrons of an atom are
bound to the nucleus by the
electromagnetic force. Likewise, a
group of atoms can remain bound
to each other by chemical bonds
based on the same force, forming
a molecule.
Atomic number & atomic weight
The atomic number is equal to
the positive charges or the
number of electrons or to the
ordinal number of the element
in the periodic table.
• The atomic weight is equal to the
total number of protons &
neutrons.
The extra-nuclear electrons:
• Chemical substance depends on
interaction between the outer
extra-nuclear electrons of the
atoms combining together.
• The chemical properties of an
atom depend on the arrangement
of the extra-nuclear electrons.
• Eg. Each element in group one of
the Period. Table has one electron
in the outer most orbit.
• The total number of electrons
that can occupy any shell is given
by the formula 2n². n is the
principal quantum number
(KLMNOPQ or 1-7). ie group:
• 1. Li 2. 1; Na 2.8.1; K 2.8.8.; Ag
2.8.18.18.1
• Group 2. Be 2.2; Mg 2.8.2; Ca
2.8.8.2.
An atom is classified according to
the number of protons and
neutrons in its nucleus: the
number of protons determines
the chemical element, and the
number of neutrons determines
the isotope of the element.
• A unit of mass called the atomic mass unit
(amu) is much more convenient to use than
grams for describing masses of atoms. It is
defined so that both protons and neutrons
have a mass of approximately 1 amu.
Protons and neutrons have almost the same
mass, while the electron is approximately
2000 times lighter. Protons and electrons
carry charges of equal magnitude, but
opposite charge. Neutrons carry no charge
(they are neutral).
• Chemical reactions involve either
the transfer or the sharing of
electrons between atoms.
Therefore, the chemical
reactivity/ properties of an
element are primarily dependent
upon the number of electrons in
an atom of that element.
• Protons also play a significant role
because the tendency for an atom to
either lose, gain or share electrons
are dependent upon the charge of
the nucleus. Therefore, we can say
that the chemical reactivity of an
atom is dependent upon the number
of electrons and protons, and
independent of the number of
neutrons.
• The mass and radioactive
properties of an atom are
dependent upon the number
of protons and neutrons in the
nucleus.
Atoms’ properties
• Combine with one another
through chemical bonds to form
molecules. e.g. the ions of Na⁺
and Cl⁻ form an ionic bond. The
result is NaCl (1 molecule).
• Water: H₂O (H-O-H covalent
bonds).
• Hydrogen bonds are formed
between molecules of water to
give clusters.
Extra-nuclear Electrons
Electrons are arranged around the
nucleus in different orbits.
Orbits have different energies.
• The transfer of electrons from one
orbit to an other leads to
absorption or emission of energy.
• Electrons rotate on their selected
orbits do not radiate energy
(stationary states, least energy).
• In any other state, the atom is
said to be excited.
• Various energy levels (orbits) are
labeled by quantum numbers.
These are:
1. The principle quantum Number:
(PQN) This is referred to stationary
or circular orbits (1-7; or K-Q )
the first one is that near to the
nucleus 1 or K.
• Each PQN represents a shell (a
group) of orbits.
• Total Number of electrons that can
occupy any shell is given by the
formula 2n². n is the PQN.
2. Subsidiary QN, which represents
the various orbits within a shell
(1,2,3,4 or s,p,d,f). The number of
SQN in any shell is limited.
3. Magnetic QN:
The L (2) PQN can contain a max.
of 8e¯. Two of them with
opposite spin↕ will be in 2S level.
The remaining 6e¯ are different
(the 2P orbits are divided into 3
levels, 2px, 2py & 2px).
3d into 3d₁-3d₅ (∑10e¯). The f
subsidiary orbit is divided into 7
levels.
• The subdivision of the SQNs into
3p, 5d & 7f is called MQN.
4. Spin QN:
Each 2e⁻ in any levels of 3d, 5p & 7f
rotate in opposite directions, this
refers to as spin QN
Thank You