Atomic structure refers to the organization and composition of atoms, which are the fundamental building blocks of matter. Atoms are incredibly small and consist of several subatomic particles, primarily protons, neutrons, and electrons. Understanding atomic structure is essential in the field of chemistry and forms the basis for our understanding of the physical and chemical properties of elements and compounds.

1. ATOMIC STRUCTURE
DR. MAAJID MOHI UD DIN MALIK
ASSISTANT PROFESSOR
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2. INTRODUCTION
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Atomic structure refers to the makeup and organization of
atoms, the basic building blocks of matter. Atoms are
composed of three main types of particles: protons, neutrons,
and electrons. The protons and neutrons are located in the
nucleus of the atom, while the electrons occupy energy levels
or orbitals that are arranged in shells around the nucleus.

3. CONTINUE
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The number of protons in an atom's nucleus, also known as its atomic
number, determines what element the atom is. For example, all atoms
with 6 protons in their nucleus are carbon atoms, while atoms with 8
protons are oxygen atoms. The number of neutrons in an atom's
nucleus can vary, leading to different isotopes of the same element.
Isotopes are atoms of the same element that have the same number of
protons but a different number of neutrons in the nucleus.

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The electrons in an atom occupy specific energy levels or orbitals, which are
arranged in shells around the nucleus. The first shell, also known as the K-shell,
can hold up to 2 electrons, the second shell, also known as the L-shell, can hold
up to 8 electrons, and the third shell, also known as the M-shell, can hold up to
18 electrons. The outermost shell is known as the valence shell, and the number
of electrons in this shell determines the chemical properties of the atom and its
ability to bond with other atoms.

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The behaviour of atoms and their electrons is described by quantum mechanics,
a branch of physics that deals with the behaviour of particles on a very small
scale. This theory explains phenomena such as electron spin and the shapes of
atomic orbitals. Electron spin is a fundamental property of electrons, which can
be thought of as a type of rotation. The shapes of atomic orbitals, which are the
regions of space where electrons are most likely to be found, can be described by
mathematical equations called wave functions.

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Furthermore, the arrangement of electrons in the orbitals of an
atom is known as its electron configuration. The electron
configuration of an atom can be determined by using the quantum
mechanical principle known as the Pauli exclusion principle, which
states that no two electrons in an atom can have the same set of
quantum numbers.

7. PERIODIC TABLE
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8. MATTER IS MADE OF ATOMS
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1. Hydrogen is the most common atom of our universe
2. Types of atoms in Earth’s Crust
1. Iron 5%, Aluminum 8%, Silicon 28%, Oxygen 47%, Other
12%
3. Types of atoms in Humans
1. Nitrogen 3%, Hydrogen 10%, Oxygen 61%, Other 26 %

9. NAME & SYMBOLS OF ELMENTS
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 Each element has its own symbol
 Some elements use the first letter of the name: hydrogen (H), Sulfur (S), Carbon
(C)
 Other elements use the first letter of the name plus another letter: aluminium
(Al), Platinum (Pt), Zinc (Zn)
 The first letter is always capitalized and the following letters are lowercase.

10. 400 B.C.
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Early Greek Philosophers determined that atoms
are the building blocks of matter.

11. JOHN DALTON (1766-1844)
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John Dalton’s theory of the atom
started out as a solid sphere with no
charges
Proposed the atomic theory by
investigating the atomic weights of
atoms

12. J.J THOMSON (1856-1940)
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.J.J Thomson determines that an atom is made up of negative
electrons embedded in a sea of positive charges
+
-
-
-
-
+
+
+

13. 1911
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Ernest Rutherford did some experiments with thin metal foils and found that
the positive charge is located within a central nucleus

14. 1913
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Niels Bohr worked under Rutherford but found problems with his theory. He
ultimately determined that Electrons are in circular orbits with increasing
energy levels.

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The modern atomic model shows that electrons occupy
regions of space whose shape is described by complex
mathematical equations. (James Chadwick)

16. HISTORY OF ATOMIC THEORY
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 John Dalton’s theory of the atom started out as a solid sphere
with no charges.
 Then J.J. Thomson figured out there were positive and negative
charges in an atom.
 Rutherford determined that the positive charges (protons) were
located in the center of the atom and the negative charges
(electrons) were scattered around the nucleus
 Bohr’s theory said that the protons are in the middle and the
electrons travel in specific energy levels and orbits around the
nucleus
 Modern model- protons and neutrons in the nucleus, electrons
on energy levels

17. REVIEW
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 An atom is made up of protons (+),
neutrons (no charge), and electrons(-).
 The protons and neutrons are found in the
nucleus
 There has to be an equal number of protons
and electrons because atoms have no net
charge!
 Atomic mass is the number of protons and
neutrons
 Atomic number is the number of protons
(which is the same as the number of electrons)

18. VOCABULARY
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Atom: the smallest particle of an element that has the chemical
properties of the element
Nucleus: found in the centre of the atom and contains the protons and
neutrons
Proton: a positively charged particle found in the nucleus of an atom
Neutrons: an uncharged particle found in the nucleus of an atom
Electron: negatively charged particles that move around outside the
nucleus of the atom
Isotopes: atoms of the same element that have a different number of
neutrons. Chlorine atoms have 17 protons, but some atoms of chlorine have 18
or 20 neutrons these atoms are the isotopes of chlorine

19. ATOMS FORM IONS
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 Ions: formed when an atom
loses or gains one or more
electrons(- or + charge)
 Cation: formed when an atom
loses an electron (+ charge)
 Anion: formed when an atom
gains an electron (-charge)

20. ELEMENTS ARE ORGANIZED BY
SIMILARITY
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 Modern Periodic
Table organized by the
atomic # of the
elements
 Dmitri Mendeleev
began organizing
elements by their
physical and chemical
properties (1860’s)

21. Periodic table of the
elements
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Mendeleev produced
the first periodic table
Called the periodic
table because a
periodic, or repeating
pattern of properties
of the elements

22. PERIODIC TABLE
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 Period: each row of the periodic
table is called a period. If you
read from left to right one proton
and one electron are added from
one element to the next
 Group/Family: Each column of
the table is called a group or
family. Elements in a group share
similar properties.
Groups/Families are read from
top to bottom

23. ATOMIC SIZE ON THE PERIODIC
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 Left to right atomic size decreases
 Top-to-bottom atomic size increases

24. MORE PROPERTIES OF
PERIODIC TABLE
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25. PERIODIC TABLE HAS DISTINCT
REGIONS
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Reactive: indicates how likely an element is to undergo
a chemical change
Most elements are somewhat reactive and combine
with other materials
The most reactive are in groups (up/down) 1 and 17
The least reactive are in the group (up/down) 18

26. ELEMENTS COMBINE BY THE
OUTSIDE ELECTRONS
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 All of the electrons in the combining elements do not interact with
each other to form compounds….
 Valence Electrons: Only the electrons in the element’s outside
energy level interact with each other.
 The most stable configuration has 8 electrons in the outer energy
level.
 Elements in group 1 have 1 electron in the outside energy level and
elements in group 17 have 7 electrons in the outside energy level so
they react with each other easily to form compounds and fulfil the
8 electrons stable configuration.

27. METALS
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 Most elements are metals
 Metals are elements that
conduct electricity and
heat, have a shiny
appearance, and can be
shaped by pounding
(malleability), bending,
or being drawn into a
thin wire (ductility)

28. METAL TYPES
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Reactive metals: Group (up/down) 1 most reactive
Transition Metals: Groups 3-12 (up/down) are
generally less reactive than most metals.

29. RARE EARTH METALS
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 Top row of the two rows of metals that are outside of the main periodic table
 Also known as Lanthanides because they follow the element lanthanum (La)
on the table
 Scientists once thought these metals were available only in tiny amounts on
the Earth

30. ACTINIDE
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• bottom row of the
two rows of metals
that are outside of
the main periodic
table
• The Actinide series
is all radioactive
and some are not
found in nature.

31. NONMETALS
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 Nonmetals: the elements on the right side of the periodic table
 Many are gases at room temperature, dull surfaces on the solid nonmetals,
cannot be shaped by ductility or malleability

32. HALOGENS
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 Elements in group 17
 7 valence electrons
 Greek “forming salts
 Very reactive non-
metals that easily form
compounds with
metals. These
compounds are known
as salts.

33. NOBLE GASES
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 Group 18 on the
periodic table
 8 valence electrons
 Noble or inert
because they
almost never react
with other elements

34. METALLOIDS
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 Have properties of both metals and nonmetals
 Located on either side of the zigzag line separating metals and nonmetals
 Most common in Silicon

35. RADIOACTIVITY
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 Radioactivity: the process by
which the nucleus of an atom
releases energy and particles
 Marie Curie was the first person
to isolate two radioactive elements
(polonium and radium)
 An isotope is radioactive if the
nucleus has too many or too few
neutrons

36. RADIOACTIVE DECAY
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 Radioactive atoms produce
energy and particles from their
nuclei
 The identity of these atoms
changes because the # of protons
changes. (radioactive decay)
 Occurs at a steady rate
characteristic to each isotope
 The amount of time for one-half
of the atoms to decay is called the
half-life of the isotope

37. RADIOACTIVE DECAY
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 Parent decays into a daughter isotope.
 Combination of both is 100%
 Parent starts at 100% and decays to 50%
 100% 1 half-life to 50% (daughter 50%)
 50% 2 half-lives to 25% (daughter 75%)
 25% 3 half-lives to 12.5% (daughter 87.5%)
 12.5% 4 half-lives to 6.25% (daughter 93.75%)

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