The document outlines the fundamental principles of atomic structure and the periodic table, introducing Dalton's atomic theory which posits that all matter is composed of indivisible atoms. It describes the composition of atoms, including protons, neutrons, and electrons, and explains concepts such as nuclides, isotopes, and the organization of elements in the periodic table. Furthermore, it discusses electronic configurations, periodic properties, and trends such as atomic size and ionization energy.

1. 1

2. CHAPTER 2:
ATOMIC STRUCTURE AND THE
PERIODIC TABLE

3. Atomic Theory of Matter
• Dalton's atomic theory was the first complete
attempt to describe all matter in terms of atoms
and their properties.

4. Postulates of Dalton’s Atomic Theory
i.All matter is composed of indivisible atoms. An atom is an
extremely small particle of matter that retains its identity during
chemical reactions.
ii.An element is a type of matter composed of only one kind of
atom.
iii.A compound is a type of matter composed of atoms of two
or more elements chemically combined in fixed proportions.
iv.A chemical reaction involves the rearrangement of the
atoms present in the reacting substances to give new chemical
combinations present in the substances formed by the reaction.

5. Structure of the Atom
•The atom is composed of two kinds of particles:
Nucleus
Central core
Contains protons and neutrons
Positively charged
Contains most of the atom’s mass
Electrons
Very light
Negatively charged
Exist in the region around the nucleus

6. Proton
A nuclear particle having a positive charge, equal to
that of the electron, and a mass more than 1800 times
that of the electron.
•The number of protons in an atom is called the
atomic number, Z.
•An element is a substance whose atoms have the
same number of protons & thus the same atomic
number, Z.

7. Nuclide
•An atom characterized by a certain atomic number, Z,
and mass number, A.
•Nuclide symbol
•Examples: 7
Li
3
13
C
6
23
Na
11

8. •Write the nuclide symbol for the atom that has
19 protons and 20 neutrons.
39
K
19
Atomic number: Z = 19
The element is potassium, K.
Mass number: A = 19 + 20 = 39
The nuclide symbol is

10. Isotopes have
the same atomic
number (p+), but
different mass
numbers (p++ no)

11. NB: If two or more isotopes of an element are present in
proportional amounts, then the atomic weight is the
average of all the isotopes.

12. EXERCISE
An element has four naturally occurring isotopes. The
mass and percentage of each isotope are as follows:
Percentage Abundance Mass (amu)
1.48 203.973
23.6 205.9745
22.6 206.9759
52.3 207.9766
What is the atomic weight & name of the element?

13. DID YOU KNOW?
• 700 different versions of the periodic “table”
have been published in the past 100 years?

14. Theodor Benfey’s spira table (1964)
James Franklin
Hyde‘s curled ribbon
table in 1975.
Marco Piazzalunga's Circular
Periodic Table, 2011

15. Periodic Table of the Elements
•A tabular arrangement of elements in rows and
columns, highlighting the regular repetition of
properties of the elements.

16. •A period consists of the elements in one horizontal row.
•A group consists of the elements in one
vertical column.
•Groups are numbered using two systems: IUPAC
Numbers 1 through 18
Older system Roman numerals I–VIII and
the letters A andB

18. Metal
•A substance or mixture that has a characteristic luster
or shine and is generally a good conductor of heat and
electricity.
Nonmetal
not exhibit the characteristics of
•An element that does
Metalloid
•An element having characteristics of both metals
and nonmetals
a metal.

19. General, Organic, and Biological Chemistry, H.S. Stoker, 4th Ed., 2007

20. THE ELECTRONIC STRUCTURE
• e-s restricted to specific regions within the extranuclear
portion of the atom, determined by the amount of energy
the electrons possess.
• Space in which e-s move rapidly about a nucleus is
divided into subspaces called shells, subshells & orbitals.
 Shell: a region of space around a nucleus that contains e-s
having approximately the same energy. Typically numbered
1,2,3…
 Subshell: a region of space within an electron shell that
contains electrons that have the same energy. Designated s,
p, d, f
 Orbital: is a region of space within an electron subshell where
an electron with a specific energy is most likely to be found.

21. General, Organic, and Biological Chemistry, H.S. Stoker, 4th Ed., 2007

22. NB: An electron orbital, independent of all other considerations, can
accommodate a maximum of 2 electrons.

23. e- configurations & orbital diagrams
 Electron subshells are filled in order of
increasing energy.
 Electrons occupy the orbitals of a subshell such
that each orbital acquires one electron before
any orbital acquires a second electron.
 No more than two electrons may exist in a given
orbital and MUST have opposite spins.
Hund’s Rule: e-s occupy a degenerate set of orbitals singly
before a second opposite spin accompanies it.

24. e- configurations & orbital diagrams
Order of filling subshells with e-s

25. Electron Configuration & Periodic Table

26. Orbital Diagrams
• Each box represents one orbital.
• Half-arrows represent the electrons.
• The direction of the arrow represents the spin of the electron.
O

27. 1s
2s
2p
3s
3p
3d
4s
Electronic configuration : 1s2
27
Nitrogen
2s22p3
Fe
Mn
V
Ti
Sc
K
Na
Zn
Cu
Ni
Cr Co
Mg
Ca
Be
H
As
O
S
Se
F
Cl
Br
Ga
C
Si
Ge
N
P
He
Ne
Ar
Kr
1 2 GROUP 3 4 5 6 7 0
Li
Al
B
1
2
3
4
Hund’s Rule

28. 28
Neon
1s
2s
2p
3s
3p
3d
4s
1s2
Electronic configuration: 2s22p6
Fe
Mn
V
Ti
Sc
K
Na
Zn
Cu
Ni
Cr Co
Mg
Ca
Be
H
As
O
S
Se
F
Cl
Br
Ga
C
Si
Ge
N
P
He
Ne
Ar
Kr
1 2 GROUP 3 4 5 6 7 0
Li
Al
B
1
2
3
4
Hund’s Rule

29. Exercise
1. 1s2
2s2
2p6
3s2
3p6
4s2
3d6
29
2. [Ar] 4s0
3d6
Identify elements which posses the following
electron configurations:
3. [Ne] 3s2
3p6

30. Periodic Properties
• Chemical properties repeat themselves in a regular
manner among the elements because e- configurations
repeat themselves in a regular manner among the
elements.

31. Atoms Sizes/Radii & Ions
Anions larger than parent
atoms
Cations smaller than parent
atoms

32. Trends: Atomic & Ionic Sizes
•Atomic size increases down a group
•Atomic size decreases from L to R across a period.

33. Ionization energy (IE)
The energy required to remove an e- from an
isolated, gaseous atom or ion in its ground state:
X(g) → X+(g) + e- IE1
X+(g) → X2+(g) + e- IE2, etc.
Trend: IE increases from L to R across a period, &
decreases down a group.

35. Electron Affinity (EA)
The potential energy change associated with
the addition of an e- to a gaseous atom or ion
in its ground state.
X(g) + e- → X-(g) EA1 < 0
X-(g) + e- → X2-(g) EA2 > 0
Trend: EA becomes more exothermic from L to
R across a period & from bottom to top in a
group.