This document provides information about atomic structure. It discusses the basic parts of an atom including protons, neutrons, and electrons. Early atomic models proposed by Rutherford and Bohr are described, noting their limitations in explaining experimental observations. The modern quantum mechanical model represents electrons using quantum numbers and wave functions or "fuzzy clouds" to describe atomic orbitals. Electrons occupy different energy levels and sublevels based on their quantum numbers.

1. CHEMISTRY
PROJECT
BY
COMPUTERCAREERS

2. ATOMIC STRUCTURE

3. What is an Atom?
• Matter is anything that takes up space and has
mass.
• All matter is made of atoms
• Atoms are the building blocks of matter, sort of
how bricks are the building blocks of houses.

4. Parts of Atom
• An atom has three parts:
• Proton = positive
• Neutron = no charge
• Electron = negative
• The proton & neutron are
found in the center of the
atom, a place called the
nucleus.
• The electrons orbit the
nucleus.

5. ATOMIC STRUCTUREATOMIC STRUCTURE
Electrons are arranged in Energy Levels or
Shells around the nucleus of an atom.
• first shell a maximum of 2 electrons
• second shell a maximum of 8 electrons
• third shell a maximum of 8 electrons

6. ATOMIC STRUCTUREATOMIC STRUCTURE
There are two ways to represent the atomic
structure of n element or compound;
1. Electronic Configuration
2. Dot & Cross Diagrams

7. ELECTRONIC CONFIGURATIONELECTRONIC CONFIGURATION
With electronic configuration elements are
represented numerically by the number of
electrons in their shells and number of shells. For
example;
N
Nitrogen
14
2 in 1st
shell
5 in 2nd
shell
configuration = 2 , 5
2 + 5 = 7 7

8. DOT & CROSS DIAGRAMSDOT & CROSS DIAGRAMS
With Dot & Cross diagrams elements and
compounds are represented by Dots or Crosses
to show electrons, and circles to show the
shells. For example;
Nitrogen N XX X
X
XX
X
N
7
14

9. 1910
Ernest Rutherford
oversaw Geiger and Marsden carrying out
his famous experiment.
they fired Helium nuclei at a piece of gold
foil which was only a few atoms thick.
they found that although most of them
passed through. About 1 in 10,000 hit

10. Rutherford’s InventionRutherford’s Invention
gold foil
helium nuclei
They found that while most of the helium nuclei passed
through the foil, a small number were deflected and, to
their surprise, some helium nuclei bounced straight back.
helium nuclei

11. Rutherford’s new evidence allowed him to
propose a more detailed model with a central
nucleus.
He suggested that the positive charge was all in
a central nucleus. With this holding the
electrons in place by electrical attraction
However, this was not the end of the story.

12. ARISEN OF NEILS BOHRARISEN OF NEILS BOHR
1913
Niels Bohr
studied under Rutherford at the Victoria
University in Manchester.
Bohr refined Rutherford's idea by adding
that the electrons were in orbits. Rather
like planets orbiting the sun. With each
orbit only able to contain a set number of
electrons.

13. Rutherford’s alpha scattering experiment
source of
alpha
particles
Thin gold
foil
Photographic
film
Beam of α
particles
most pass
straight
through
1 in 20 000
deflected

14. Rutherford’s explanation
atoms of gold
in gold foil
Path of an α particle
nucleus of
gold atom
All these α particles pass
straight through the empty
space that makes up most of
the atom.
This α particle
passes close
enough to
nucleus to be
repelled
As α particles are positively charged,
the nucleus must contain positively
charged protons.

15. atoms of gold
in gold foil
nucleus of
gold atom
As only 1 in every 20 000
α particles are repelled the
nucleus must be very small.
Size of the nucleus

16. Rutherford’s model of the atom
Tiny nucleus
containing the
positively
charged
protons.
Rest of atom is
mostly empty space.
The negatively
charged
electrons are spinning
round the nucleus.

17. Section 3.1
The Limitations of Rutherford’s
Atomic Model
Chapter 3: Atomic Models and Properties of Atoms
• radiation must be emitted, so it
was expected that a continuous
spectrum of light energy was
being given off
• because of radiation, the electron
would lose energy and its orbit
would decrease until it spiraled
into the nucleus, destroying the
atom

18. Bohr Model of Atom
• The Bohr Model shows
all of the particles in the
atom.
• In the center is circles.
Each circle represents a
single neutron or proton.
Protons should have a
plus or P written on
them. Neutrons should
be blank or have an N.
• In a circle around the
nucleus are the
electrons. Electrons
should have a minus
sign or an e.
++
++
--
--

19. Bohr’s Atom
electrons in orbits
nucleus

20. Bohr's Model of the Atom
Bohr's model:
-electrons orbit the nucleus like
planets orbit the sun
-each orbit can hold a specific
maximum number of electrons
-electrons fill orbits closest to
the nucleus first.

21. Bohr's Model of the Atom
Niels Bohr (1913):
-studied the light produced when atoms
were excited by heat or electricity
Rutherford's model couldn't explain
why unique colours were obtained by
atoms of different elements
Bohr proposed that electrons are in
orbits & when excited jump to a higher
orbit. When they fall back to the
original they give off light

22. Bohr's Model of the Atom
e.g. fluorine:
#P =
#e-
=
#N =
9
9
10
9P
10N

24. Today’s quantum mechanical model of the atom
incorporates the wave properties of electrons.
Section 3.2
The Quantum Mechanical Model of
the Atom
An electron
density
diagram
represents an
atomic orbital.
Chapter 3: Atomic Models and Properties of Atoms
Wave functions, initially described by Erwin
Schrodinger, represent a region in space around a
nucleus where an electron will be found. This region of
space is called an atomic orbital

25. Section 3.2
The Quantum Mechanical Model of the Atom
The circle
does not
represent a
real boundary.
Chapter 3: Atomic Models and Properties of Atoms
Atomic orbitals can be visualized as “fuzzy
clouds”
• The higher the density of the “cloud,” the higher
the probability of finding an electron at that
point.
• The cloud has no definite boundary.
• The region where an electron will spend 90
percent of its time is depicted by drawing a
circle.

26. Section 3.1
Quantum Numbers Describe
Orbitals
Chapter 3: Atomic Models and Properties of Atoms
Electrons in the quantum mechanical model of the
atom are described using quantum numbers.
Three quantum numbers describe the distribution
of electrons in the atom and a fourth describes the
behaviour of each electron.
Symbols for the four quantum numbers:
n l ml ms

27. Section 3.2
The Principle Quantum
Number, n
Chapter 3: Atomic Models and Properties of Atoms
• Is the first quantum number
• Describes the energy level, or shell, of an
orbital
• All orbitals with the same n value are in the
same shell
• The larger the n value, the larger the size of the
shell
• Values can range from n = 1 to n = ∞
n = 1 first shell
n = 2 second shell
n = 3 third shell
n = 4 fourth shell

28. Section 3.2
The Orbital-Shape Quantum Number, l
Chapter 3: Atomic Models and Properties of Atoms
• Is the second quantum number
• Describes the shape of an orbital
• Refers to energy sublevels, or subshells
• Values depend on the value of n. They are positive
integers from 0 to (n – 1)
• Each value is identified by a letter
l = 0 orbital s
l = 1 orbital p
l = 2 orbital d
l = 3 orbital f
An energy sublevel is identified by combining n with the orbital letter.
For example, n = 2, l = 1: 2p sublevel

29. Section 3.2
The Magnetic Quantum Number, ml
s, p, and d orbitals have
characteristic shapes.
Chapter 3: Atomic Models and Properties of Atoms
• Is the third quantum number
• Indicates the orientation of the orbital in space
• For a given l there are (2l +1) values for ml
• The total number of orbitals for an energy level
is n2

30. NucleusNucleus
11stst
shellshell
22ndnd
shellshell
33rdrd
shellshell