Matter Is Made
Up Of Atoms
Chapter 4
Structure of the Atom


An atom is the smallest particles of
matter that retain the matter’s properties.
Atoms have TWO PARTS:
• A NUCLEUS
• An ELECTRON CLOUD
A Model of the Atom
The Nucleus of the Atom



The NUCLEUS of the atom is the
SMALL, DENSE, SOLID central region
of the atom.
The NUCLEUS is made up of TWO
smaller particles [sub-atomic particles]
called:
PROTONS and NEUTRONS
PROTONS

PROTONS are small sub-atomic
particles that have a POSITIVE
ELECTRICAL CHARGE.
P+
 Protons are responsible for the
identity of an element.

Represented by the symbol
The ATOMIC NUMBER



The number of PROTONS in an atom’s
nucleus is called the ATOMIC NUMBER
of the atom.
Atoms can have from 1 to 109 protons,
depending on which element is being
referenced.
The number of PROTONS determines
which element an atom belongs to.
NEUTRONS

NEUTRONS are the other subatomic
particle found in the atom’s nucleus.

NEUTRONS are NEUTRAL; they have
NO ELECTRICAL CHARGE.

The symbol for a NEUTRON is:
o
N
The ATOMIC MASS NUMBER

The ATOMIC MASS NUMBER is the
COMBINED NUMBER of PROTONS
and NEUTRONS in the atom’s nucleus.

Together, the protons and neutrons are
responsible for 99.999% of the atom’s
total mass.

Look at a Periodic Table.

Now look at the ATOMIC MASS
NUMBERS for the elements.
What do you notice about these
numbers?

 THEY
CONTAIN DECIMALS
How atomic mass numbers get
their decimals.

We learned earlier that the AMN is the
total of an atoms protons and neutrons
combined.

How can this give a number with a
decimal?

While ALL atoms of an element have the
SAME NUMBER of PROTONS they
don’t all have the same number of
NEUTRONS….

The number of NEUTRONS can vary
between atoms of the same element.
ISOTOPES

Atoms of an element that vary in AMN’s
due to differing numbers of NEUTRONS
are called ISOTOPES.

The ATOMIC MASS NUMBER reported
for an element on the PERIODIC TABLE
is an AVERAGE of all the different
ISOTOPES of that element.
Writing Isotopes

Isotopes can be written two ways:

1. Chemical Symbol and AMN
-more simple


Example C-14

2. Chemical Symbol with AN and AMN
-More detailed


Example
14 C
6
The Electron Cloud

Unlike the NUCLEUS, the ELECTRON
CLOUD:

Is very large [about 10,000x the size of
the nucleus].
Is NOT solid; it is an area of EMPTY
SPACE surrounding the nucleus.
Contains only one subatomic particle.


The ELECTRON


The ELECTRON is the smallest of the subatomic particles.
It takes 1834 electrons to have about the same
mass as ONE proton!
e-

The symbol for an electron is:

Neutral atoms have as many electrons
as they do protons!
• The ATOMIC NUMBER
is also the number
of electrons in the Electron Cloud.
Divisions of the Electron Cloud



The Electron Cloud is divided into 7 main
regions called PRINCIPLE ENERGY
LEVELS.
The PEL’s move outward away from the
nucleus…1 is closest….7 is farthest
away!
Each PEL can hold a certain number of
electrons.







PEL 1 = 2 ePEL 2 = 8 ePEL 3 = 18 ePEL 4 = 32 ePEL 5 = 32 ePEL 6 = 32 ePEL 7 = 32 e-
Sublevels

Each PEL can further be divided into
smaller divisions called SUBLEVELS.

The number of sublevels in a PEL
depends on it’s distance from the
nucleus.






PEL 1 has only 1 sublevel, called S
PEL 2 has two sublevels: S and P
PEL 3 has three sublevels: S, P and D
PEL 4-7 has four sublevels: S, P, D and F
S sublevels are spherical and hold a max
of 2 e-.
P sublevels are figure 8-like and hold a
max of 6e-.

D sublevels are “mushroom” shaped
and lie along the X, Y, Z plane.

D sublevels hold a max of 10 e-.

F sublevels assume different shapes
along the X, Y, Z plane and hold a max
of 14 e-.
Sublevel Filling Patterns

Because the energy required to maintain
the orbit of the more complex sublevels
is more than that of more simple orbits, a
sublevel will not completely fill before the
next higher one begins receiving
electron.
AUFBAU Electron Distribution Chart







1s
2s
3s
4s
5s
6s
7s
2p(10)
3p(18)3d
4p(36)4d
5p(54)5d
6p(86) 6d
7p 7d
[Ne =10]
[Ar=18]
4f
5f
6f
7f
[Kr=36]
[Xe=54]
[Rn=86]
Orbital Notation

Orbital Notation is used to illustrated the
distribution of e- within the e- cloud.
Number of e- in sublevels



Example
Mg – 1s2 2s2 2p6 3s2
Symbol
Sublevels
Practice Problems




Write out the electron configuration of:
1. Oxygen
2. Calcium
3. Iodine
Shorthand e- Configurations




Locate the NOBLE GAS immediately
before the element.
Write the noble gas’ symbol in a bracket
example [ Xe ]
Subtract the AN of the noble gas from
the element, then distribute the
remaining electrons beginning at the
next sublevel.
Practice

Write the shorthand configuration for
Barium.
nearest noble gas is Xe
with 54 e-. Xe fills the
sublevels through 5p.
56 – 54 = 2 e- to distribute beginning at 6s.

Ba = 56 e-

Ba [ Xe ] 6s2

Practice
Write shorthand configurations for:

• A. Arsenic
• B. Iodine
The most important PEL is the outermost
one of the atom.
The electrons on this level are involved
in forming chemical bonds with other
atoms. The electrons in the outermost
PEL are known as
VALENCE ELECTRONS,
or Ve- for short.