Atomic structure

S.MORRIS 2006
PENDAHULUAN
Definisi
• Atom adalah partikel terkecil dari suatu elemen.
• Setiap elemen memiliki struktur atom yang unik.
• Menurut model atom Bohr, atom terdiri dari inti atom
(nucleus) yang dikelilingi oleh elektron.
• Nucleus terdiri dari proton (positif) dan neutron
(netral).
• Elektron yang mengelilingi inti atom berupa negatif.
Nomor Atom
• Semua elemen diurutkan dalam tabel periodik sesuai
dengan nomor atomnya.
Contoh : Hidrogen memiliki nomor atom 1
Helium memiliki nomor atom 2
HISTORY OF THE ATOM
460 BC
Democritus develops the idea of atoms
he pounded up materials in his pestle and
mortar until he had reduced them to smaller
and smaller particles which he called
ATOMA
(greek for indivisible)
HISTORY OF THE ATOM
1808
John Dalton
suggested that all matter was made up of
tiny spheres that were able to bounce around
with perfect elasticity and called them
ATOMS
HISTORY OF THE ATOM
1898
Joseph John Thompson
found that atoms could sometimes eject a far
smaller negative particle which he called an
ELECTRON
HISTORY OF THE ATOM
1904
Thompson develops the idea that an atom was made up of
electrons scattered unevenly within an elastic sphere surrounded
by a soup of positive charge to balance the electron's charge
like plums surrounded by pudding.
PLUM PUDDING
MODEL
HISTORY OF THE ATOM
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
HISTORY OF THE ATOM
helium nuclei
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.
– Most of the positively
charged “bullets” passed
right through the gold
atoms in the sheet of
gold foil without changing
course at all.
– Some of the positively
charged “bullets,”
however, did bounce
away from the gold sheet
as if they had hit
something solid. He
knew that positive
charges repel positive
charges.
HISTORY OF THE ATOM
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.
HISTORY OF THE ATOM
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.
Bohr’s Atom
electrons in orbits
nucleus
HELIUM ATOM
Shell
proton
+
-
N
N
+
electron
What do these particles consist of?
-
neutron
ATOMIC STRUCTURE
Particle
Charge
Mass
proton
+ ve charge
1
neutron
No charge
1
electron
-ve charge
nil
ATOMIC STRUCTURE
He
2
4
Atomic number
the number of protons in an atom
Atomic mass
the number of protons and
neutrons in an atom
number of electrons = number of protons
ATOMIC 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
ATOMIC STRUCTURE
There are two ways to represent the atomic
structure of an element or compound;
1.
2.
Electronic Configuration
Dot & Cross Diagrams
ELECTRONIC CONFIGURATION
With electronic configuration elements are represented
numerically by the number of electrons in their shells
and number of shells. For example;
Nitrogen
2 in 1st shell
5 in
2nd
shell
configuration = 2 , 5
2
+
5 = 7
N
7
14
ELECTRONIC CONFIGURATION
Write the electronic configuration for the following
elements;
a)
Ca
20
b)
Na
40
2,8,8,2
d)
Cl
17
35
2,8,7
11
23
c)
2,8,1
e)
Si
14
28
2,8,4
O
8
16
2,6
f)
B
5
11
2,3
DOT & 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;
X
Nitrogen
X X
N
XX
X X
N
7
14
DOT & CROSS DIAGRAMS
Draw the Dot & Cross diagrams for the following
elements;
X
8
17
X
a) O
b)
Cl 35 X
16
X
X
X
X
X
X
X X X Cl X X
X
X
X
O
X
X
X
X
X
X
X
X
X
Wave Model
The Wave Model
• Today’s atomic
model is based on
the principles of
wave mechanics.
• According to the
theory of wave
mechanics,
electrons do not
move about an
atom in a definite
path, like the
planets around the
sun.
The Wave Model
• In fact, it is impossible to determine the exact
location of an electron. The probable location of
an electron is based on how much energy the
electron has.
• According to the modern atomic model, at atom
has a small positively charged nucleus
surrounded by a large region in which there are
enough electrons to make an atom neutral.
Electron Cloud:
• A space in which
electrons are likely to be
found.
• Electrons whirl about the
nucleus billions of times
in one second
• They are not moving
around in random
patterns.
• Location of electrons
depends upon how much
energy the electron has.
Electron Cloud:
• Depending on their energy they are locked into a
certain area in the cloud.
• Electrons with the lowest energy are found in
the energy level closest to the nucleus
• Electrons with the highest energy are found
in the outermost energy levels, farther from
the nucleus.
Indivisible Electron
Greek
X
Dalton
X
Nucleus
Thomson
X
Rutherford
X
X
Bohr
X
X
Wave
X
X
Orbit
Electron
Cloud
X
X
PARTIKEL BERMUATAN
• Muatan negatif elektron yaitu 1.6 x 10-19 Coulomb
• Massa elektron yaitu 9.11 x 10-31 kg
• Muatan ion positif : suatu kelipatan dari muatan
elektron dengan tanda muatan yang berlawanan.
• Partikel yang diionisasikan tunggal, besar
muatannya sama dengan muatan elektron.
• Partikel yang diionisasikan rangkap, muatan ion
menjadi dua kali muatan elektron.
• Massa suatu atom sama dengan berat atom
dikalikan dengan 1.66 x 10-27 kg.
• Jari – jari elektron kira-kira 10-15 m , jari – jari atom
10-10 m
SIFAT DASAR ELEKTRON
• Elektron bergerak mengelilingi inti atom.
• Elektron bermuatan negatif.
• Elektron bergerak dengan arah yang sama
dan menghasilkan arus listrik.
• Elektron direpresentasikan dengan e-.
• Elektron yang letaknya jauh dari nucleus
memiliki energi yang lebih besar
dibandingkan elektron yang berada dekat
dengan nucleus.
SUMMARY
1. The Atomic Number of an atom = number of
protons in the nucleus.
2. The Atomic Mass of an atom = number of
Protons + Neutrons in the nucleus.
3.
The number of Protons = Number of Electrons.
4.
Electrons orbit the nucleus in shells.
5.
Each shell can only carry a set number of electrons.