Download Chapter 4- Atomic Structure

CHAPTER 4
Atomic Structure
Atoms
• Atoms– the smallest particle of an
element. Named by Democritus, a Greek
philosopher.
What are atoms?
Atoms are the basic building blocks
of matter that make up everyday
objects. A desk, the air, even you are
made up of atoms!
There are 90 naturally occurring
kinds of atoms. Scientists in labs
have been able to make about 25
more.
Dalton’s Atomic Theory
1. All elements are composed of atoms.
Atoms can not be broken into smaller
pieces. They are extremely small.
2. In any element, all the atoms are the
same.
3. Atoms of 2 or more elements can
combine to form compounds.
Compounds contain atoms of more
than one element.
Dalton’s Atomic Theory cont.
4. In a particular compound, atoms of
different elements always combine in the
same way. The ratio of their masses is
always the same for that compound.
EX: H 2O H-O 2:1 same ratio in all
samples of water.
Dalton’s Atom
Dalton’s Model of an atom showed an
atom as a solid sphere without
subatomic particles
Thomson’s model of the Atom
Thomson, used an electric current to learn more
about atoms. Thomson’s experiments provided the
first evidence that atoms are made of even smaller
particles, subatomic particles.
In Thomson’s model of the atom, the negative charges
were evenly scattered throughout an atom filled with a
positively charged mass of matter.
Rutherford’s Atomic Theory
•
Through his testing using a Gold Foil Experiment Rutherford
concluded that the positive charge of an atom is not evenly
spread throughout the atom. The positive charge is
concentrated in a very small, central area that Rutherford called
the nucleus.
•
The nucleus is a dense, positively charged mass located in the
center of the atom.
•
According to Rutherford’s model, all of an atom’s positive
charge is concentrated in its nucleus.
Sec 4.2
The Subatomic Particles of an Atom
Protons- Positively charged subatomic particle that is found in the
nucleus of an atom.
Electrons- Negatively charged subatomic particle that is found in the
space outside the nucleus.
Neutrons- A neutral subatomic particle that is found in the nucleus of an
atom. It has a mass almost exactly equal to that of a proton.
Each positive charge in an atom is balanced by a negative
charge because atoms are neutral. (# of electrons = # of protons)
Protons, electron, and neutrons can be distinguished by
mass, charge, and location in an atom. (this is how we can tell them
apart)
The protons and the neutron have almost the same mass. An electron has
far less mass than either a proton or a neutron. About 2000 electrons equal
the mass of one proton.
ATOMIC NUMBER– the number of
protons in the nucleus of the atoms in
an element. Atoms of different elements
have different number of protons.
ATOMIC MASS NUMBER–The atomic
mass of an atom is the sum of the
protons and neutrons in the nucleus
of that atom. Electrons have a much
smaller mass than protons and
neutrons therefore most of the atom’s
mass is in the nucleus.
# of neutrons + # of protons (atomic number ) = atomic mass number
Isotopes of an element have the same
atomic number ( same # of protons) but
different mass numbers because they
have different numbers of neutrons.
Example:
C-12
C- 14
14 total mass
Carbon 12
Total mass
Atomic #
(6 protons in
nucleus)
12
6
C
!
12 total mass
Carbon 14
________________
atomic
mass
-6 protons
---------6 neutrons
-6 protons
14
6
6 protons
C
8 neutrons
in nucleus
hyperlink to Isotopes
http://www.colorado.edu/physics/2000/isotopes/index.html
Hydrogen
Hydrogen-1
Deuterium
Hydrogen-2
Tritium
Hydrogen-3
The most common isotope of hydrogen has no neutrons at all. There is
also a hydrogen isotope called deuterium with one neutron and tritium,
with two neutrons.
Sec 3
Bohr’s Model of the Atom
• Scientist, Bohr focused on the electrons of an atom.
• Bohr believed that electrons moved with constant
speed in fixed orbits around the nucleus, like planets
around the sun.
• If an atom gains or loses energy, the energy of an electron
can change. The possible energies that electrons in an
atom can have are called energy levels.
• An electron in an atom can move from one energy level to
another when the atom gains or loses energy. (when an
electron moves to a higher energy level the electron has gained
energy)
Bohr’s Model of an Atom
The region of space
around the nucleus
where an electron is
likely to be found is
called an Electron
Orbital.
Bohr’s Model of an
atom shows subatomic
particles where the
electrons are in fixed
circular orbitals about
the nucleus.
Evidence of Energy Levels
The movement of electrons between energy levels explain the light you
see when fireworks explode. Light is a form of energy. Heat from the
explosion causes some electrons to move to higher energy levels.
When they move back to lower energy levels they give off energy as
light. Because no 2 elements have the same set of energy levels,
different elements emit different colors of light.
An electron configuration is the arrangement of electrons in the orbitals of an
atom. The most stable electron configuration is the one in which the electrons are
in orbitals with the lowest possible energies.
When all the electrons in an atom have the lowest possible
energies, the atom in said to be in its ground state.
If an atom gains enough energy, one of its electrons can
move to an orbital with a higher energy level. This
configuration is referred to as an excited state. At an excited
state the atom is less stable than at ground state. Eventually
the electron loses energy and the atom returns to the ground
state.
Electron Cloud Model
• Today, we know that electrons move in a less
predictable way.
• An electron cloud is a visual model of the most
likely locations for electrons in an atom.
• Scientists use the electron cloud model to
describe the possible locations of electrons
around the nucleus.
• The electron cloud represents all the orbitals in
an atom.
Electron Cloud Model
In the Electron
Cloud Model the
moving electrons
are represented by
a cloud.
• The level in which an
electron has the least
energy is the lowest
energy level, next to the
nucleus. It has only one
orbital in it. Higher
energy levels have more
than one orbital.
• Each orbital can only
contain 2 electrons.
• Therefore the maximum
number of electrons in an
energy level is twice the
number of orbitals.
Energy
Level
Number of
Orbitals
Maximum
Number of
Electrons
1
1
2
2
4
8
3
9
18
4
16
32
Electrons fill low energy orbitals
(closer to the nucleus) before they
fill higher energy ones.
ATOMIC ORBITALS
Each orbital has a name
s orbital
p orbitals
d
orbitals
One of the 7
f orbitals
sublevel
orbital
maximum # of electrons
s
1
2
p
3
6
d
5
10
f
7
14
An electron configuration is the arrangement of
electrons in the orbitals of an atom.
To show the electron orbitals you can write it as:
Examples of Electron Configurations
Element
# of Electrons in Element
Electron Configuration
He
2
1s
Li
3
1s
Be
4
1s
O
8
Cl
17
1s
1s
Democritus
Aristotle
(said matter is made
up of tiny particles
called ATOMS that
cannot be divided)
(said matter made up of earth
air, fire, water)
+ - -+
+
+
+
Thomson
Dalton
(solid sphere, no
subatomic particles, had
a predictable mass for a
given element)
--
(discovered negative
charges-thought they were
scatter throughout atom)
+ -
Bohr’s Model -electrons in fixed orbitals like plants around sun
Rutherford
(said positive charge
was concentrated in
the center of atom—
called it the nucleus
Electron Cloud Model- used
today. Electron location by
probability—where it is most likely to
be located
+
-
+
-
+
+ +
+
-
• Dalton Model
• Thomson Model
• Electron Cloud Model
• Bohr Model
• Rutherford Model