Download Atomic Structure - Pleasantville High School

ATOMIC
STRUCTURE
DO NOW

What is a proton, a neutron, and an electron?
What is the charge of each?
 Where are they found in the atom?

• A proton, neutron, and an electron are all sub-atomic
particles found in atoms.
• A proton has a positive charge.
• A neutron has a neutral charge, or no charge.
• An electron has a negative charge.
• Protons and neutrons are found in the nucleus of the
atom.
• Electrons are found in orbitals around the atom.
THE ATOM
All matter is composed of tiny particles called
Atoms.
 All atoms are composed of smaller particles:
 Protons- atomic particles with a positive
charge.


Neutrons- atomic particles with no charge.

Electrons- atomic particles with a negative
charge
ATOMIC NUMBER

The atomic number- depends on the number of
protons in a type of element.
 In an electrically neutral atom, the number or
electrons is the same at the number of protons.
 Number of protons = number of electrons
Atomic Number
Atomic Mass
ATOMIC MASS

Atomic mass is based on the number of protons and
neutrons in an atom of an element.
A certain element has an atomic mass of 16 and an
atomic number of 8. The atomic number equals the
number of protons in the element’s atoms. To find the
number of protons, subtract the atomic number (8) from
the atomic mass (16).
16
- 8
8 neutrons
DALTON’S THEORY
 All
matter is made of atoms. Atoms are
indivisible and indestructible.
 All atoms of a given element are identical
in mass and properties
 Compounds are formed by a combination
of two or more different kinds of atoms.
 A chemical reaction is a rearrangement
of atoms.
J.J. THOMPSON’S THEORY
Discovered a negatively charged particle in the
atom, that he named the electron.
 Chocolate Chip Cook Model of the Atom.
 Positive and negative charges are distributed
evenly throughout the atom.

LORD RUTHERFORD’S
THEORY

Gold Foil Experiment:
Fired alpha particles at a piece of gold foil.
 Most particles when through the foil, but about 1 in
10,000 got deflected.

The new evidence allowed him to formulate a
new atomic model with a central nucleus.
 He suggested that the dense positive charge was
in the center and the negatively charged
electrons were being held in place by attractive
forces.


Remember, opposites attract!
NIELS BOHR’S THEORY
 Bohr
refined Rutherford’s model and
suggested that the electrons were in
orbitals.
 This is called the “Planetary Model.”
WHAT WE KNOW TODAY
 Electrons
are arranged in energy levels
or orbitals around the nucleus of an
atom.

First shell = maximum of two electrons.
 Second shell = maximum of eight
electrons.
 Third shell = maximum of eight
electrons.

 So
how do we know how many electrons
are in an atom of a certain element?
The number of protons are equal to
the number electron. There is an
exception….Ions
EARLY GREEK THEORIES
 400
B.C. - Democritus thought matter
could not be divided indefinitely.
• This led to the idea of atoms in a void.
fire
Democritus
earth
air
water
• 350 B.C - Aristotle modified an earlier
theory that matter was made of four
“elements”: earth, fire, water, air.
Aristotle
• Aristotle was wrong. However, his
theory persisted for 2000 years.
JOHN DALTON

1800 -Dalton proposed a modern atomic model
based on experimentation not on pure reason.
• All matter is made of atoms.
• Atoms of an element are identical.
• Each element has different atoms.
• Atoms of different elements combine in
constant ratios to form compounds.
• Atoms are rearranged in reactions.
• His ideas account for the Law of Conservation of
Mass
THE LAW OF CONSERVATION OF MASS
Atoms are neither created nor
destroyed
The Law of Constant Proportions
Atoms in compounds are in fixed
ratios…CO2 is a different ration
than CO.
ERNEST RUTHERFORD (MOVIE: 10 MIN.)

Rutherford shot alpha () particles at gold foil.
Zinc sulfide screen
Thin gold foil
Lead block
Radioactive
substance path of invisible
-particles
Most particles passed through.
So, atoms are mostly empty.
Some positive -particles
deflected or bounced back!
Thus, a “nucleus” is positive &
holds most of an atom’s mass.
BOHR’S MODEL
• Electrons orbit the nucleus in “shells”
• Electrons can be bumped up to a higher shell
if hit by an electron or a photon of light.
There are 2 types of spectra: continuous spectra &
line spectra. It’s when electrons fall back down that
they release a photon. These jumps down from “shell”
to “shell” account for the line spectra seen in gas
discharge tubes (through spectroscopes).
BOHR - RUTHERFORD DIAGRAMS
Putting all this together
 To draw them you must know the # of protons, neutrons, and
electrons (2,8,8,2 filling order)
 Draw protons
 Draw electrons around in shells

He
p+
2
2 n0
Li
3 p+
4 n0
Li
shorthand
3 p+ 2e– 1e–
4 n0
Be
B
4
p+
5 n°
O
Al
5
p+
6 n°
13 p+
14 n°
Na
8
2e– 6e–
p+
8 n°
11
2e– 8e– 1e–
p+
12 n°
ISOTOPES
One of two or more kinds of atoms of the same
element that differ from each other in their
atomic masses.
 There are elements whose atoms differ in the
number of neutrons.
 For example there are two kinds of atoms in
Neon.

Some have 10 neutrons and others have 12 neutrons.
 Neon with 10 neutrons has a lower atomic mass than
Neon with 12 neutrons…THEY ARE BOTH NEON!

CARBON ISOTOPES
C-12, C-13, and C-14 are all isotopes of the
element Carbon.
 The number 12, 13, and 14 all refer to the atomic
mass of atoms.
 There are still 6 protons in each, however the
number of neutrons change.


12
6C
13
6 C
14
6
C
HOW IS THE ATOMIC MASS DETERMINED?

Naturally occurring europium (Eu) consists of
two isotopes with a mass of 151 and 153. Eu -151
has an abundance of 48.03% and Eu-153 has an
abundance of 51.97%. What is the atomic mass of
europium?