Transcript Atomic Models

The Structure of Matter
Atomic Models
Subatomic Particles
Forces Within the Atom
Part One: Atomic models past and
present
Atomic Models Throughout History






Greek (~400 BC)
Dalton (1800)
Thomson (1897)
Rutherford (1908)
Bohr (1913)
Wave Model
Greek (~400 BC)



Atomos: indivisible
Democritus said the smallest piece of
matter was an atom
Theory wasn’t accepted for 2100 years
Dalton (1800)




All elements are composed of atoms.
Atoms are indivisible and indestructible
Atoms of the same element are exactly
alike
Atoms of different elements are different
Compounds are formed by the joining of
atoms of two or more elements
Thomson (1897)

Discovered negatively charged particles




The atom was divisible!
Particles discovered are electrons
“Plum Pudding Model”
Atom consists of positively charged
material with negative charges spread
evenly throughout
Here’s JJ!
Rutherford (1908)

Gold Foil Experiment


Positive particles shot at gold foil
occasionally bounced back!
Proposed dense, positively
charged center called the
nucleus
Thomson’s theory
Rutherford’s reality
Rutherford’s atom
Bohr (1913)


Electrons move in definite orbits
around the nucleus
Places each electron in a specific
energy level
The Bohr Atom
Wave Model





Modern model based on wave mechanics
Nucleus is surrounded by electrons
Electrons do not move in orbits
We can determine the probable location of
an electron based on the amount of
energy the electron has
This probable location is called an orbital
Part Two: Subatomic particles
Three main subatomic particles



Proton
Neutron
Electron
Protons





Positively charged
Found in nucleus
Has a mass of 1 amu
The number of protons determines the
identity of the atom
The atomic number tells the number of
protons
Elements are made of atoms
Hydrogen-1proton
Helium-2 protons
Lithium-3 protons
The number of protons determines the identity
of the element!! (atomic number)
What is that other particle found in the
nucleus?


It’s a neutron!
Neutrons have no charge
–


(they’re neutral)
Neutrons have a mass of 1 amu
Proton + neutron = mass number
Electrons




Electrons hang out in “orbitals” outside the
nucleus of the atom
Electrons have almost no mass
The electron cloud is the majority of the
volume of the atom
ELECTRONS ARE NEGATIVELY
CHARGED!
More electron info!


In a neutral atom, the number of electrons is
equal to the number of protons
When an atom gains or loses electrons, it is
called an ion.
The ionization process
Now I’m a happy ion!
I’m POSITIVE! And my
outer shell is full, without that
troublesome extra electron.
This chloride ion has
added an electron. It is
a NEGATIVE ion!
(note: the inner 2
electrons are not
shown)
Now I’m a happy ion!!!
Sodium chloride-everybody’s
happy!
One lost……
(positive ion)
One gained.
(negative ion)
Quick Review:
• The three subatomic particles
are proton, neutron and
electron
• Protons are positively charged,
electrons are negative,
neutrons are neutral
• When an electron is lost or
gained, the atom becomes an
ion.
Isotopes
► Atoms
with the same number of protons but
different numbers of neutrons are called
isotopes.
► Isotopes are designated by the symbol and
the mass number:
 H-1: 1 proton, no neutrons
 H-2: 1 proton, one neutron
 H-3: 1 proton, two neutrons
It’s the Isotopes!
What symbols represent ions?
 Elements
on the left side of the
periodic table will lose electrons to
become positive ions
– Examples: Ca2+, Na+,Fe3+,Fe2+,Al3+
 Elements
on the right side of the
periodic table will gain electrons to
become negative ions
– Examples: F-, O2-, P3-, Cl-
How big is the nucleus?

If an atom was as
big as a football
field, the electrons
would move over
the entire field,
while the nucleus
would be the size
of a lima bean in
the middle of the
field.
If an atom was an elephant, the
nucleus would be as big as a flea
on the elephant
How massive is the nucleus?
 Even
though the nucleus is VERY
small, it is VERY massive. Even
though it’s the size of the flea, it
would weigh as much as the
elephant. And though the electrons
take up as much space as the
elephant, they would only weigh as
much as the flea.
Part Three: Forces Within The Atom
Forces that govern the behavior of
subatomic particles:
Strong
Weak
Electromagnetic
Gravity
Strong force
 Opposes electro-
magnetic force of
repulsion between protons
 “Glues” protons together to form
the nucleus
 Greatest of the forces, but has very
limited range
Weak force
 Responsible for radioactive
decay in the atom
Electromagnetic force
 Repels positively
charged protons
within the nucleus.
 Do you remember
the force which
holds them
together so the
atom doesn’t
explode?
 (Yes- strong
force!)
Electromagnetic force
causes proton repulsion
Strong force
overcomes
electromagnetic
Gravity
Weakest of the forces
Force of attraction between
all objects
Effect seen easily only for
very large objects