3. Democritus 400 BC • 1st idea of “atoms”
Greece - stated that
all matter is made up
• Believed all matter is made
of atoms. He also
stated that atoms are up of tiny particles separated
eternal and invisible
and so small that
they can’t be divided,
by space
and they entirely fill
up the space they’re
• Called particles “atomos”
in
which means indivisible.
Lavoisier 1789 • Founder of modern
chemistry
France - provided the
formula for the
conservation of matter
• 1st carefully controlled
in chemical reactions,
and also distinguished experiments providing
between an element
and a compound evidence to the Law of
Conservation of Mass
4. Dalton 1766-1844 1st MODERN Atomic Theory
England - formed the 1st
1.All matter made up of tiny
atomic theory, which states
that all matter is composed of indivisible particles called atoms
tiny, indestructible particles
called atoms that are all alike 2.Atoms of the same element
and have the same atomic
weight. have identical properties
3.Atoms of different elements
have different properties
4.Atoms combine in a specific
ratio to form compounds
5.A specific compound is always
made up of atoms in a specific
proportion.
5. Thomson 1897 Plum Pudding Model
1.Negative particles scrambled
into the “dough” of the positive
particles.
England - discovered
the electron and
developed the plum-
pudding model of the
atom.
Rutherford 1898 Gold Foil Experiment
England - used the
results of his gold-foil
1.Atoms are mostly empty
experiment to state that
all the mass of an
space
atom was in a small
positively-charged 2.All the Mass of an atom is in
ball at the center of
the atom. the positively charged ball in the
center of the structure.
6. Rutherford Continued
• Top(RED): Expected results: alpha particles passing through
the plum pudding model of the atom undisturbed.
Bottom (YELLOW): Observed results: a small portion of the
particles were deflected, indicating a small, concentrated
positive charge. Note that the image is not to scale; in reality
the nucleus is vastly smaller than the electron shell
7. Bohr 1922 Denmark - stated that
“Planetary” atom model
the electrons moved 1.Believed the atom structure was like our
around the nucleus in
successively large solar system
orbits. He also
presented the Bohr
2.Nucleus in the middle like the sun and
atomic model which the electrons orbiting like the planets.
stated that atoms
absorb or emit radiation
only when the electrons
abruptly jump between
allowed, or stationary,
states.
Schroedinger 1930 Wave Mechanic Model
Austria - introduced the
Shroedinger Equation, a 1.Planetary model was too specific
wave equation that
describes the form of the
2.Rather: electrons vibrate around the
probability waves that
govern the motion of
outside of the nucleus- can only
small particles and how
these waves are altered
predict where they are most like to be
by external influences. 3.QUARKS – protons, neutrons and
electrons made up of some of these
smaller particles.
4.http://library.thinkquest.org/05aug/01087/quarks.html
8. Basic Atomic Structure Today scientist agree on the
three basic subatomic particles
that make up all atoms.
Bohr Model for Lithium
(not to scale) Electron = 3
P= 3 +
N = 3 0
Where is most of the mass in the NUCLEUS
Atom?
Where is most of the volume in the Outside the Nucleus; Electron
Atom?
Cloud
9. Nucleus • Contains protons(+) and
Neutrons (0)
• Holds most of the mass of
the atom
• Very small compared to the
entire size of the atom
• Most dense part of the atom
Electron • Negatively charged
subatomic particle
• Found outside the nucleus in
the electron cloud
• Smallest particle; mass =
1/1836th of the atom
10. • Positively charged subatomic particle
Proton • Found in the nucleus
• Mass = 1 amu (atomic mass unit)
• # of protons in an atom IDENTIFIES the
atom (which element)
• Each element has its own unique # of
protons- change the proton count:
change the element
• # of protons in the nucleus of an atom
called the atomic number
Neutron • Zero charge
• Mass = 1 amu
• Do NOT affect the identity of the atom
• Found in the nucleus
• Same atom of an element can have
varying amounts of neutrons (isotope)
• Adding the total number of protons &
neutrons = Atomic Mass Number
http://www.sawyerscience.com/Units/unit2/atoms_compounds.html
11. • Atomic Number :
• # of protons
3
• # of electrons if atom is neutrally
Li •
charged
Chemical Symbol:
Lithium
• Element abbreviation
6.9 • Some based on Latin names
• Element Name:
• There in case you forget
• Atomic Mass:
• Sum of the particles in the nucleus
(protons & neutrons)
• Can change with isotopes of the same
element
• Represents an AVERAGE MASS
Isotope
Same # of protons (same element); different #
of neutrons
Ion
Charged particle; electrons vary
