Download Atomic Structure

NOTES 4 – Atomic Structure
The Idea of the Atom

Democritus (~400 BC)
• Greek philosopher
• “All matter is made of tiny, indivisible
particles”

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A tomos means unable to be divided
Democritus thought atoms were the
smallest pieces of matter
The Development of the Modern
Atomic Model

John Dalton (1803)
• Each element has different size and
shape atoms
• Atoms of different elements combine to
form compounds

JJ Thompson (1897)
• Atoms are solid masses of smaller
charged particles, half are positive and
half are negative
The Development of the Modern
Atomic Model

Ernst Rutherford (1905)
• Gold Foil Experiment
• Most of the atom is empty space
• There is a tiny bunch of positively charged
particles in the center of an atom
The Gold Foil Experiment
The Development of the Modern
Atomic Model

Niels Bohr (1911)
• Negatively charged
particles orbit the
bunch of positively
charged particles
• The orbiting,
negative particles
are organized into
energy levels
The Modern Atomic Model
The Modern Atomic Model
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Subatomic particles – tiny
particles that make up atoms
There are three types of subatomic
particles:
1. Protons (p+) – positively charged
particles
2. Neutrons (n0) – particles with no
charge
3. Electrons (e-) – negatively charged
particles
Nucleus

Nucleus - the dense center part of
the atom
• Contains the protons and neutrons
• Nucleus contains 99.99% of the mass of
an atom
• Electrons orbit nucleus
Atoms are extremely small
Comparing Subatomic Particles
Particle
Location
Size & Mass
Charge
Proton (p+)
Nucleus
Equal to
Neutron
Positive (+)
Neutron (n0)
Nucleus
Equal to Proton
Neutral (0)
Electron (e-)
10,000X smaller
Outside Nucleus
than protons Negative (-)
and neutron
Atoms are Neutral

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Every atom has equal numbers of
protons (p+) and electrons (e-)
Ex. Oxygen atoms have 8 p+ and 8 eThe negatives cancel out the
positives
• 8 protons
• 8 electrons
• Total charge
=
=
=
+ 8 charge
- 8 charge
0
Count the protons and electrons in
this fluorine atom
Electrons in Energy Levels


Electrons surround
the nucleus in
energy levels
The number of
energy levels
depends on how
many electrons the
atom has
How Many Electrons in Each Level?

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1st energy level holds 2 e2nd energy level holds up to 8 e3rd energy level holds up to 18 eAtoms with 2 e- or less have 1 energy
level
Atoms with 3 to 10 e- have 2 energy
levels
Atoms with more than 10 e- have at least
3 energy levels
Valence Electrons


Valence electrons - The electrons in the
outer most energy level
Valence electrons determine the reactivity
of an atom
• Will it bond with other atoms?

Ex. Oxygen atoms have 8 electrons
• 2 in the first level
• 6 in the second level
• How many valence e- does an oxygen atom
have?
 6
The periodic table gives information
about 1 atom of any element
The periodic table gives information
about 1 atom of any element
The periodic table gives information
about 1 atom of any element
The periodic table gives information
about 1 atom of any element
The periodic table gives information
about 1 atom of any element
The periodic table gives information
about 1 atom of any element

Atomic Number = Number of protons &
electrons
• Ex. 1 oxygen atom has 8 protons and 8 electrons

Mass Number = Number of protons + neutrons
• Ex. 1 oxygen atom has 16 protons + neutrons
• To figure out the # of neutrons, subtract the atomic
number from the mass number
• 16 – 8 = 8 so an oxygen atom has 8 neutrons
How many protons, neutrons, and electrons
are in one atom of sodium?

Atomic number is
11, so there are:
• 11 protons
• 11 electrons

Mass number is 23,
so there are:
• 23 – 11 = 12
• 12 neutrons