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Chapter 17 - Atomic Structure
Scientific Shorthand
•Scientists have developed their own shorthand
for dealing with long, complicated names.
•Chemical symbols
consist of one capital
letter or a capital letter
plus one or two smaller
letters.
Chemical Symbols
•Capitals matter!
•Element symbols contain ONE capital letter
followed by lowercase letter(s) if necessary.
•Scientists use two letters for some elements
because there are more elements than letters.
Metals that form
Bright blue
Co vs. CO
Solid compounds
Poisonous Gas
Atomic Components
•An element is matter that is composed of one type of
atom, which is the smallest piece of matter that still
retains the property of the element.
•Atoms are composed of particles called protons,
neutrons, and electrons
HOW DO WE KNOW THIS?
Studying Atoms
1. Ancient Greek Models of Atoms
– 400 BC
– Greek Philosopher Democritus- named
atoms(atomos)
– Believed that all matter consisted of small
particles that could not be divided and were
impossible to destroy.
– He called these particles atoms.
2. Dalton’s Atomic Theory – still use parts of
this
– John Dalton – 1803
• All elements are composed of atoms
• Atoms of the same element are alike, atoms of
different elements are different
• Compounds are formed by joining two or more of
these elements in a set ratio
Atoms of the same element
Atoms of different elements
3. Plum Pudding Model
– JJ Thomson – 1897- Plum Pudding
• Most of the atom was positively charged
• Atoms had negative charges embedded in pos.
charged material
4. Rutherford’s Model
– Ernest Rutherford – 1911- gold foil
experiment - nucleus
• Gold Foil Experiment – Rutherford fired positively
charged particles at a sheet of gold foil. Most
passed through.(like charges repel)
• Rutherford discovered the nucleus as a result of
his experiment
5. Bohr Model
– Neils Bohr – 1913
• Worked with Rutherford
• Electrons move in definite orbits
• “Orbits” are referred to as energy levels
Modern Atomic Theory
• Energy levels – the possible energies that
electrons can have
• Electrons cannot exist between energy
levels
• Electrons can move from one energy level
to another.
– when an atom gains (moves up)
– loses energy (falls to a lower level)
Electrons Losing Energy
• When an electron loses energy, it emits
light.
• Each element has a specific wavelength
and frequency at which the light is emitted.
• This gives each element a unique color.
– Example: Copper Chloride–
Sodium Chloride–
Potassium Chloride–
• We can see this through flame tests
6. Electron Cloud Model – current
Atomic Model
• Electron cloud is a visual model of the
most likely locations and motions of
electrons in atoms.
The electron cloud is
a visual model of the
probable locations of
electrons in an atom.
The probability of
finding an electron is
higher in the denser
regions of the cloud.
The Structure of the Atom
• Atoms consist of subatomic particles
– Protons
• Positive charge
• Located in the nucleus
– Neutrons
• No charge
• Located in the nucleus
– Electrons
• Negative charge
• Located in the electron cloud
Subatomic Particles
Quarks—Even
Smaller Particles
•Protons and neutrons are made up of smaller
particles called quarks.
•So far, scientists have confirmed the existence
of six uniquely different quarks
Quarks
•Scientists theorize that an arrangement of three
quarks held together with the strong nuclear force
produces a proton.
•A different arrangement of three quarks produces a
neutron
He
1. up
5. top
2. down 6. bottom
3. charm
4. strange
Finding Quarks
•To study quarks, scientists accelerate charge
particles to tremendous speeds and then force
them to collide with—or smash into—protons.
This collision causes the proton to break apart.
•The particles that result from the collision can
be detected by various collection devises.
•Atom smashers
Atomic Number and Mass Number
• Atomic Number – Identifies the element
– # of protons in the nucleus of an atom
– Different elements have different numbers of
protons
– When this number changes, you get a
different element.
• Mass Number
– Sum of an atoms protons and neutrons
– Number of neutrons = mass # - Atomic #
Isotopes
• Isotopes are atoms
of the same element
with different
numbers of neutrons
and different mass
numbers.
Nuclear Notation 
This can also be written in Hyphen
Notation  Carbon - 12
Average Atomic Mass
• The atomic mass that is on the periodic
table, is a weighted average of all of the
isotopes of a given element.
• The more abundant an isotope is, the
more heavily it counts towards the
average atomic mass.
• Example: Calculate Mass number Abundance
Si-28
92.21 %
the average atomic
Si-29
4.70 %
Mass.
Si-30
3.09 %
Atomic Orbitals
• Orbital is a region of space around the
nucleus where an electron is likely to be
found.