S-105
• Describe the mass, charge, and location of
protons, neutrons, and electrons in atoms.
Chapter 4
Atomic Structure
SPS1 Students will investigate our current understanding of the atom.
a.
Examine the structure of the atom in terms of
-
proton, electron, and neutron locations
Atomic mass and atomic number
Atoms with different numbers of neutrons (isotopes)
Explain the relationship of the proton number to the elements identity
4.1 Studying Atoms
What was Dalton’s theory of the structure of matter?
What contributions did Thomson and Rutherford make
to the development of atomic theory?
4.1 Studying Atoms
What was Dalton’s theory of the structure of matter?
• Democritus – (Greek) all matter is
composed of small particles that can not be
divided
– Called atoms (uncut or indivisible)
– Thought atoms had different shapes
• Liquids – round and smooth
• Solids – rough and prickly
• Aristotle – (Greek) matter could be divided
forever
– Five elements (earth, water, air, fire, aether)
4.1 Studying Atoms
What was Dalton’s theory of the structure of matter?
• John Dalton (England, 1700’s)
– Noticed that elements in compounds always
came in specific ratios
• Water – 8 oxygen to 1 hydrogen
– Developed a theory to explain
4.1 Studying Atoms
What was Dalton’s theory of the structure of matter?
• Dalton’s Atomic Theory
– All elements are composed of atoms
– All atoms of the same element have the same
mass, and atoms of different elements have a
different mass
– Compounds are composed of atoms of one or
more elements
– For a specific compound, atoms of different
elements combine in exactly the same way
4.1 Studying Atoms
What contributions did Thomson and Rutherford make to the development
of atomic theory?
• Thomson’s Model of the Atom
Simulation
– Cathode Ray Experiment
– Beams moved toward positive, and away from
the negative
• Particles must be negative (electrons)
– Atoms are neutral, so there must also be positive
particles
• Plum Pudding Model – electrons are evenly
scattered in a positively charged mass
4.1 Studying Atoms
What contributions did Thomson and Rutherford make to the development
of atomic theory?
• Rutherford’s Atomic Theory
Simulation
– The gold foil experiment
– Alpha particles (helium nucleus) shot at gold foil
• Most particles passed through the gold
• Some bounced back as if they had run into something
• Conclusion
– The atom has a very small, dense nucleus of
positive charge (nucleus)
– Electrons exist in the rest of the space
S-106
• List the four postulates of Dalton’s Atomic
Theory.
S-107
• In the history of the study of the atom,
what did each of the following do
• Democritus
• JJ Thomson
• Rutherford
4.2 The Structure of the Atom
What are three subatomic particles?
How are atoms of one element different from atoms of another
element?
What is the difference between two isotopes of the same element?
4.2 The Structure of the Atom
What are the three subatomic particles?
• Subatomic Particles
– Proton – (Rutherford)
• Positively charged
• In the nucleus
• Relative mass is 1
4.2 The Structure of the Atom
What are the three subatomic particles?
• Subatomic Particles
– Electron – (Thomson)
• Negatively charged
• Outside of the nucleus (electron cloud)
• Relative mass is 1/1836 – so 0
4.2 The Structure of the Atom
What are the three subatomic particles?
• Subatomic Particles
– Neutron – (James Chadwick 1932)
• Neutral or no charge
• In the nucleus
• Relative mass is 1
4.2 The Structure of the Atom
How are atoms of one element different from atoms of other elements?
• Dalton – atoms of one element are different
from atoms of another
– Atomic Number
• Atoms of the same element have the same number of
protons
• Atoms of different elements have different numbers of
protons
• The number of protons is give by the Atomic Number
4.2 The Structure of the Atom
How are atoms of one element different from atoms of other elements?
• Dalton – atoms of one element are different
from atoms of another
– Mass Number
• The sum of the protons and neutrons in a atom
• Or neutrons = mass number – atomic number
• Periodic tables list the average atomic mass
4.2 The Structure of the Atom
What is the difference between two isotopes of the same element?
• Atoms of the same element have the same
atomic number, but don’t necessarily have
the same mass number
– Isotope
•
•
•
•
Of the same element
Same number of protons
Different neutrons so the mass number is different
Listed by element name and mass number
– Uranium – 238
• Basically no difference in chemical properties
S-108
• List the atomic number, mass number,
number of protons, neutrons, electrons, and
the name of the following elements.
S-109
• There are three naturally occurring isotopes
of Uranium, Uranium -238, Uranium -235,
Uranium -234.
• In terms of subatomic particles, what is the
same about these three?
• What is different?
4.3 Modern Atomic Theory
What can happen to electrons when atoms gain or lose energy?
What model do scientists use to describe how electrons behave in
atoms?
What is the most stable configuration of electrons in an atom?
4.3 Modern Atomic Theory
What can happen to electrons when atoms gain or lose energy?
• Bohr Model
– The rest of models discuss location of electrons
– Bohr believed that electrons orbit around the
nucleus
– Constant speed, fixed orbit
– Energy levels – higher energy electrons were
further away from the nucleus
• Energy was lost or gained to move between levels
• Limited number of electrons were allowed in each
energy level
4.3 Modern Atomic Theory
What model do scientists use to describe how electrons behave in atoms?
• Electron Cloud Model
– Different energy levels
– Represented by areas of probability
• Areas become larger with energy
• Electrons can be anywhere in the probability area
– Orbital – probability area for a specific amount
of energy
• Called s, p, d, f
• Energy levels hold 2, 8, 18, 32 electrons maximum
4.3 Modern Atomic Theory
What model do scientists use to describe how electrons behave in atoms?
• Electron Configuration
– The way the electrons are arranged in different
orbitals
– Most stable when the electrons are in the lowest
possible energy states
– This is called the Ground State
S-110
• What idea did Neil’s Bohr present in his
planetary model of the atom.
• What idea from the Bohr model was kept in
the electron cloud model.
• What was different?
S-111
•
A.
B.
C.
D.
An atom has 22 protons and 28 neutrons
What is its atomic number?
What is the name of the element?
What is the symbol of the element?
What is the average
atomic mass of the
element?
E. What is the atomic
mass of this atom?
S-112
We have a test!
We have a test!
La La La La La!