Download Chapter 10 Section 1 Development of the Atomic Theory

Chapter 10
Section 1 Development of the
Atomic Theory
Question of the Day
In your own words write your definition of the following
terms:
•Element
•Compound
•Mixture
•Atom
Chapter 10
Introduction to Atoms
Preview
Section 1 Development of the Atomic Theory
Section 2 The Atom
Chapter 10
Section 1 Development of the
Atomic Theory
Objectives
• Describe some of the experiments that led to the
current atomic theory.
• Compare the different models of the atom.
• Explain how the atomic theory has changed as
scientists have discovered new information about the
atom.
Chapter 10
Section 1 Development of the
Atomic Theory
The Beginning of the Atomic TheoryA LONG TIME AGO!!!!
• What Is an Element? Greek philosopher named
Democritus thought that you cut something in half over
and over that you would eventually end up with a
particle that could not be cut.
•He called this particle an atom.
• From Aristotle to Modern Science Aristotle,
another Greek philosopher, disagreed with
Democritus’s ideas. He believed that you would never
end up with a particle that could not be cut.
Chapter 10
Section 1 Development of the
Atomic Theory
The Beginning of the Atomic TheoryA LONG TIME AGO!!!
• Who was right?
•Democritus was right.
•Matter is made of particles, which we call atoms.
• An atom is the smallest unit of an element that
maintains the chemical properties of that element.
Chapter 10
Section 1 Development of the
Atomic Theory
NOT SO LONG AGO!!!
Dalton’s Atomic Theory Based on Experiments
• Dalton’s Theory John Dalton published his atomic
theory in 1803. His theory stated that all substances
are made of atoms.
• Atoms are small particles that cannot be created,
divided, or destroyed.
• Atoms of the same element are exactly alike, and
atoms of different elements are different. Just like you
are!
• Atoms join with other atoms to make new
substances. Just like in compounds and mixtures.
Chapter 10
Section 1 Development of the
Atomic Theory
NOT SO LONG AGO!!!
Thomson’s Discovery of Electrons
• Negatively Charged Particles Thomson
experimented with a cathode-ray tube. He discovered
negatively charged particles that are now known as
electrons.
• Like Fruit in Jello After learning that atoms contain
electrons Thompson thought that electrons were mixed
throughout an atom, like fruit in jello.
Chapter 10
Section 1 Development of the
Atomic Theory
Chapter 10
Section 1 Development of the
Atomic Theory
GETTING CLOSER!!!
Rutherford’s Atomic “Shooting Gallery”
• In 1909, Ernest Rutherford aimed a beam of small,
positively charged particles at a thin sheet of gold foil.
The next slide shows his experiment.
• Surprising Results Rutherford expected the
particles to pass right through the gold in a straight
line. To Rutherford’s great surprise, some of the
particles were deflected.
Chapter 10
Section 1 Development of the
Atomic Theory
Chapter 10
Section 1 Development of the
Atomic Theory
Where Are the Electrons?
• Far from the Nucleus
Rutherford proposed that: In
the center of the atom is a tiny,
positively charged part called
the nucleus.
• Bohr’s Electron Levels In
1913, Niels Bohr proposed that
electrons move around the
nucleus in certain paths, or
energy levels.
Chapter 10
Section 1 Development of the
Atomic Theory
Where Are the Electrons?, continued
• The Modern Atomic
Theory According to the
current theory, there are
regions inside the atom
where electrons are likely
to found. These regions
are called electron
clouds.
Chapter 10
Section 1 Development of the
Atomic Theory
Comparing Models of the Atom
Click below to watch the Visual Concept.
Visual Concept
Chapter 10
Section 2 The Atom
Question of the Day
Answer the following question: An atom is the smallest
particle into which an element can be divided and still
be that element. Now that scientists have learned that
an atom is made up of even smaller particles, is this
definition still accurate?
Write down your answer.
Chapter 10
Section 2 The Atom
Objectives
• Describe the size of an atom.
• Name the parts of an atom.
• Describe the relationship between numbers of
protons and neutrons and atomic number.
• State how isotopes differ.
• Calculate atomic masses.
• Describe the forces within an atom.
Chapter 10
Section 2 The Atom
How Small Is an Atom?
• Three One-Hundred-Millionths of a Centimeter!
Scientists know that aluminum is made of averagesized atoms. An aluminum atom has a diameter of
about 0.00000003 cm.
Chapter 10
Section 2 The Atom
What Is an Atom Made Of?
• The Nucleus
•Protons are positively charged particles in the
nucleus.
•Neutrons are the particles of the nucleus that have
no electrical charge.
• Outside the Nucleus
•Electrons are the negatively charged particles in
atoms.
•Electrons are found around the nucleus within
electron clouds. All the structures of the atom can be
seen on the next slide.
Chapter 10
Section 2 The Atom
Chapter 10
Section 2 The Atom
How Do Atoms of Different Elements Differ?
• Starting Simply The
hydrogen atom has one
proton and one electron.
• Now for Some
Neutrons The helium
atom has two protons, two
neutrons, and two
electrons.
Chapter 10
Section 2 The Atom
How Do Atoms of Different Elements Differ?
• Building Bigger Atoms For bigger atoms, simply
add protons, neutrons, and electrons.
• Protons and Atomic Number
•The number of protons in the nucleus is the atomic
number of that atom.
•All atoms of an element have the same atomic
number.
Chapter 10
Section 2 The Atom
Isotopes
• Isotopes are atoms that have the same number of
protons but have different numbers of neutrons.
Chapter 10
Section 2 The Atom
Isotopes, continued
• Properties of Isotopes
•An unstable atom is an atom with a nucleus that will
change over time. This type of isotope is radioactive.
• Telling Isotopes Apart
•You can identify each isotope of an element by its
mass number. The mass number is the sum of the
protons and neutrons in an atom.
Chapter 10
Section 2 The Atom
Isotopes, continued
Chapter 10
Section 2 The Atom
Isotopes, continued
• Naming Isotopes
• To name a specific isotope of an element, write the
name of the element followed by a hyphen and the
mass number of the isotope. E.g. Uranium-235 and
Uranium-238.
• Calculating the Mass of an Element
•The atomic mass of an element is the weighted
average of the masses of all the naturally occurring
isotopes of that element.
Chapter 10
Section 2 The Atom
Chapter 10
Section 2 The Atom
Forces in Atoms
• Four Basic Forces Four basic forces are at work
everywhere, even within the atom. These forces are
gravitational force, electromagnetic force, strong force,
and weak force.
• These forces work together to give an atom its
structure and properties.
Chapter 10
Section 2 The Atom