Warm Up

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Draw diagrams of J.J. Thomson’s and Rutherford’s models of the atom and record the differences.

Warm Up

9/1/2011

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Lesson 1-6

• Niels Bohr proposed that electrons

move in circular orbits, or energy levels, around the nucleus.

• Electrons closer to the nucleus have

less energy than electrons farther away from the nucleus.

Bohr’s Atomic Model

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Lesson 1-6

• More research showed that, although electrons have specific amounts of

energy, energy levels are not arranged in circular orbits.

• When an electron moves from a higher energy level to a lower energy level,

energy is released—sometimes as visible light.

Bohr’s Atomic Model

^(cont.)

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Lesson 1-6

In Bohr’s model of the atom, electrons move in circular orbits around the atom.

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Lesson 1-6

Bohr’s Atomic Model

^(cont.)

How did Bohr’s model of the atom differ from Rutherford’s?

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Lesson 1-6

• In the modern atomic model, electrons form an electron cloud.

• An electron cloud is an area around an atomic nucleus where an electron is

most likely to be.

The Modern Atomic Model

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Lesson 1-6

In this atom, electrons are more likely to be found closer to the nucleus than farther away.

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Lesson 1-6

The Modern Atomic Model

^(cont.)

How has the model of the atom changed over time?

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Lesson 1-6

• Protons and neutrons are made of smaller particles called quarks.

• Scientists theorize that there are six types of quarks: up, down, charm, strange, top, and bottom.

.

Quarks

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Lesson 1 - VS

• If you were to divide an element into smaller and smaller pieces, the

smallest piece would be an atom.

• Atoms are so small that they can be seen only by using very powerful

microscopes.

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Lesson 1 - VS

• Scientists now know that atoms contain a dense, positive nucleus surrounded by an electron cloud.

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Lesson 1 - Now

1. The earliest model of an atom

contained only protons and electrons.

2. Air fills most of an atom.

3. In the present-day model of the atom, the nucleus of the atom is at the center of an electron cloud.

Do you agree or disagree?

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End of

Day

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Lesson 2 Reading Guide - KC

• What happens during nuclear decay?

• How does a neutral atom change

when its number of protons, electrons, or neutrons changes?

Protons, Neutrons, and

Electrons—How Atoms Differ

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Lesson 2 Reading Guide - Vocab

• atomic number

• isotope

• mass number

• average atomic mass

Protons, Neutrons, and

Electrons—How Atoms Differ

• radioactive

• nuclear decay

• ion

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Lesson 2-1

• The mass of electrons is much smaller than the mass of protons or neutrons.

• Most of the mass of an

atom is found in the nucleus.

The Parts of the Atom

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Lesson 2-1

• The number of protons in an atom of an element is the element’s atomic

number.

• The atomic number is the whole number listed with each element on the periodic table.

• Atoms of different elements contain different numbers of protons.

Different Elements—Different

Numbers of Protons

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Lesson 2-1

Different elements have different atomic numbers.

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Lesson 2-1

• Neutral atoms of different elements also have different numbers of electrons.

• In a neutral atom, the number of

electrons equals the number of protons;

therefore, the number of positive charges equals the number of negative charges.

Different Elements—Different

Numbers of Protons

^(cont.)

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Lesson 2-2

• Atoms of the same element can have different numbers of neutrons.

• Isotopes are atoms of the same element that have different numbers of neutrons.

• Most elements have several isotopes.

Neutrons and Isotopes

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Lesson 2-2

Neutrons and Isotopes

^(cont.)

isotope

from Greek isos, means “equal”;

and topos, means “place”

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Lesson 2-2

• The mass number of an atom is the sum of the number of protons and

neutrons in an atom.

Mass number = number of protons + number of neutrons

• An isotope is often written with the element name followed by the mass number.

Neutrons and Isotopes

^(cont.)

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Lesson 2-2

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Lesson 2-2

The average atomic mass of an element is the average mass of the element’s isotopes,

weighted according to the abundance of each isotope.

Neutrons and Isotopes

^(cont.)

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Lesson 2-4

• Marie Curie called elements that spontaneously emit radiation

radioactive.

• Henri Becquerel and Pierre and Marie Curie discovered that the radiation

released by uranium was made of energy and particles.

Radioactivity

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Lesson 2-4

• This radiation came from the nuclei of the uranium atoms.

• When uranium releases radiation, it changes to a different element.

Radioactivity

^(cont.)

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Lesson 2-4

• Nuclear decay is a process that occurs when an unstable atomic nucleus

changes into another more stable nucleus by emitting radiation.

• Nuclear decay can produce three different types of radiation—alpha

particles, beta particles, and gamma rays.

Radioactivity

^(cont.)

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Lesson 2-4

An alpha particle is made of two protons and two neutrons. When an atom releases an

alpha particle, its atomic number decreases by two.

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Lesson 2-4

When beta decay occurs, a neutron changes into a proton and a high-energy electron

called a beta particle. The atomic number of an atom increases by one because it has gained a proton.

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Lesson 2-4

Because gamma rays do not contain

particles, the release of gamma rays does not change one element into another

element.

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Lesson 2-4

Radioactivity

^(cont.)

What happens during radioactive decay?

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Lesson 2-4

• The energy released by radioactive

decay can be both harmful and beneficial to humans.

• Radiation therapy can be beneficial to

humans by destroying harmful cells such as cancer cells.

Radioactivity

^(cont.)

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Lesson 2-5

• An ion is an atom that is no longer neutral because it has gained or lost electrons.

• An ion can be positively or negatively charged depending on whether it has lost or gained electrons.

Ions—Gaining or Losing Electrons

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Lesson 2-5

• When a neutral atom loses one or more electrons, it has more protons than

electrons and as a result, has a positive charge.

• An atom with a positive charge is called a positive ion.

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Lesson 2-5

• When a neutral atom gains one or more electrons, it now has more electrons than protons and as a result, has a negative charge.

• An atom with a negative charge is called a negative ion.

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Lesson 2-4

Ions—Gaining or Losing Electrons

(cont.)

How does a neutral atom change when its number of protons or

electrons changes?

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Lesson 2 - VS

• Different elements contain different numbers of protons.

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Lesson 2 - VS

• Two isotopes of a given element

contain different numbers of neutrons.

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Lesson 2 - VS

• When a neutral atom gains or loses an electron, it becomes an ion.

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Lesson 2 – LR1

A. electrons B. neutrons C. nucleus D. protons

Where is most of the mass of an atom found?

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Lesson 2 – LR2

A. atomic number

B. average atomic mass C. isotope

D. mass number

Which term refers to the sum of the number of protons and neutrons in an atom?

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Lesson 2 – LR3

A. ion

B. isotopes

C. nuclear decay D. radioactive

What term did Marie Curie use to describe elements that

spontaneously emit radiation?

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Lesson 2 - Now

4. All atoms of the same element have the same number of protons.

5. Atoms of one element cannot be changed into atoms of another element.

6. Ions form when atoms lose or gain electrons.

Do you agree or disagree?

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Chapter Review Menu

Key Concept Summary Interactive Concept Map Chapter Review

Standardized Test Practice

(45)

The BIG Idea

An atom is the smallest unit of an element and is made mostly of

empty space. It

contains a tiny nucleus surrounded

by an electron cloud.

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Key Concepts 1

• If you were to divide an element into smaller and smaller pieces, the smallest piece would be an atom.

• Atoms are so small that they can be seen only by powerful scanning microscopes.

• The first model of the

atom was a solid sphere.

Now, scientists know that an atom contains a dense positive nucleus

surrounded by an electron cloud.

Lesson 1: Discovering Parts of the Atom

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Key Concepts 2

Lesson 2: Protons, Neutrons, and Electrons—How Atoms Differ

• Nuclear decay occurs when an unstable atomic nucleus changes into another more stable nucleus by emitting radiation.

• Different elements contain different numbers of protons.

Two isotopes of the same element contain different

numbers of neutrons. When a neutral atom gains or loses an electron, it becomes an ion.

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Chapter Review – MC1

A. atom

B. electron C. neutron D. proton

Which term describes a neutral particle that exists in the nucleus of an atom?

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A. Thomson B. Rutherford C. Chadwick D. Bohr

Who discovered that, in addition to protons, the nucleus also

contained neutrons?

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A. electron cloud B. isotope

C. nucleus D. quarks

Protons and neutrons are made of smaller particles called what?

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A. radiation

B. radioactivity

C. nuclear decay

D. radiation therapy

Which term refers to the process that occurs when an unstable

atomic nucleus changes into another more stable nucleus by emitting radiation?

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A. positive ion B. negative ion C. isotope

D. quarks

Which describes an atom with a positive charge?

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Chapter Review – STP1

A. quark B. nucleus C. electron D. atom

Which term refers to the smallest piece of an element that still

represents that element?

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A. Aristotle B. Bohr

C. Chadwick D. Rutherford

Who concluded that most of an atom’s mass and positive charge is concentrated in the nucleus?

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A. proton B. nucleus C. neutron D. electron

Which is an atomic particle that has one positive charge?

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A. ion

B. isotope C. neutron D. proton

Which term refers to an atom that is no longer neutral because it

has gained or lost electrons?

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A. atomic number B. mass number C. relative mass

D. average atomic mass

Which refers to the average mass of an element’s isotopes,

weighted according to the abundance of each isotope?