CHAPTER 4

Matter – Properties and Change

National Standards for Chapter 4

– UCP.2 Evidence, models, and explanation– A.1 Abilities necessary to do scientific inquiry– B.1 Structure of atoms– B.2 Structure and properties of matter

Vocabulary/Study Guide

• Define each term using the Glossary• Either write on the handout, or use your own

paper• This is due on Test Day (tentatively, Friday,

October 11)

Section 1: Early Ideas About Matter

• National Standards:– UCP.2 Evidence, models, and explanation– A.1 Abilities necessary to do scientific inquiry– B.1 Structure of atoms– B.2 Structure and properties of matter

Objectives – Section 1

• Compare and contrast the atomic models of Democritus, Aristotle, and Dalton.

• Understand how Dalton's theory explains the conservation of mass.

REVIEW VOCABULARY:• theory: an explanation supported by many experiments; is

still subject to new experimental data, can be modified, and is considered successful if it can be used to make predictions that are true

New Vocabulary

Dalton’s atomic theory

• The ancient Greeks tried to explain matter, but the scientific study of the atom began with John Dalton in the early 1800's.

Early Ideas About Matter

• Many ancient scholars believed matter was composed of such things as earth, water, air, and fire.

• Many believed matter could be endlessly divided into smaller and smaller pieces.

Early Ideas About Matter

• Democritus (460–370 B.C.) was the first person to propose the idea that matter was not infinitely divisible, but made up of individual particles called atomos, from which the English word atom is derived.

• Aristotle (484–322 B.C.) disagreed with Democritus because he did not believe empty space could exist.

• Aristotle’s views went unchallenged for 2,000 years until science developed methods to test the validity of his ideas.

Early Ideas About Matter

Early Ideas About Matter

• John Dalton revived the idea of the atom in the early 1800s based on numerous chemical reactions.

• Dalton’s atomic theory easily explained conservation of mass in a reaction as the result of the combination, separation, or rearrangement of atoms.

Early Ideas About Matter

Early Ideas About MatterAncient Greeks

• Matter is composed of atoms, which move through empty space

• Atoms are solid, homogeneous, indestructible, and indivisible

• Different kinds of atoms have different sizes and shapes

• Size, shape, and movement of atoms determine the properties of matter

John Dalton• Matter is composed of extremely

small articles called atoms• Atoms are indivisible and

indestructible• Atoms of a given element are

identical in size, mass, and chemical properties

• Atoms of a specific element are different from those of another element

• Different atoms combine in simple whole-number ratios to form compounds

• In a chemical reaction, atoms are separated, combined, or rearranged

Homework, Section 1

• SECTION 1 REVIEW, Page 105• Questions #1, 4-6• Answer with complete sentences• Finish filling in charts that were handed out in

class: Compare and contrast early ideas of the atom vs. John Dalton’s ideas of the atom

• Due tomorrow

Section 2: Changes in Matter

• National Standards:– UCP.2 Evidence, models, and explanation– B.1 Structure of atoms– B.2 Structure and properties of matter

Objectives – Section 2

• Define atom.

• Distinguish between the subatomic particles in terms of relative charge and mass.

• Describe the structure of the atom, including the locations of the subatomic particles.

Review Vocabulary:• model: a visual, verbal, and/or mathematical explanation of

data collected from many experiments

New Vocabulary

• atom nucleus• cathode ray proton• electron neutron

• An atom is made of a nucleus containing protons and neutrons; electrons move around the nucleus.

The Atom

• The smallest particle of an element that retains the properties of the element is called an atom.

• An instrument called the scanning tunneling microscope (STM) allows individual atoms to be seen.

The Electron

• When an electric charge is applied, a ray of radiation travels from the cathode to the anode, called a cathode ray.

• Cathode rays are a stream of particles carrying a negative charge.

• The particles carrying a negative charge are known as electrons.

The Electron

• This figure shows a typical cathode ray tube.

The Electron

• J.J. Thomson measured the effects of both magnetic and electric fields on the cathode ray to determine the charge-to-mass ratio of a charged particle, then compared it to known values.

• The mass of the charged particle was much less than a hydrogen atom, then the lightest known atom.

• Thomson received the Nobel Prize in 1906 for identifying the first subatomic particle—the electron

The Electron

• In the early 1910s, Robert Millikan used the oil-drop apparatus shown below to determine the charge of an electron.

The Electron

• Charges change in discrete amounts—1.602 10–19 coulombs, the charge of one electron (now equated to a single unit, 1–).

• With the electron’s charge and charge-to-mass ratio known, Millikan calculated the mass of a single electron.

the mass of a hydrogen atom

Transparency 11: Cathode Ray Experiments

The Electron

• Matter is neutral. You know that matter is neutral from everyday experiences. You do not receive an electric shock (except under certain conditions) when you touch an object.

• If electrons are negative, then how is matter, which is made up of electrons, neutral?

• J.J. Thomson proposed a model of the atom to answer this question.

The Electron

• J.J. Thomson's plum pudding model of the atom states that the atom is a uniform, positively charged sphere containing electrons.

The Nucleus

• In 1911, Ernest Rutherford studied how positively charged alpha particles interacted with solid matter.

By aiming the particles at a thin sheet of gold foil, Rutherford expected the paths of the alpha particles to be only slightly altered by a collision with an electron.

The Nucleus

• Although most of the alpha particles went through the gold foil, a few of them bounced back, some at large angles.

The Nucleus

• Rutherford concluded that atoms are mostly empty space.

• Almost all of the atom's positive charge and almost all of its mass is contained in a dense region in the center of the atom called the nucleus.

• Electrons are held within the atom by their attraction to the positively charged nucleus.

The Nucleus

• The repulsive force between the positively charged nucleus and positive alpha particles caused the deflections.

The Nucleus

• Rutherford refined the model to include positively charged particles in the nucleus called protons.

• James Chadwick received the Nobel Prize in 1935 for discovering the existence of neutrons, neutral particles in the nucleus which accounts for the remainder of an atom’s mass.

Transparency 12: Understanding Rutherford’s Gold Foil Experiment

The Nucleus

• All atoms are made of three fundamental subatomic particles: the electron, the proton, and the neutron.

• Atoms are spherically shaped.

• Atoms are mostly empty space, and electrons travel around the nucleus held by an attraction to the positively charged nucleus.

The Nucleus

• Scientists have determined that protons and neutrons are composed of subatomic particles called quarks.

The Nucleus

• Scientists do not yet understand if or how quarks affect chemical behavior.

• Chemical behavior can be explained by considering only an atom's electrons.

Homework, Section 2

• SECTION 2 REVIEW, Page 114• Questions #7-11 – Answer with complete

sentences• Due tomorrow

Section 3: How Atoms Differ

• National Standards:– B.1 Structure of atoms

Objectives – Section 3

• Explain the role of atomic number in determining the identity of an atom.

• Define an isotope.

• Explain why atomic masses are not whole numbers.

• Calculate the number of electrons, protons, and neutrons in an atom given its mass number and atomic number.

Review Vocabulary:• substance: a form of matter that has a uniform and unchanging

composition; also known as a pure substance

New Vocabulary

• atomic number mass number• isotopes atomic mass

atomic mass unit (amu)

• The number of protons and the mass number define the type of atom.

Review Vocabulary• periodic table: a chart that organizes all known elements into

a grid of horizontal rows (periods) and vertical columns (groups or families) arranged by increasing atomic number

Atomic Number

• Each element contains a unique positive charge in their nucleus.

• The number of protons in the nucleus of an atom identifies the element and is known as the element’s atomic number.

Transparency 3: The Periodic Chart

Atomic Number

• Practice Problems #12-15 on Page 116– Write the problem, then the answer– Use the same paper as Transparency 3: The

Periodic Chart

Periodic Table (pg. 116 TE)Dmitri Mendeleev (pg. 85)

• Classification based on the similarities and masses of the elements

• Observed periodic patterns in the properties of the elements

• Eight columns with up to seventeen elements in each column

• Many missing elements

Henry Moseley (pg. 115)

• Each element has a unique positive charge in its nucleus

• Used X-rays to calculate the size of the nucleus

• Organized left-to-right and top-to-bottom by increasing atomic number

• Horizontally – 7 periods Vertically – 8 families

Isotopes and Mass Number

• All atoms of a particular element have the same number of protons and electrons but the number of neutrons in the nucleus can differ.

• Atoms with the same number of protons but different numbers of neutrons are called isotopes.

Isotopes and Mass Number

• In nature, most elements are found as mixtures of isotopes. Usually, the relative abundance of each isotope is constant.– Ex. In a banana, 93.26% is potassium-39, 6.73% is

potassium-41 and 0.01% is potassium-40. In another banana or in a different source of potassium, the percentage composition of the potassium isotopes will still be the same.

• Isotopes containing more neutrons have a greater mass.• Isotopes of an atom have the same chemical behavior.

Isotopes and Mass Number

• The mass number is the sum of the protons and neutrons in the nucleus.

Transparency 13: Isotopes

Isotopes and Mass Number

• Practice problems #16-17 on Page 118– Write the problem, then the answer– Use the same paper as Transparency 13: Isotopes

and Mass Number

Mass of Atoms

• One atomic mass unit (amu) is defined as 1/12th the mass of a carbon-12 atom.

• One amu is nearly, but not exactly, equal to one proton and one neutron.

Mass of Atoms

• The atomic mass of an element is the weighted average mass of the isotopes of that element.

TITLE: Calculate the Atomic Mass of the Element “Snackium” (pg. 126)

OBJECTIVE: Observe the impact of the weights of different sub-atomic particles on the element; Infer the importance of each type of particle to the final weight of the element

PRE-LAB: First, read the entire Lab on Page 1261. What sub-atomic particles do the different types of snacks represent?2. The mass of neutrons and protons is much greater than the mass of electrons; therefore, the mass of an element is dominated by the mass of the nucleus. Predict which, if any, types of snacks will dominate the mass of your imaginary element.3. How will the mass of an isotope differ from the mass of the element?

DATA:Glue or paste the data table into your Lab Book

Math Skills Transparency 4: Calculating Atomic Mass

Mass of Atoms

• Practice Problems #18-19 on Page 121– Write the problem, then the answer

Homework, Section 3

• SECTION 3 REVIEW, Page 121• Questions #20-24• Answer with complete sentences• Due tomorrow

Section 4: Unstable Nuclei and Radioactive Decay

• National Standards:– B.2 Structure and properties of matter

Objectives – Section 4

• Explain the relationship between unstable nuclei and radioactive decay.

• Characterize alpha, beta, and gamma radiation in terms of mass and charge.

REVIEW VOCABULARY:• element: a pure substance that cannot be broken

down into simpler substances by physical or chemical means

New Vocabulary

• radioactivity alpha particle• radiation nuclear equation• nuclear reaction beta radiation• radioactive decay beta particle• alpha radiation gamma rays

• Unstable atoms emit radiation to gain stability.

Radioactivity

• Nuclear reactions can change one element into another element.

• In the late 1890s, scientists noticed some substances spontaneously emitted radiation, a process they called radioactivity.

• The rays and particles emitted are called radiation.

• A reaction that involves a change in an atom's nucleus is called a nuclear reaction.

Radioactivity

• Unstable nuclei lose energy by emitting radiation in a spontaneous process called radioactive decay.

• Unstable radioactive elements undergo radioactive decay thus forming stable nonradioactive elements.

Types of Radiation

• Alpha radiation is made up of positively charged particles called alpha particles.

• Each alpha particle contains two protons and two neutrons and has a 2+ charge.

Types of Radiation

• The figure shown below is a nuclear equation showing the radioactive decay of radium-226 to radon-222.

• An alpha particle is equivalent to a helium-4 nucleus and is represented by 4He or .

• Thus, showing mass is conserved in a nuclear equation.

Types of Radiation

• Beta radiation is radiation that has a negative charge and emits beta particles.

• Each beta particle is an electron with a 1– charge.

• During Beta decay, a neutron is converted to a proton and an electron. The electron is emitted and the proton stays in the nucleus.

Types of Radiation

Types of Radiation

• Gamma rays are high-energy radiation with no mass and are neutral.

• They usually accompany alpha and beta radiation.

• Gamma rays account for most of the energy lost during radioactive decay.

Types of Radiation

• Because gamma rays are massless, the emission of gamma rays by themselves cannot result in the formation of a new atom.

Types of Radiation

• Atoms that contain too many or two few neutrons are unstable and lose energy through radioactive decay to form a stable nucleus.

• Few exist in nature—most have already decayed to stable forms.

Transparency 14: Radioactive Particles

Questions: Mass Spectrometer – Chemical Detective

Homework, Section 4

• SECTION 4 REVIEW, Page 124 • Questions #25-29 – Answer with complete

sentences• Due tomorrow• Chapter 4 Test is tentatively scheduled for

Friday, October 11 . – Ch. 4 Vocab/Study Guide is due on Test Day.

Key Concepts

• Democritus was the first person to propose the existence of atoms.

• According to Democritus, atoms are solid, homogeneous, and indivisible.

• Aristotle did not believe in the existence of atoms.

• John Dalton’s atomic theory is based on numerous scientific experiments.

SECTION4.1

Early Ideas About Matter

Study Guide

Key Concepts

• An atom is the smallest particle of an element that maintains the properties of that element.

• Electrons have a 1– charge, protons have a 1+ charge, and neutrons have no charge.

• An atom consists mostly of empty space surrounding the nucleus.

SECTION4.2

Defining the Atom

Study Guide

Key Concepts

• The atomic number of an atom is given by its number of protons. The mass number of an atom is the sum of its neutrons and protons. atomic number = number of protons = number of electrons

mass number = atomic number + number of neutrons

• Atoms of the same element with different numbers of neutrons are called isotopes.

• The atomic mass of an element is a weighted average of the masses of all of its naturally occurring isotopes.

SECTION4.3

How Atoms Differ

Study Guide

Key Concepts

• Chemical reactions involve changes in the electrons surrounding the nucleus of an atom. Nuclear reactions involve changes in the nucleus of an atom.

• There are three types of radiation: alpha (charge of 2+), beta (charge of 1–), and gamma (no charge).

• The neutron-to-proton ratio of an atom’s nucleus determines its stability.

SECTION4.4

Unstable Nuclei and Radioactive Decay

Study Guide