How Is the Structure of the Atom Related to Its Behavior?

How is the structure of the atom related to its behavior?

Chemistry: Unit 3

New Skills:

c Calculate weighted atomic masses

c Predict products of a nuclear reaction

c Calculate Half-life

Academic Language:

Dalton’s Atomic Theory
Atom
Cathode ray
Electron
Neutron
Nucleus
Proton
Atomic mass
Atomic number
Isotope
Mass number
Alpha particle
Alpha radiation
Beta particle
Beta radiation
Gamma ray
Nuclear equation
Nuclear Reaction
Radioactivity
Radiation
Radioactive decay

Unit 3 Homework:

CALM: http://calm.indiana.edu/

3:1 Early Ideas about Matter:

c 10 questions

3:2 Defining the Atom:

c 10 questions

3:3 How Atoms Differ:

c 10 questions

3:4 Unstable Nuclei and Radioactive Decay:

c 10 questions

3:5 Accumulating Content and Skills:

c 10 questions

Chemistry Unit 3: Learning Goals and Objectives

3:1 Early Ideas about Matter - The ancient Greeks tried to explain matter, but the scientific study of the atom began with John Dalton in the early 1800’s.

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

· Understand how Dalton’s theory explains the conservation of mass.

3:2 Defining the Atom – An atom is made of a nucleus containing protons and neutrons; electrons move around the nucleus.

· 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.

3:3 How Atoms Differ – The number of protons and the mass number define the type of atom.

· 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.

3:4 Unstable Nuclei and Radioactive Decay – Unstable atoms emit radiation to gain stability.

· Explain the relationship between unstable nuclei and radioactive decay.

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

· Solve problems involving radioactive decay rates.

3:5 – Accumulating Content and Skills:– Chemistry content is continuous and builds on prior knowledge and skills. This section will combine this unit with previous units.

· Apply knowledge and skills from previous units to content learned in this unit.

3:1 Early ideas about Matter- The ancient Greeks tried to explain matter, but the scientific study of the atom began with John Dalton in the early 1800’s.

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

Early Greek Philosophers - Many concluded that matter was composed of things such as earth, water, air and fire

Democritus- (Greek 460-370BC)- the first to propose the idea that matter was not infinitely divisible. He believed matter was made up of tiny individual particles called atomos. He felt that these atoms could not be created nor destroyed or further divided.

Aristotle- (Greek 384-322BC) - One of the most influential philosophers of his time. He disagreed with Democritus , one reason being he didn’t believe that empty space existed. Aristotle’s views went unchallenged for 2000 years until science developed methods to test the validity of his ideas.

**It was difficult for Democritus to defend his ideas because controlled experiments on his theory were not possible.**

Objective: Understand how Dalton’s theory explains the conservation of mass.

John Dalton – (English school teacher -1766-1844) – Responsible for the beginning of the development of modern atomic theory. Dalton revised Democritus’s theories by performing and studying many chemical reactions. Through careful observations and measurements he was able to determine mass ratios of the elements involved in those reactions.

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

Dalton’s Atomic Theory

John Dalton’s theory, proposed in 1803 is known as Dalton’s atomic theory.

1. Matter is composed of extremely small particles called atoms.

2. Atoms are indivisible and indestructible

3. Atoms of a given element are identical in size, mass, and chemical properties.

4. Atoms of a specific element are different from those of another element.

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

6. In a chemical ration, atoms are separated, combined or rearranged.

***Even though some of the theory was incorrect, it provided the basis we have today for atomic theory. As with science, his theory has since been revised and additional information learned.***

Which parts of Dalton’s Atomic Theory were incorrect?

Why?

3:2 Defining the Atoms - An atom is made of a nucleus containing protons and neutrons; electrons move around the nucleus.

Objective: Define atom

Atoms – the smallest particle of an element that retains the properties of that element.

Objective: Distinguish between the subatomic particles in terms of relative charge and mass

Objective: Describe the structure of the atom, including the locations of the subatomic particles.

Cathode- Ray Tube – Glass tube from which most of the air has been removed and electricity is passed through it. The ray originating from the cathode end (negative) to the anode (positive) is called a cathode ray.

Electrons – The negative charged particles that are part of all forms of matter.

Thomson by measuring the effects of magnetic and electric fields on a cathode ray, a charge to mass ratio was determined. It was determined that the mass of the charged particle was much smaller than a H atom so therefore there is something smaller than an atom. He won the Nobel Prize in 1906 for identifying first subatomic particle.

Research of the cathode ray determined the following:

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

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

Mass of an electron - 9.1 x 10-28 or 1/1840 the mass of H

Early Models Atomic Models–

• Plum Pudding Model by Thomson – states that the atom is a uniform, positively changed sphere containing electrons.

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

Rutherford’s experiment and model – the firing of alpha particles through a thin gold foil, found that alpha particles were deflected at many angles and most pass right through. Therefore most of the atom was space with a dense center.

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

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

Nucleus- The dense center region of the atom that is positively charged.

· 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.

Niels Bohr- 1913 atomic structure relating to electron arrangement.

The Nucleus

· Proton – a subatomic particle carrying an equal but opposite charge of an electron. By 1920, Rutherford had refined his concept and concluded that the positively charge particles in the nucleus were protons.

· Neutron – subatomic particle that has a mass nearly equal to a proton but carries no electric charge. Chadwick – Rutherford’s coworker received Nobel in 1935 for this discovery.

The Nucleus

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

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

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

3:3 How Atoms Differ -The number of protons and the mass number define the type of atom.

Objective: Explain the role of atomic number in determining the identity of an atom

Atomic number – the number of protons in the nucleus of an atom identifies the element.

· Moseley (1887-1915) discovered …..

Objective: Define an isotope

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

· Isotopes – Atoms with the same number of protons and electrons but different numbers of neutrons.

· Isotopes have the same chemical behavior.

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

Examples of notation:

Objective: Explain why atomic masses are not whole numbers

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

AMU – atomic mass unit – based on carbon-12 atom – therefore amu is defined as 1/12th the mass of carbon.

Atomic Mass – is a weighted average of the mass of the isotopes of that element and therefore is not a whole number.

Example Problem: Silver has two isoptopes: , which has a mass of 106.905 amu and a percent abundance of 52.00%, and , which has a mass of 108.905 amu and a percent abundance of 48.00%. What is the atomic mass of silver?

Example Problem 2: Chromium’s four naturally occurring isotopes are provided. Calculate chromium’s atomic mass.

Cr-50 4.35% 49.946amu

Cr-52 83.79% 51.941amu

Cr-53 9.50% 52.941amu

Cr-54 2.36% 53.939amu

3:4 Unstable Nuclei and Radioactive Decay - Unstable atoms emit radiation to gain stability.

Objective: Explain the relationship between unstable nuclei and radioactive decay

Radioactivity – is the spontaneous emission of radiation by a radioactive material

· Radiation – is the rays and particles emitted during a nuclear reaction.

· Nuclear Reaction – can change an element into a new element by changing an atom’s nucleus.

Radioactive decay – is a spontaneous process by which unstable nuclei lose energy by emitting radiation.

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

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

Transmutation- When a reaction occurs that alters an atom’s atomic number.

· Positron –

· Electron Capture -

Types of Radiation:

Alpha radiation – is made up of positively charged particles called alpha particles

· Found because they are deflected towards a negavtively charged plate.

o or α

Example equation: nuclear equation showing the radioactive decay of radium-226 to radon-222.

Beta Radiation – is radiation that has a negative charge and emits beta particles

· Found because they are deflected toward the positive charged plate

o β or e-

o Example equation:

Gamma radiation – a high energy radiation that possesses no mass and no charge.

o Cannot, by themselves, result in the formation of a new atom.

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

o γ

o Example equation:

Objective: Solve problems involving radioactive decay rates.

Radiochemical Dating: Carbon undergoes beta decay to form nitrogen. Carbon-14 has a half-life of 5730 years.

· The amount of stable carbon in the dead organism remains constant while the carbon-14 continues to decay, the ratio of unstable carbon-14 to stable carbon-12 and 13 decreases over time.

Half-life – is the time required for one-half of a radioisotope’s nuclei to decay into its products.

· N is the remaining amount

· No is the initial amount

· n is the number of half-lives that have passed. (or this can be replaced with t/T where t is the elapsed tie and T is the duration of the half-life with the same units in time).

Example Problem: Krypton-85 is used in indicator lights of appliances. The half-life of krypton-85 is 11years. How much of a 2.00 mg sample remains after 33 years?

Example Problem 2: Bandages can be sterilized by exposure to gamma radiation from cobalt-60, which has a half-life of 5.27 years. How much of a 10.0mg sample of cobalt-60 is left after one half life? Two half lives? Three half lives?

3:5 – Accumulating Content and Skills:– Chemistry content is continuous and builds on prior knowledge and skills. This section will combine this unit with previous units.

Objective: Apply knowledge and skills from previous units to content learned in this unit.

· How does law of conservation of mass apply to nuclear reactions?

· How did the scientific method affect the history of chemistry?