Chem chapt 4

Chemistry Chapter 4 Structure of the Atom

Main Ideas The ancient Greeks tried to explain matter, but the scientific study of the atom began with John Dalton in the early 1800's. An atom is made of a nucleus containing protons and neutrons; electrons move around the nucleus. The number of protons and the mass number define the type of atom. Unstable atoms emit radiation to gain stability.

Early Ideas about Matter Objectives: Compare and contrast the atomic models of Democritus, Aristotle, and Dalton. Understand how Dalton's theory explains the conservation of mass.

Greek Philosophers 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.

Democritus 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.

Aristotle 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.

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 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.

Dalton’s Atomic Theory Even though some of the theory was incorrect, It provided the basis we have today for atomic theory. As is common with science, his theory has since been revised and additional information learned.

Dalton’s Atomic Theory Which parts of Dalton’s Atomic Theory was incorrect? Atoms are indivisible. Atoms of a given element are identical in size, mass and chemical properties.

Question ? Who was the first person to propose the idea that matter was not infinitely divisible? A. Aristotle B. Plato C. Dalton D. Democritus

Question? Dalton’s theory also conveniently explained what? A. the electron B. the nucleus C. law of conservation of mass D. law of Democritus

Defining the Atom Objectives 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.

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. Gerd Binnig and Heinrich Rohrer won the Nobel Prize in 1986 for the invention of the STM

STM Scanning tunneling microscopy (STM) is the highest resolution imaging and nanofabrication technique available. It relies on quantum tunneling of electrons from a sharp metal tip to a conducting surface. The 71 Angstrom diameter "quantum corral" shown above was created and imaged with an ultra-high vacuum cryogenic STM. Each sharp peak in the circle is an iron atom resting on atomically flat copper

Cathode Ray Tube 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 .

Cathode Ray Tube Thomson received the Nobel Prize in 1906 for identifying the first subatomic particle—the electron. Research with the Cathode Ray Tube determined the following: Cathode rays were a stream of charged particles The particles carried a negative charge. Changing the metal that made up the electrodes did not change the ray, therefore all types of matter had these particles.

Milikan’s Oil Drop Experiment 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

Early Atomic Models Matter is neutral. J.J. Thomson's plum pudding model of the atom states that the atom is a uniform, positively changed 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 The repulsive force between the positively charged nucleus and positive alpha particles caused the deflections.

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 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.

The Nucleus All atoms are made of three fundamental subatomic particles: the electron, the proton, and the neutron. Atoms are spherically shaped.

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

Question? Atoms are mostly ____. A. positive B. negative C. solid spheres D. empty space

Question? What are the two fundamental subatomic particles found in the nucleus? A. proton and electron B. proton and neutron C. neutron and electron D. neutron and positron

How Atoms Differ Objectives: 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.

Atomic Number Moseley (1887-1915) discovered 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 .

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 The relative abundance of each isotope is usually constant. Isotopes containing more neutrons have a greater mass. Isotopes have the same chemical behavior. The mass number is the sum of the protons and neutrons in the nucleus.

Mass of Atoms One atomic mass unit (amu) is defined as 1/12 th 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.

Question? An unknown element has 19 protons, 19 electrons, and 3 isotopes with 20, 21 and 22 neutrons. What is the element’s atomic number? A. 38 B. 40 C. 19 D. unable to determine

Question ? Elements with the same number of protons and differing numbers of neutrons are known as what? A. isotopes B. radioactive C. abundant D. ions

Unstable Nuclei and Radioactive Decay Objective: Explain the relationship between unstable nuclei and radioactive decay. Characterize alpha, beta, and gamma radiation in terms of mass and charge.

Radioactivity 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 . Nuclear reactions can change one element into another element.

Radioactive Decay 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. Nuclear stability is determined by the ratio of neutrons to protons.

Radioactive Decay Atoms that contain too many or too 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.

Alpha Particle 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. Found because they are deflected towards a negavtively charged plate.

Alpha Particle The figure shown below is a nuclear equation showing the radioactive decay of radium-226 to radon-222. The mass is conserved in nuclear equations.

Beta Particle Beta radiation is radiation that has a negative charge and emits beta particles. Each beta particle is an electron with a 1– charge. Found because they are deflected toward the positive charged plate

Gamma Rays Gamma rays are high-energy radiation with no mass and are neutral and cannot, by themselves, result in the formation of a new atom. Gamma rays account for most of the energy lost during radioactive decay.

Question ? A reaction that changes one element into another is called what? A. chemical reaction B. beta radiation C. nuclear reaction D. physical reaction

Question ? Why are radioactive elements rare in nature? A. They do no occur on Earth. B. Most have already decayed to a stable form. C. They take a long time to form. D. They are too hard to detect.

Study Guide 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.

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.

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.

Study Guide Key Concepts Chemical reactions involve changes in the electrons surrounding 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.

Question? Whose work led to the modern atomic theory? A. Dalton B. Rutherford C. Einstein D. Aristotle

Question? Which particle is not found in the nucleus of an atom? A. neutron B. proton C. dust D. electron

Question? Two isotopes of an unknown element have the same number of: A. protons B. neutrons C. electrons D. both A and C

Question? Lithium has an atomic mass of 6.941 and two isotopes, one with 6 neutrons and one with 7 neutrons. Which isotope is more abundant? A. 6 Li B. 7 Li C. Both isotopes occur equally. D. unable to determine

Question? What happens when an element emits radioactive particles? A. It gains energy. B. It gains neutrons. C. It loses stability. D. It loses energy.

Question? What is the smallest particle of an element that still retains the properties of that element? A. proton B. atom C. electron D. neutron

Question? How many neutrons, protons, and electrons does 124 54 Xe have? A. 124 neutrons, 54 protons, 54 electrons B. 70 neutrons, 54 protons, 54 electrons C. 124 neutrons, 70 protons, 54 electrons D. 70 neutrons, 70 protons, 54 electrons

Question? The primary factor in determining an atom's stability is its ratio of neutrons to ____. A. protons B. electrons C. alpha particles D. isotopes

Question? What is the densest region of an atom? A. electron cloud B. nucleus C. isotopes D. atomic mass

Question? Why are electrons attracted to the cathode in a cathode ray tube? A. The cathode is more stable. B. The cathode has a positive charge. C. The cathode has a negative charge. D. The cathode has no charge.

CIM Table 4.3 Properties of Subatomic Particles Figure 4.12 Rutherford's Experiment Figure 4.14 Features of an Atom Figure 4.21 Types of Radiation

Help Click any of the background top tabs to display the respective folder. Within the Chapter Outline, clicking a section tab on the right side of the screen will bring you to the first slide in each respective section. Simple navigation buttons will allow you to progress to the next slide or the previous slide. The “Return” button will allow you to return to the slide that you were viewing when you clicked either the Resources or Help tab. The Chapter Resources Menu will allow you to access chapter specific resources from the Chapter Menu or any Chapter Outline slide. From within any feature, click the Resources tab to return to this slide. To exit the presentation, click the Exit button on the Chapter Menu slide or hit Escape [Esc] on your keyboards while viewing any Chapter Outline slide.

End of Custom Shows This slide is intentionally blank.

Chem chapt 4

More Related Content

What's hot (19)

Viewers also liked (20)

Similar to Chem chapt 4 (20)

More from bobcatchemistry (20)

Recently uploaded (20)

Chem chapt 4