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Resources Chapter Presentation Bellringers Image Bank Standards Assessment Visual Concepts Math Focus

Introduction to Atoms Chapter 6 Table of Contents Section 1 Development of the Atomic Theory Section 2 The Atom

Section 1 Development of the Atomic Theory Chapter 6 Bellringer In your Science Journal, draw a picture that shows what you think an atom looks like. On your drawing, include labels for the locations of protons, neutrons, and electrons.

Section 1 Development of the Atomic Theory Chapter 6 What You Will Learn • There have been different models of the atom over time. • The atomic theory has changed as scientists have experimented and discovered new information about the atom.

Section 1 Development of the Atomic Theory Chapter 6 The Beginning of Atomic Theory • Matter is made of particles that we call atoms. • An atom is the smallest particle into which an element can be divided and still have the properties of that element.

Introduction to Atoms Chapter 6 Atom

Section 1 Development of the Atomic Theory Chapter 6 Dalton’s Atomic Theory Based on Experiments • By the late 1700s, scientists had learned that elements combine in certain proportions based on mass to form compounds. • Dalton’s atomic theory, published in 1803, suggested that elements combine in certain proportions because they are made of atoms.

Section 1 Development of the Atomic Theory Chapter 6 Thomson’s Discovery of Electrons • In 1897, Thomson’s experiments led him to conclude that there must be negatively charged particles inside the atom. These particles are now called electrons. • An electron is a subatomic particle that has a negative charge.

Introduction to Atoms Chapter 6

Section 1 Development of the Atomic Theory Chapter 6 Rutherford’s Atomic “Shooting Gallery” • In 1909, Rutherford designed an experiment to study the parts of an atom. • The results of Rutherford’s gold-foil experiment suggested that atoms are not all the same throughout. He concluded that atoms have different parts.

Section 1 Development of the Atomic Theory Chapter 6 The Nucleus and the Electrons • Rutherford’s results led him to conclude that most matter in an atom is found in one very small area. • In 1911, Rutherford revised the atomic theory and proposed that in the center of the atom is a tiny, extremely dense, positively charged area called the nucleus.

Section 1 Development of the Atomic Theory Chapter 6 The Nucleus and the Electrons, continued • In physical science, the nucleus is an atom’s central region which is made of protons and neutrons. • From Rutherford’s results, the important idea emerged that atoms are mostly empty space with a tiny, massive nucleus at the center and electrons surrounding the nucleus.

Section 1 Development of the Atomic Theory Chapter 6 The Nucleus and the Electrons, continued • In 1913, Bohr’s results led him to propose that electrons move around the nucleus in definite paths. • According to modern atomic theory, electrons are likely to be found moving in certain regions around the nucleus of an atom. These regions are called electron clouds, or orbitals.

Section 1 Development of the Atomic Theory Chapter 6 The Nucleus and the Electrons, continued • Electron clouds are regions around the nucleus of an atom where electrons are likely to be found. Each electron cloud has a definite energy level. • Therefore, each electron in an atom has a definite energy based on which electron cloud the electron is moving in.

Introduction to Atoms Chapter 6 Electron Cloud

Section 1 Development of the Atomic Theory Chapter 6 The Size of an Atom • Atoms are so small that light waves are too large to be used to observe them. Scientists use scanning tunneling electron microscopes to provide images of atoms. • However, these images are not an actual picture of the atom. They show an image of the surface of a material at the atomic level.

Section 2 The Atom Chapter 6 Bellringer An atom is the smallest particle of an element. Atoms are made of protons, neutrons, and electrons. Write a paragraph in your Science Journal explaining how the two sentences above relate to one another. Are they both true? If so, how is that possible?

Section 2 The Atom Chapter 6 What You Will Learn • Protons, neutrons, and electrons make up atoms. • All atoms of a given element have the same number of protons in the nucleus. • Isotopes of an element differ by the number of neutrons in the nucleus. • Atomic mass is an average of the masses of all of the naturally occurring isotopes of an element. • Four forces are at work in atoms.

Section 2 The Atom Chapter 6 The Parts of an Atom • Almost all kinds of atoms are made of the same three particles. These particles are protons, neutrons, and electrons. • Protons, neutrons, and electrons are called subatomic particles because they are each much smaller than an atom.

Section 2 The Atom Chapter 6 The Parts of an Atom, continued • The number of subatomic particles that are in an atom and the way the particles interact determine the properties of an atom. • A proton is a subatomic particle that has a positive charge and that is located in the nucleus of an atom.

Section 2 The Atom Chapter 6 The Parts of an Atom, continued • A neutron is a subatomic particle that has no charge and that is located in the nucleus of an atom. • An electron is a subatomic particle that has a negative charge and that is found outside the nucleus in electron clouds.

Section 2 The Atom Chapter 6 The Parts of an Atom, continued • The charges of protons and electrons are opposite but equal, so the charges cancel out. If the numbers of electrons and protons become unequal, the atom becomes a charged particle called an ion. • The SI unit that is used to express the mass of a particle in an atom is the atomic mass unit (amu).

Section 2 The Atom Chapter 6 Atoms and Elements • There are more than 110 different elements. The atoms of each of these elements are different from the atoms of all other elements. • Electrons and protons are found in all atoms. • An atom does not have to have equal numbers of neutrons and protons.

Section 2 The Atom Chapter 6 Atoms and Elements, continued • The atomic number is the number of protons in the nucleus of an atom. • All atoms of the same element have the same atomic number. • The atomic number of each element is listed on the periodic table.

Introduction to Atoms Chapter 6 Atomic Number

Section 2 The Atom Chapter 6 Isotopes • An isotope is an atom that has the same number of protons as other atoms of the same element do, but has a different number of neutrons. • Atoms that are isotopes of each other are always the same element, because isotopes of the same element always have the same number of protons.

Section 2 The Atom Chapter 6 Isotopes, continued • Some isotopes of an element have special properties because they are unstable. An unstable atom is an atom with a nucleus that will change over time. This type of atom is radioactive. • Isotopes of an element share most of the same chemical and physical properties.

Section 2 The Atom Chapter 6 Isotopes, continued • Each isotope of an element can be identified by its mass number. The mass number is the sum of the protons and neutrons in the nucleus of an atom. • To identify a specific isotope of an element, write the name of the element followed by a hyphen and the mass number of the isotope.

Introduction to Atoms Chapter 6 Mass Number

Section 2 The Atom Chapter 6 Isotopes, continued • Most elements contain a mixture of two or more isotopes. • The atomic mass of an element is the weighted average of the masses of all the naturally occurring isotopes of that element.

Section 2 The Atom Chapter 6 Forces in Atoms • There are four basic forces that are at work everywhere in nature, even within the atom. These forces are gravitational force, electromagnetic force, strong force, and weak force. • These four forces work together to give an atom its structure and properties.

Introduction to Atoms Chapter 6 Concept Map Use the terms below to complete the concept map on the next slide.

Introduction to Atoms Chapter 6 Concept Map

Introduction to Atoms Chapter 6 End of Chapter 6 Show

Standards Assessment Chapter 6 1. Which of the following words is the closest in meaning to the word distinct? A. separate B. similar C. approximate D. varying

Standards Assessment Chapter 6 2. In the sentence “The structure of a substance is determined by its atoms,” what does the word structure mean? A. destruction B. resistance C. composition D. elements

Standards Assessment Chapter 6 3. Which of the following words best completes the following sentence: “An element has a _____ number of protons in its nucleus”? A. large B. specific C. differing D. negative

Standards Assessment Chapter 6 4. Which of the following words is closest in meaning to the word investigation? A. plan B. inquiry C. gathering D. development

Standards Assessment Chapter 6 5. All matter is made up of atoms. Which sentence correctly describes atoms? A. All substances are made of the same atoms. B. Atoms are the smallest particle of a nucleus. C. An atom is the smallest particle of an element. D. An atom is a substance that has been cut in half.

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