Unit 2 Lesson 6 The Atom Copyright © Houghton Mifflin Harcourt Publishing Company 1

Unit 2 Lesson 6 The Atom Florida Benchmarks SC.8.P.8.7 Explore the scientific theory of atoms (also known as atomic theory) by recognizing that atoms are the smallest unit of an element and are composed of subatomic particles (electrons surrounding a nucleus containing protons and neutrons). LA.6.2.2.3 The student will organize information to show understanding (e.g., representing main ideas within text through charting, mapping, paraphrasing, summarizing, or comparing/contrasting). Copyright © Houghton Mifflin Harcourt Publishing Company 2

As a Matter of Fact … What is matter made of? Unit 2 Lesson 6 The Atom As a Matter of Fact … What is matter made of? The Greek philosopher Democritus thought matter could be divided into smaller and smaller units he called atomos. In 1803, John Dalton proposed that all substances are made of atoms that cannot be divided. Copyright © Houghton Mifflin Harcourt Publishing Company 3

Unit 2 Lesson 6 The Atom What is matter made of? In 1897, J. J. Thomson performed experiments that detected smaller particles within atoms. In the early 1900s, Ernest Rutherford and James Chadwick revealed the nature of the dense center of an atom. Today we have the electron cloud model. Copyright © Houghton Mifflin Harcourt Publishing Company 4

Unit 2 Lesson 6 The Atom What are atoms? An atom is the smallest particle into which an element can be divided and still be the same substance. In 1808, John Dalton published an atomic theory that said all atoms of a particular element are identical. Dalton also said that atoms of an element differ from atoms of other elements. Copyright © Houghton Mifflin Harcourt Publishing Company 5

Up and Atom! What are the parts of an atom? Unit 2 Lesson 6 The Atom Up and Atom! What are the parts of an atom? Atoms are made of protons, neutrons, and electrons. Protons are positively charged particles. The mass of a proton is given in the atomic mass unit (u). One proton has a mass of 1 u. Copyright © Houghton Mifflin Harcourt Publishing Company 6

What are the parts of an atom? Unit 2 Lesson 6 The Atom What are the parts of an atom? Neutrons are particles that have no electrical charge. In most atoms, there are at least as many neutrons as protons. The mass of a neutron is slightly more than a proton but is still considered to be 1 u. Copyright © Houghton Mifflin Harcourt Publishing Company 7

What are the parts of an atom? Unit 2 Lesson 6 The Atom What are the parts of an atom? The nucleus is the at the center of the atom and contains the protons and neutrons. The overall charge of the nucleus is equal to the number of protons in the nucleus. The nucleus is small but very dense. Copyright © Houghton Mifflin Harcourt Publishing Company 8

What are the parts of an atom? Unit 2 Lesson 6 The Atom What are the parts of an atom? Electrons are negatively charged particles. Electrons move around the nucleus very quickly in a region called the electron cloud. Electrons are very small compared to protons and neutrons. Copyright © Houghton Mifflin Harcourt Publishing Company 9

What are the parts of an atom? Unit 2 Lesson 6 The Atom What are the parts of an atom? Why is the exact location of an electron are hard to identify? Copyright © Houghton Mifflin Harcourt Publishing Company 10

What are the parts of an atom? Unit 2 Lesson 6 The Atom What are the parts of an atom? The number of protons and electrons in an atom are the same, so the charges are balanced. An atom can gain or lose electrons to become an ion, which has a net positive or negative charge. Copyright © Houghton Mifflin Harcourt Publishing Company 11

Take a Number! How can we describe atoms? Unit 2 Lesson 6 The Atom Take a Number! How can we describe atoms? Different combinations of protons, neutrons, and electrons produce atoms with different properties. The number of each kind of particle within an atom determines its unique properties. Copyright © Houghton Mifflin Harcourt Publishing Company 12

How can we describe atoms? Unit 2 Lesson 6 The Atom How can we describe atoms? The number of protons distinguishes the atoms of one element from the atoms of another. The number of protons in the nucleus of an atom is the atomic number of that atom. Copyright © Houghton Mifflin Harcourt Publishing Company 13

How can we describe atoms? Unit 2 Lesson 6 The Atom How can we describe atoms? Atoms of an element have the same number of protons, but the number of neutron may differ. Isotopes are atoms of the same element that have different numbers of neutrons. The total number of protons and neutrons in an atom’s nucleus is its mass number. Copyright © Houghton Mifflin Harcourt Publishing Company 14