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

Just how small is an atom

Unit 6 Lesson 6 The Atom 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). Period No. of students Passed Standard Percentage 1A 2/22 9% 2A 1/22 4% 4A 4/25 16% 1B 2/20 1% 3B 2/21 4B 1/21 Copyright © Houghton Mifflin Harcourt Publishing Company 3

Unit 6 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. . An element is a substance that cannot be separated or broken down into simpler substance. Copyright © Houghton Mifflin Harcourt Publishing Company 4

What is the atomic theory? Scientist Atom Model Description about the atomic theory John Dalton (1803) All substances are made of small particles, called atoms, that cannot be divided. J.J. Thomson (1897) Detected smaller particles within the atom. Believed these particles were mixed throughout the atom. Ernest Rutherford (1900s) Proposed atoms had a dense, positively charged nucleus surrounded by electrons.

Bohr’s Model of the atom

What are the parts of an atom? Unit 6 Lesson 6 The Atom What are the parts of an atom? Atoms are made of protons, neutrons, and electrons. 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. 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 7

What are the parts of an atom? Unit 6 Lesson 6 The Atom What are the parts of an atom? Neutrons are particles that have no electrical charge. The mass of a neutron is slightly more than a proton but is still considered to be 1 u. Electrons are negatively charged particles. Electrons move around the nucleus very quickly in a region called the electron cloud. The mass of an electron is 0 u. Copyright © Houghton Mifflin Harcourt Publishing Company 8

What are the parts of an atom? Unit 6 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 9

Take a Number! How can we describe atoms? Unit 6 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 10

How can we describe atoms? Unit 6 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 11

How can we describe atoms? Unit 6 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 12

How many electrons fit in each shell around an atom?

1st shell has 2 electrons 2nd shell has 8 electrons 3rd shell has 6 electrons Total= 16 electrons

Summary: What makes up an atom?