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Unit 2 Lesson 6 The Atom Copyright © Houghton Mifflin Harcourt Publishing Company 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 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 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 Unit 2 Lesson 6 The 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. • Help make up the nucleus of the atom • Help identify the atom (could be considered an atom’s DNA) + +++ + + + + • Equal to the atomic number of the atom • Equal to the number of electrons + Copyright © Houghton Mifflin Harcourt Publishing Company 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 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 Unit 2 Lesson 6 The 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. • Found outside the nucleus of the atom, in the electron orbits/levels; each orbit/level can hold a maximum number of electrons ( 1st = 2, 2nd = 8, 3rd = 8 or 18, etc…) • Move so rapidly around the nucleus that they create an electron cloud • Equal to the number of protons • Involved in the formation of chemical bonds + +++ ++++ - - Copyright © Houghton Mifflin Harcourt Publishing Company - Unit 2 Lesson 6 The Atom Copyright © Houghton Mifflin Harcourt Publishing Company Unit 2 Lesson 6 The Atom What are the parts of an atom? Copyright © Houghton Mifflin Harcourt Publishing Company Unit 2 Lesson 6 The Atom Copyright © Houghton Mifflin Harcourt Publishing Company Hydrogen (H) Atom Notice the one electron in the first orbital + =1 - =0 - =1 + Even though there are no neutrons present, Hydrogen is still considered an atom How many more electrons can fit in the 1st orbital/ level? Oxygen (O) Atom Notice the two electrons in the first orbital/level and the six in the second + =8 - =8 - - - =8 ++ + + + + + + - - - - How many more electrons can fit in the 2nd orbital/ level? Sodium (Na) Atom Notice the two electrons in the first orbital/level, eight in the second, and one in the third - + = 11 - - - = 12 - = 11 ++ + + + + + + - - - - - How many more electrons can fit in the 3rd orbital/ level? 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 Unit 2 Lesson 6 The Atom • An atom that carries an electrical charge is called an ion • If the atom loses electrons, the atom becomes positively charged (because the number of positively charged protons will be more the number of electrons) • If the atom gains electrons, the atom becomes negatively charged (because there are more negative charges than positive) Copyright © Houghton Mifflin Harcourt Publishing Company Unit 2 Lesson 6 The Atom The number of protons does not change in an ion. The number of neutrons does not change in an ion. So, both the atomic number and the atomic mass remain the same. This atom has lost an electron. Now it has one more proton than electron. One more proton means one more positive charge. This makes the total charge of the atom POSITIVE. Cation = positively charged particle This atom has gained an electron. Now it has one less proton than electron. One less proton means one less positive charge. This makes the total charge of the atom NEGATIVE. Anion = negatively charged particle Copyright © Houghton Mifflin Harcourt Publishing Company 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 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 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 Unit 2 Lesson 6 The Atom Describing Atoms • Atomic Number = number of protons • In a neutral atom, the # of protons = the # of electrons • Atomic Mass= the number of protons + the number of neutrons Copyright © Houghton Mifflin Harcourt Publishing Company Mass Number The total number of protons and neutrons in an atom’s nucleus Expressed in Atomic Mass Units (amu) Each proton or neutron has a mass of 1 amu What would be the mass number of this atom? + - 3 4 + ++ 3 protons + 4 neutrons = a mass number of 7 amu Why did we not account for the electrons when calculating the mass number? - - Building Atoms Using the whiteboard and the proton, neutron, and electron pieces, build the following atoms, and determine their atomic and mass numbers. Atoms Carbon Beryllium Oxygen Lithium Sodium Protons 6 4 8 3 11 Neutrons Electrons 6 6 5 4 8 8 4 3 12 11 Unit 2 Lesson 6 The Atom Isotopes The number of protons for a given atom never changes. The number of neutrons can change. Two atoms with different numbers of neutrons are called isotopes Isotopes have the same atomic # Isotopes have different atomic Mass #’s Copyright © Houghton Mifflin Harcourt Publishing Company Unit 2 Lesson 6 The Atom Copyright © Houghton Mifflin Harcourt Publishing Company