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6-2 Notes: The Atom Almost all kinds of atoms are made of the same three particles. These particles are protons, neutrons, and electrons. They are known as subatomic particles because they are much smaller than an atom. The number of subatomic particles in an atom and the way they interact determine the properties of the atom. Protons are positively charged particles of the nucleus. The SI unit that describes the mass of a particle in an atom is the atomic mass unit (amu). Each proton has a mass of about 1 amu. Neutrons are the particles of the nucleus that have no electric charge. The mass of a neutron can be thought of as 1 amu. Protons and neutrons are the most massive particles in an atom. The volume of the nucleus is very small. So, the nucleus is very dense. Electrons are the negatively charged particles in atoms. They are found outside the nucleus in electron clouds. It takes more than 1,800 electrons to equal the mass of 1 proton. The mass of an electron is so small that it is usually thought of as almost zero. The charges or 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. An atom that loses one or more electrons becomes a positively charged ion. An atom that gains one or more electrons becomes a negatively charged ion. There are more than 110 different elements. The atoms of each element are different from atoms of all other elements. The number of protons in the nucleus of an atom is the atomic number of that atom. All atoms of the same element have the same atomic number. Isotopes are atoms that have the same number of protons but have different numbers of neutrons. Atoms that are isotopes of each other are always the same element, because isotopes have the same number of protons. They have different numbers of neutrons, however, which gives them different masses. An unstable atom is an atom with a nucleus that will change over time. This type of isotope is radioactive. Radioactive atoms spontaneously fall apart after a certain amount of time, giving off smaller particles and energy. Isotopes of an element share most of the same chemical and physical properties. The mass number is the sum of the protons and neutrons in an atom. You can calculate the number of neutrons in an atom by subtracting the atomic number from the mass number. The atomic mass of an element is the weighted average of the masses of all the naturally occurring isotopes of that element. Unit 3 (Ch.6) – Atom/Periodic Table Bach 10//05/09 The forces at work in atom are gravitational force, strong force, electromagnetic force, and weak force. Section 6-2 Review 1. What are the three subatomic particles that make up an atom? Protons, neutrons, and electrons. 2. List the charge and location for each subatomic particle. Protons: + charge, nucleus Neutrons: 0 charge, nucleus Electrons: - charge, electron cloud 3. Describe an atom that has 8 protons, 8 neutrons, and 10 electrons. An atom with 8 protons would be an oxygen atom, but with 10 electrons it would be a negative ion with an overall charge of -2. 4. What is an atom’s atomic number equal to? The number of protons in the nucleus of the atom. 5. How do isotopes of the same element differ from one another? Isotopes of the same element differ from one another in the number of neutrons in the nucleus of the atom. 6. How can you determine the mass number of an atom? The mass number is the sum of the protons and neutrons in the nucleus of an atom. 7. How many neutrons are in an atom that has a mass number of 51 and an atomic number of 23? Subtracting the number of protons (atomic number) from the mass number gives the number of neutrons in the nucleus of an atom: 28. 8. What are the four forces at work in an atom? The forces at work in atom are gravitational force, strong force, electromagnetic force, and weak force. Unit 3 (Ch.6) – Atom/Periodic Table Bach 10//05/09 6-2 Notes: The Atom Almost all kinds of atoms are made of the same _______ particles. These particles are protons, _________, and electrons. They are known as____________ particles because they are much smaller than an atom. The number of subatomic particles in an atom and the way they interact determine the _____________ of the atom. __________ are positively charged particles of the nucleus. The SI unit that describes the mass of a particle in an atom is the ________ ______ unit (amu). Each proton has a mass of about _______. __________ are the particles of the nucleus that have no electric charge. The _______ of a neutron can be thought of as 1 amu. Protons and neutrons are the most __________ particles in an atom. The ___________ of the nucleus is very small. So, the nucleus is very ___________. ____________ are the negatively charged particles in atoms. They are found outside the nucleus in electron __________. It takes more than ________ electrons to equal the mass of 1 proton. The mass of an electron is so small that it is usually thought of as almost _________. The charges or protons and electrons are opposite but _________, so the charges cancel out. If the numbers of electrons and protons become unequal, the atom becomes a charged particle called an ______. An atom that loses one or more electrons becomes a _______________ charged ion. An atom that gains one or more electrons becomes a ______________ charged ion. There are more than 110 different _____________. The atoms of each element are _____________ from atoms of all other elements. The number of protons in the nucleus of an atom is the _________ __________ of that atom. All atoms of the same ____________ have the same atomic number. Isotopes are atoms that have the same number of protons but have different numbers of ___________. Atoms that are ____________ of each other are always the same element, because isotopes have the same number of protons. They have different numbers of neutrons, however, which gives them different ___________. An unstable atom is an atom with a ___________ that will change over time. This type of isotope is _______________. Radioactive ______ spontaneously fall apart after a certain amount of time, giving off smaller particles and energy. Isotopes of an element ________ most of the same chemical and physical properties. The ______ __________ is the sum of the protons and neutrons in an atom. You can calculate the number of ___________ in an atom by subtracting the atomic number from the mass number. The atomic mass of an element is the weighted average of the __________ of all the naturally occurring isotopes of that element. Unit 3 (Ch.6) – Atom/Periodic Table Bach 10//05/09 The forces at work in atom are gravitational force, __________ force, electromagnetic force, and weak force. Section 6-2 Review 1. What are the three subatomic particles that make up an atom? 2. List the charge and location for each subatomic particle. 3. Describe an atom that has 8 protons, 8 neutrons, and 10 electrons. 4. What is an atom’s atomic number equal to? 5. How do isotopes of the same element differ from one another? 6. How can you determine the mass number of an atom? 7. How many neutrons are in an atom that has a mass number of 51 and an atomic number of 23? 8. What are the four forces at work in an atom? Unit 3 (Ch.6) – Atom/Periodic Table Bach 10//05/09