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Isotopes and the Mass of an Atom Unit 1, Part 2 Ch. 2 & 4 Coral Gables Senior High Ms. Kiely Pre-IB Chemistry I Bell-Ringer #1 How are the atoms of one element different from the atoms of another element? Back to Part 1 Slides Review: I. II. The atom is made up of three subatomic particles: the proton, the neutron, and the electron. Protons and neutrons (nucleons) are located in the center of an atom; a region called the nucleus. Electrons are found very far from the nucleus, surrounding the nucleus in what we call the electron cloud. III. Protons and neutrons are further broken down into quarks. Electrons, however, are fundamental particles; they cannot be further broken down/are not made up of smaller particles. Review: IV. The atomic number, number of protons in the nucleus, differentiates the atoms of one element from the atoms of other elements. V. The state that matter is in depends on the kinetic energy of its particles Element: an element is anything that consists of one type of atom. *Molecule: the term molecule is often misused. The term “molecule” is also used to describe atoms that are bonded together; however, it is only used when the bonded atoms are nonmetal atoms! Also, the nonmetal atoms that are bonded together can be of the same element or be of different elements. Compound: a substance made by chemically combining two or more elements. It has different properties from its constituent elements. Matter is either pure or mixed. Pure matter is anything that is made up of only one type of atom (an element), or one type of compound. Mixed matter is anything that is made up of different elements and compounds that are not chemically bonded together. John Dalton John Dalton was an English chemist who, similar to Democritus, proposed that all matter was made up of small, indivisible spheres called atoms. Unlike Democritus, though, Dalton actually had empirical reasoning for this; he performed many experiments with gases, which led him to his conclusions. Dalton’s Atomic Theory: ● All matter is composed of tiny indivisible particles called atoms ● Atoms cannot be created or destroyed ● Atoms of different elements are different ● Atoms can combine together in small numbers to form molecules and compounds ● Atoms of the same element are alike in every way Was Dalton Right? True or False: “All matter is composed of tiny indivisible particles called atoms” False! The atom is NOT fundamental. It is made up of protons, neutrons and electrons, and therefore is divisible. Was Dalton Right? True or False: “Atoms cannot be created or destroyed” True! The Law of Conservation of Mass states that mass can neither be created nor destroyed. Mass is of course referring to atoms. Atoms are not destroyed and created during chemical reactions; they are only rearranged. Was Dalton Right? True or False: “Atoms of different elements are different” True! The atomic number, (number of protons in the nucleus), differentiates the atoms of one element from another. Was Dalton Right? True or False: “Atoms can combine together in small numbers to form molecules and compounds” True! Atoms chemically combine together in whole-number ratios to form compounds and molecules. i.e. H₂O and CO₂ Was Dalton Right? True or False: “Atoms of the same element are alike in every way” False! Even though every atom of one element has the same atomic number, (the same number of protons in its nucleus), they do not necessarily have to have the same number of neutrons! Isotope: isotopes are atoms that have the same number of protons but different numbers of neutrons. Each of these nuclei represent hydrogen because they each only have 1 proton; however, they are not alike in every way since they each have different amounts of neutrons. 1. Carbon has many isotopes. If you find an isotope of carbon that has a mass number of 13, how many neutrons does the atom have? 2. Why are O-16, O-17, and O-18 examples of isotopes? 3. How many protons and neutrons do O-16, O-17, and O-18 have, respectively? Mass Numbers Since we know that isotopes exist, we know that not all atoms of an element are identical. All the atoms of an element will have the same number of protons, but not necessarily the same number of neutrons. This means that some atoms of an element have more mass than others! We determine the mass of an atom by taking a look at its nucleus. Mass Number = # of protons + # of neutrons Electrons are SO SMALL that they are not considered when determining the mass of an atom. Mass Numbers Practice: 1) What is the mass of an Oxygen atom that contains 9 neutrons? 2) An atom of Silver (Ag) has a mass number of 115. How many protons, neutrons, and electrons are there in this atom of Silver? AZ Notation A mass number X chemical symbol Z atomic number Another type of notation: Whenever you see a dash present between a chemical symbol and a number, you can be assured that number is the mass number of that particular atom. C-12 C-14 C-13 Proton: ____ Proton: ____ Proton: ____ Neutrons: ____ Neutrons: ____ Neutrons: ____ Electrons: ____ Electrons: ____ Electrons: ____ 3 4 3 Matter has mass and occupies volume. Mass: refers to the amount of matter. Volume: refers to the amount of space occupied by matter. Tennis balls are much larger than golf balls, and therefore have a larger volume than golf balls do since they occupy more space. Tennis balls have less mass than golf balls, though. Why? Review Identify the subatomic particles present in an atom of ²²⁶Ra. Video: Crash Course Chemistry: The Nucleus