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4.3. Atomic Number. Atomic Number What makes one element different from another?. 4.3. Atomic Number. Elements are different because they contain different numbers of protons . The atomic number of an element is the number of protons in the nucleus of an atom of that element. 4.3.
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4.3 Atomic Number • Atomic Number • What makes one element different from another?
4.3 Atomic Number • Elements are different because they contain different numbers of protons. • The atomic numberof an element is the number of protons in the nucleus of an atom of that element.
4.3 Atomic Number
4.3 Mass Number • Mass Number • How do you find the number of neutrons in an atom?
4.3 Mass Number • The total number of protons and neutrons in an atom is called the mass number. • The number of neutrons in an atom is the difference between the mass number and atomic number.
4.3 Mass Number • Au is the chemical symbol for gold.
4.3 Isotopes • Isotopes • How do isotopes of an element differ?
4.3 Isotopes • Isotopes are atoms that have the same number of protons but different numbers of neutrons. • Because isotopes of an element have different numbers of neutrons, they also have different mass numbers.
4.3 Isotopes • Despite these differences, isotopes are chemically alike because they have identical numbers of protons and electrons.
4.3 Atomic Mass • Atomic Mass • How do you calculate the atomic mass of an element?
4.3 Atomic Mass • It is useful to compare the relative masses of atoms to a standard reference isotope. Carbon-12 is the standard reference isotope. Cabon-12 has a mass of exactly 12 atomic mass units. • An atomic mass unit (amu)is defined as one twelfth of the mass of a carbon-12 atom. It is based on the mass of a proton or neutron. • 1 gram = 6.02 x 1023 amu’s (Avagadro’s number) • 1 amu = 1.67 x 10-24 grams
4.3 Atomic Mass • Some Elements and Their Isotopes
4.3 Atomic Mass • The atomic massof an element is a weighted average mass of the atoms in a naturally occurring sample of the element. • A weighted average mass reflects both the mass and the relative abundance of the isotopes as they occur in nature.
4.3 Atomic Mass • Weighted Average Mass of a Chlorine Atom
for Conceptual Problem 4.3 for Conceptual Problem 4.3
4.3 Atomic Mass • To calculate the atomic mass of an element, multiply the mass of each isotope by its percent relative abundance, expressed as a decimal, and then add the products.
4.3 Atomic Mass • For example, carbon has two stable isotopes: • Carbon-12, which has a relative abundance of 98.89%, and • Carbon-13, which has a relative abundance of 1.11%.
4.3 The Periodic Table—A Preview • The Periodic Table—A Preview • Why is a periodic table useful?
4.3 The Periodic Table—A Preview • A periodic table is an arrangement of elements in which the elements are separated into groups based on a set of repeating properties. • A periodic table allows you to easily compare the properties of one element (or a group of elements) to another element (or group of elements).
4.3 The Periodic Table—A Preview • The Periodic Table
4.3 The Periodic Table—A Preview • Each horizontal row of the periodic table is called a period. • Within a given period, the properties of the elements vary as you move across it from element to element.
4.3 The Periodic Table—A Preview • A Period
4.3 The Periodic Table—A Preview • Each vertical column of the periodic table is called a group, or family. • Elements within a group have similar chemical and physical properties.
4.3 The Periodic Table—A Preview • A Group or Family
4.3 Section Quiz • 1. Isotopes of an element have • the same mass number. • different atomic numbers. • the same number of protons but different numbers of neutrons. • the same number of protons but different numbers of electrons.
4.3 Section Quiz • 2. How many neutrons are in sulfur-33? • 16 neutrons • 33 neutrons • 17 neutrons • 32.06 neutrons
4.3 Section Quiz • 3. If sulfur contained 90.0% sulfur-32 and 10.0% sulfur-34, its atomic mass would be • 32.2 amu. • 32.4 amu. • 33.0 amu. • 35.4 amu.
