The Atom: Atomic Number , Mass Number and Isotopes LecturePLUS Timberlake

Atomic Theory Atoms are building blocks of elements Similar atoms in each element Different from atoms of other elements Two or more different atoms bond in simple ratios to form compounds LecturePLUS Timberlake

Subatomic Particles Particle Symbol Charge Relative Mass Electron e- 1- 0 Proton p+ 1+ 1amu Neutron n 0 1amu LecturePLUS Timberlake

Location of Subatomic Particles 10-13 cm electrons protons neutrons 10-8 cm nucleus LecturePLUS Timberlake

Counts the number of protons in an atom Atomic Number (Z) Counts the number of protons in an atom LecturePLUS Timberlake

Atomic Number on the Periodic Table 11 Na Atomic Number Symbol LecturePLUS Timberlake

All atoms of an element have the same number of protons 11 Na 11 protons Sodium LecturePLUS Timberlake

Learning Check AT 1 State the number of protons for atoms of each of the following: A. Nitrogen 1) 5 protons 2) 7 protons 3) 14 protons B. Sulfur 1) 32 protons 2) 16 protons 3) 6 protons C. Barium 1) 137 protons 2) 81 protons 3) 56 protons LecturePLUS Timberlake

Solution AT 1 State the number of protons for atoms of each of the following: A. Nitrogen 2) 7 protons B. Sulfur 2) 16 protons C. Barium 3) 56 protons LecturePLUS Timberlake

Number of Electrons An atom is neutral The net charge is zero Number of protons = Number of electrons Atomic number = Number of electrons LecturePLUS Timberlake

Counts the number of protons and neutrons in an atom Mass Number (A) Counts the number of protons and neutrons in an atom LecturePLUS Timberlake

Atomic Symbols Show the mass number and atomic number Give the symbol of the element mass number 23 Na sodium-23 atomic number 11 LecturePLUS Timberlake

More Atomic Symbols 16 31 65 8 15 30 O P Zn 8 p+ 15 p+ 30 p+ 16 31 65 O P Zn 8 15 30 8 p+ 15 p+ 30 p+ 8 n 16 n 35 n 8 e- 15 e- 30 e- LecturePLUS Timberlake

Isotopes Atoms with the same number of protons, but different numbers of neutrons. Atoms of the same element (same atomic number) with different mass numbers Isotopes of chlorine 35Cl 37Cl 17 17 chlorine - 35 chlorine - 37 LecturePLUS Timberlake

Learning Check AT 2 6 6 6 #P _______ _______ _______ Naturally occurring carbon consists of three isotopes, 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of these carbon atoms. 12C 13C 14C 6 6 6 #P _______ _______ _______ #N _______ _______ _______ #E _______ _______ _______ LecturePLUS Timberlake

Solution AT 2 6 6 6 #P __6___ _ 6___ ___6___ #N __6___ _ _7___ ___8___ 12C 13C 14C 6 6 6 #P __6___ _ 6___ ___6___ #N __6___ _ _7___ ___8___ #E __6___ _ 6___ ___6___ LecturePLUS Timberlake

Learning Check AT 3 An atom of zinc has a mass number of 65. A. Number of protons in the zinc atom 1) 30 2) 35 3) 65 B. Number of neutrons in the zinc atom C. What is the mass number of a zinc isotope with 37 neutrons? 1) 37 2) 65 3) 67 LecturePLUS Timberlake

Solution AT 3 An atom of zinc has a mass number of 65. A. Number of protons in the zinc atom 1) 30 B. Number of neutrons in the zinc atom 2) 35 C. What is the mass number of a zinc isotope with 37 neutrons? 3) 67 LecturePLUS Timberlake

Learning Check AT 4 Write the atomic symbols for atoms with the following: A. 8 p+, 8 n, 8 e- ___________ B. 17p+, 20n, 17e- ___________ C. 47p+, 60 n, 47 e- ___________ LecturePLUS Timberlake

Solution AT 4 B. 17p+, 20n, 17e- 37Cl 17 47 16O A. 8 p+, 8 n, 8 e- 8 C. 47p+, 60 n, 47 e- 107Ag 47 LecturePLUS Timberlake

Learning Check AT 5 An atom has 14 protons and 20 neutrons. A. Its atomic number is 1) 14 2) 16 3) 34 B. Its mass number is C. The element is 1) Si 2) Ca 3) Se D. Another isotope of this element is 1) 34X 2) 34X 3) 36X 16 14 14 LecturePLUS Timberlake

Solution AT 5 An atom has 14 protons and 20 neutrons. A. It has atomic number 1) 14 B. It has a mass number of 3) 34 C. The element is 1) Si D. Another isotope of this element would be 3) 36X 14 LecturePLUS Timberlake

Masses of Atoms A scale designed for atoms gives their small atomic masses in atomic mass units (amu) An atom of 12C was assigned an exact mass of 12.00 amu Relative masses of all other atoms was determined by comparing each to the mass of 12C An atom twice as heavy has a mass of 24.00 amu. An atom half as heavy is 6.00 amu. LecturePLUS Timberlake

Na 22.99 Atomic Mass Listed on the periodic table Gives the mass of “average” atom of each element compared to 12C Average atom based on all the isotopes and their abundance % Atomic mass is not a whole number LecturePLUS Timberlake

Learning Check AT6 Using the periodic table, specify the atomic mass of each element (round to the tenths place): A. calcium __________ B. aluminum __________ C. lead __________ D. barium __________ E. iron __________ LecturePLUS Timberlake

Solution AT6 Using the periodic table, specify the atomic mass of each element (round to the tenths place): A. calcium _40.1 amu _ B. aluminum _27.0 amu _ C. lead _207.2 amu_ D. barium _137.3 amu_ E. iron _55.8 amu__ LecturePLUS Timberlake

Atomic Mass of Magnesium Isotopes Mass of Isotope Abundance 24Mg = 24.0 amu 78.70% 25Mg = 25.0 amu 10.13% 26Mg = 26.0 amu 11.17% Atomic mass (average mass) Mg = 24.3 amu Mg 24.3 LecturePLUS Timberlake