Chapter 3 Atoms and Elements

Classification of Matter

Elements Elements are Pure substances that cannot be separated into simpler substances by ordinary laboratory processes The building blocks of matter gold (Au) carbon (C) aluminum (Al) Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings **Memorize the symbols of the first 36 elements!!

Periodic Table Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Groups and Periods Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Names of Some Representative Elements Several groups of representative elements are known by common names. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Identify the element described by the following: A. Group 7A(17), Period 4 1) Br 2) Cl 3) Mn B. Group 2A(2), Period 3 1) beryllium 2) magnesium 3) boron C. Group 5A(15), Period 2 1) phosphorus 2) arsenic 3) nitrogen

Solution A. Group 7A, Period 4 1) Br B. Group 2A, Period 3 2) magnesium C. Group 5A(15), Period 2 3) nitrogen

Metals, Nonmetals, and Metalloids The heavy zigzag line separates metals and nonmetals. Metals are located to the left. Nonmetals are located to the right. Metalloids are located along the heavy zigzag line between the metals and nonmetals. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Comparing a Metal, Metalloid, and Nonmetal

Dalton’s Atomic Theory Matter is composed of tiny particles called atoms. Atoms of each element are similar, and different from atoms of other elements. Atoms of two or more different elements combine to form compounds. A chemical reaction involves changes in the arrangement or combination of atoms. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Rutherford’s Gold-Foil Experiment Positively charged particles were aimed at atoms of gold Most went straight through the atoms Only a few were deflected Conclusion: There must be a small, dense, positively charged nucleus in the atom that deflects positive particles that come close. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Structure of the Atom An atom consists Of a nucleus that contains protons and neutrons Of electrons in a large empty space around the nucleus Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Particles in the Atom

Atomic Number 11 Na Atomic Number Symbol The atomic number Is specific for each element (DEFINES an element) Is the same for all atoms of an element Is equal to the number of protons in an atom Appears above the symbol of an element 11 Na Atomic Number Symbol

State the number of protons in each: A. A nitrogen atom 1) 5 protons 2) 7 protons 3) 14 protons B. A sulfur atom 1) 32 protons 2) 16 protons 3) 6 protons C. A barium atom 1) 137 protons 2) 81 protons 3) 56 protons

Solution State the number of protons in each: A. A nitrogen atom 2) atomic number 7; 7 protons B. A sulfur atom 2) atomic number 16; 16 protons C. A barium atom, 3) atomic number 56; 56 protons

Electrons in an Atom An atom of any element is electrically neutral; the net charge of an atom is zero. In an atom, the number of protons is equal to the number of electrons. number of protons = number of electrons For example, an atom of aluminum has 13 protons and 13 electrons. The net charge is zero. 13 protons (13 +) + 13 electrons (13 -) = 0

Mass Number The mass number Represents the number of particles in the nucleus Is equal to the Number of protons + Number of neutrons

An atom of zinc has a mass number of 65. A. How many protons are in this zinc atom? 1) 30 2) 35 3) 65 B. How many neutrons are in the zinc atom? C. What is the mass number of a zinc atom that has 37 neutrons? 1) 37 2) 65 3) 67

Solution An atom of zinc has a mass number of 65. A. How many protons are in this zinc atom? 1) 30 (atomic number 30) B. How many neutrons are in the zinc atom? 2) 35 (65 – 30 = 35) C. What is the mass number of a zinc atom that has 37 neutrons? 3) 67 (30 + 37 = 67)

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

Solution An atom has 14 protons and 20 neutrons. A. Its atomic number is 1) 14 B. It has a mass number of 3) 34 (14 + 20 = 34) C. The element is 1) Si (Atomic number 14)

Nuclear Symbols From the nuclear symbol, we can determine the number of protons (p+), neutrons, (n), and electrons (e-) in a particular atom. 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- Mass number Atomic number

Isotopes Isotopes Are atoms of the same element that have different mass numbers Have the same number of protons, but different numbers of neutrons

Naturally occurring carbon consists of three isotopes, 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of the following: 12C 13C 14C 6 6 6 protons ______ ______ ______ neutrons ______ ______ ______ electrons ______ ______ ______

Solution Naturally occurring carbon consists of three isotopes, 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of the following: 12C 13C 14C 6 6 6 protons 6 p+ 6 p+ 6 p+ neutrons 6 n 7 n 8 n electrons 6 e- 6 e- 6 e-

Write the nuclear symbols for atoms with the following subatomic particles: A. 8 p+, 8 n, 8 e- ___________ B. 17p+, 20n, 17e- ___________ C. 47p+, 60 n, 47 e- ___________

Solution Write the nuclear symbols for atoms with the following subatomic particles: 16O A. 8 p+, 8 n, 8 e- 8 B. 17p+, 20 n, 17e- 37Cl 17 C. 47p+, 60 n, 47 e- 107Ag 47

Atomic Mass Na 22.99 The atomic mass of an element Is listed below the symbol of each element on the periodic table Gives the mass of an “average” atom of each element compared to 12C Is not the same as the mass number Na 22.99

Atomic Mass for Cl The atomic mass of chlorine is the weighted average of two isotopes 35Cl and 37Cl. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Calculating Atomic Mass for Cl 35Cl has atomic mass 34.97 (75.78%) and 37C has atomic mass 36.97 (24.22%). The atomic mass and percent of each isotope are used to calculate the contribution of each isotope to the weighted average. 34.97 x 75.78 = 26.50 amu 100 35.97 x 24.22 = 8.953 amu 100 35.453 amu The sum is the weighted average or atomic mass Cl = 35.45 amu

Examples of Isotopes and Atomic Masses Most elements have two or more isotopes that contribute to the atomic mass of that element.

Gallium is an element found in small lasers used in compact disc players. In a sample of gallium, there is 60.11% of 69Ga (atomic mass 68.93) atoms and 39.89% of 71Ga (atomic mass 70.93) atoms. What is the atomic mass of gallium?

Solution 69Ga 68.93 amu x 60.11 = 41.43 amu (from 69Ga) 100 71Ga Atomic mass Ga = 69.72 amu 31 Ga 69.72