Chapter 3Atoms and Elements 3.1 Elements and Symbols Elements are pure substances that cannot be separated into simpler substances by ordinary laboratory processes. the building blocks of matter. gold carbon aluminum 1

Sources of Some Element Names Some elements are named for planets, mythological figures, minerals, colors, scientists, and places. A symbol represents the name of an element. consists of 1 or 2 letters. starts with a capital letter With few elements use their own special symbols 2 1-Letter Symbols 2-Letter Symbols C carbon Co cobalt N nitrogenCa calcium SsulfurAu gold Mg magnesium

Physical Properties of Elements Some physical properties of copper are: ColorRed-orange LusterVery shiny Melting point1083 °C Boiling point2567 °C Conduction of electricityExcellent Conduction of heatExcellent 3

Example Select the correct symbol for each. A. Phosphorous 1) K2) P3) Ph Select the correct name for each symbol. A. Ne 1) neon 2) nitrogen 3) nickel B. K 1) potassium 2) phlogiston3) phosphorus 4

Development of the Periodic Table Mendeleev’s Periodic Table (1871) Until the discovery of the proton, the elements were typically organized by increasing atomic weight. The modern organization is by increasing atomic number. 3.3The Periodic Table

Groups and Periods On the periodic table, elements are arranged according to similar properties. groups contain elements with similar properties in vertical columns. periods are horizontal rows of elements. 6

Names of Some Representative Elements Group Numbers use the letter A for the representative elements (1A to 8A) and the letter B for the transition elements. also use numbers 1-18 to the columns from left to right.

Elements and the Periodic Table

Examples Identify the element described by the following: A. Group 7A (17), Period 4 1) Br2) Cl3) Mn B. Group 2A (2), Period 3 1) beryllium2) boron 3) magnesium C. Group 5A (15), Period 2 1) phosphorus 2) arsenic3) nitrogen 9

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. 10

Metals, Nonmetals, and Metalloids on the Periodic Table 11 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.

Physical properties Metals are shiny and ductile. are good conductors of heat and electricity. Nonmetals are dull, brittle, and poor conductors. are good insulators. Metalloids are better conductors than nonmetals, but not as good as metals. are used as semiconductors and insulators.

Periods: 7 horizontal rows. Groups: 18 vertical columns. International standard: 1-18 US system: 1A-8A, 1B-8B SUMMARY

Examples Identify each of the following elements as 1) metal, 2) nonmetal, or 3) metalloid. A. sodium____ B. iodine____ C. Argon ____ D. iron____ E. Silicon____ 14

The Law of Multiple Proportions and Dalton’s Atomic Theory Elements are made up of tiny particles called atoms. Each element is characterized by the mass of its atoms. Atoms of the same element have the same mass, but atoms of different elements have different masses. The chemical combination of elements to make different chemical compounds occurs when atoms join in small whole- number ratios. Chemical reactions only rearrange how atoms are combined in chemical compounds; the atoms themselves don’t change. 3.4 The Atom

Atomic Structure: Electrons Cathode-Ray Tubes: J. J. Thomson ( ) proposed that cathode rays must consist of tiny negatively charged particles. We now call them electrons.

Rutherford’s Gold Foil Experiment In Rutherford’s gold foil experiment, positively charged particles were aimed at atoms of gold. mostly went straight through the atoms. were deflected only occasionally. Conclusion: There must be a small, dense, positively charged nucleus in the atom that deflects positive particles that come close.

Subatomic Particles Atoms contain subatomic particles. Protons have a positive (+) charge. Electrons have a negative (-) charge. Neutrons are neutral. Like charges repel and unlike charges attract.

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.

Atomic Mass Scale On the atomic mass scale, 1 atomic mass unit (amu) has a mass equal to 1/12 of the mass of the carbon-12 atom. a proton has a mass of about 1 (1.007) amu. a neutron has a mass of about 1 (1.008) amu. an electron has a very small mass, amu. 20

Examples Identify each statement as describing a 1) proton, 2) neutron, or 3) electron. A. found outside the nucleus B. has a positive charge C. is neutral D. found in the nucleus 21

Examples Is each of the following statements true or false? ◦ Protons are heavier than electrons ◦ Protons are attracted to neutrons ◦ Electrons are small that they have no electrical charge ◦ The nucleus contains all the protons and neutrons of an atom 22

3.5 Atomic Number and Mass Number The atomic number is specific for each 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. 23

Atomic Number and Protons What is the atomic number, number of proton and electrons in H atom: Na atom: Co atom: Se atom: 24

Electrons in An Atom An atom of an element is electrically neutral; the net charge of an atom is zero. has an equal number of protons and electrons. number of protons = number of electrons Aluminum has 13 protons and 13 electrons. The net (overall) charge is zero. 13 protons + 13 electrons = 0 (+13) + (-13) = 0 (neutral) 25

Mass Number The mass number represents the number of particles in the nucleus. is equal to the number of protons + the number of neutrons. 26 ElementSymbolAtomic number Mass number p+e-n0n0 CarbonC Chlorine37 Gold79

Examples An atom of zinc has a mass number of 65. A. How many protons are in this zinc atom? 1) 302) 353) 65 B. How many neutrons are in the zinc atom? 1) 302) 353) 65 C. What is the mass number of a zinc atom that has 37 neutrons? 1) 372) 653) 67 27

3.6 Isotopes and Atomic Mass Isotopes are atoms of the same element that have different mass numbers. have the same number of protons, but different numbers of neutrons. Isoptic symbol 28 gives the mass number in the upper left corner and the atomic number in the lower left corner

Information from Atomic Symbols Examples of number of subatomic particles for atoms Atomic symbol O P Zn p + 15 p + …. p + 8 n16 n ……n 8 e - 15 e - ….. e - 29

Examples Naturally occurring carbon consists of three isotopes: 12 C, 13 C, and 14 C. State the number of protons, neutrons, and electrons in each of the following: 12 C 13 C 14 C protons ______ ______ ______ neutrons ______ ______ ______ electrons______ ______ ______ 30

Examples Write the atomic 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 - ___________ 31

Atomic Mass 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 12 C. is not the same as the mass number. has the smallest unit of amu 32 Na 22.99

Examples Using the periodic table, specify the atomic mass of each element. A.calcium__________ B. aluminum__________ C. lead__________ D. barium__________ E. iron__________ 33

Isotopes of Sulfur A sample of naturally occurring sulfur contains several isotopes with the following abundances Isotope % abundance 32 S S S S S, 33 S, 34 S, 36 S Average mass of S is amu

Calculating Atomic Mass The calculation for atomic mass requires the percent(%) abundance of each isotope. atomic mass of each isotope of that element. sum of the weighted averages. 35 Report your answer to two decimal places

Atomic Masses carbon-12:98.89 % natural abundance12.00 amu carbon-13:1.11 % natural abundance amu Why is the atomic mass of the element carbon amu? = amu mass of carbon = (12 amu)(0.9889) + ( amu)( ) = amu amu

Atomic Mass for Cl The atomic mass of chlorine is due to all the Cl isotopes. not a whole number. the average of two isotopes: 35 Cl and 37 Cl. 37

Calculating Atomic Mass for Cl 35 Cl has atomic mass amu (75.76%) and 37 Cl has atomic mass amu (24.24%). Use atomic mass and percent of each isotope to calculate the contribution of each isotope to the weighted average. Atomic mass 35 Cl x % abundance = Atomic mass 37 Cl x % abundance = Sum is atomic mass of Cl is 38