Chapter 3Atoms and Elements 1

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 2

Sources of Some Element Names Some elements are named for planets, mythological figures, minerals, colors, scientists, and places. 3 TABLE 3.1

Symbols of Elements A symbol represents the name of an element. consists of 1 or 2 letters. starts with a capital letter. 1-Letter Symbols 2-Letter Symbols C carbon Co cobalt N nitrogenCa calcium F fluorine Al aluminum O oxygen Mg magnesium 4

Symbols from Latin Names Several symbols are derived from Latin names as shown below. Cu, copper (cuprum) Au, gold (aurum) Fe, iron (ferrum) Ag, silver (argentum) 5

Physical Properties of Elements The physical properties of an element are observed or measured without changing its identity. include the following: Shape Density ColorMelting point Odor and tasteBoiling point 6

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 7

Example Select the correct symbol for each. A. Phosphorous 1) K2) P3) Ph B. Aluminum 1) Al2) Au3) An C. Iron 1) Ir2) FE3) Fe 8

Examples Select the correct name for each symbol. A. Ne 1) neon 2) nitrogen 3) nickel B. K 1) potassium 2) phlogiston3) phosphorus C. Au 1) silver 2) agean3) gold 9

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. 11

Groups and Periods 12

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

Alkali Metals Group 1A (1), the alkali metals, includes lithium, sodium, and potassium.

Halogens Group 7A (17), the halogens, includes chlorine, bromine, and iodine.

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 18

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. 19

Metals, Nonmetals, and Metalloids on the Periodic Table 20

Properties of Metals, Nonmetals, and Metalloids 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. 21

Comparing a Metal, Metalloid, and Nonmetal 22 TABLE 3.4

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____ 24

Examples Match the elements to the description. A. Metals in Group 4A (14) 1) Sn, Pb 2) C, Si 3) C, Si, Ge, Sn B. Nonmetals in Group 5A (15) 1) As, Sb, Bi 2) N, P3) N, P, As, Sb C. Metalloids in Group 4A (14) 1) C, Si, Ge, 2) Si, Ge 3) Si, Ge, Sn, Pb 25

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 Copyright © 2009 by Pearson Education, Inc.

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. 32

Particles in the Atom TABLE 3.5

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 34

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 35