Copyright © Houghton Mifflin Company. All rights reserved. 4 | 1 Dalton’s Atomic Theory Elements are composed of tiny particles called atoms. All atoms of a given element are identical. –All carbon atoms have the same chemical and physical properties. Atoms of a given element are different from those of any other element. –Carbon atoms have different chemical and physical properties than sulfur atoms.

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 2 Symbols for the Elements Symbolized with one or two letters First letter is capitalized, second is small Carbon: C Bromine: Br Common elements and symbols in Table 4.3

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 3 Elements Robert Boyle ( ) Elements: cannot be broken down into atwo or more simpler substances 155 elements: 88 natural

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 4 Dalton’s Atomic Theory Atoms of different elements combine to form compounds.

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 5 Dalton’s Atomic Theory Law of Constant Composition: all samples of a compound contain the same proportions (by mass) of the elements that form the compound. Atoms are indivisible by chemical processes. –All atoms present at beginning are present at the end. –Atoms are not created or destroyed, just rearranged in chemical reactions. –Atoms of one element cannot change into atoms of another element. Cannot turn lead into gold by a chemical reaction

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 6 Writing Formulas of Compounds Each element is represented by its symbol. The number of each type of atom is indicated by a subscript written to the right of the element symbol. If only one atom is present, do not include a subscript. If polyatomic groups are present in the molecule, they are written inside parentheses if more than one group is present. Examples: H 2 O, NaCl, KNO 3, Mg(NO 3 ) 2

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 7 J. J. Thomson’s “plumb pudding” model of the atom (1910) Atom contains positive particles that balance the negative charge of the electrons.

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 8 Rutherford’s Gold Foil Experiment

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 9 Rutherford’s Nuclear Model (1911) The atom contains a tiny dense center called the nucleus. The nucleus is essentially the entire mass of the atom. The nucleus is positively charged. –It is composed of protons (positive charge) and neutrons (no charge) – balances the negative charge of the electrons. The electrons move around in the empty space of the atom surrounding the nucleus.

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 10 The Modern Atom (cont.)

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 11 Components of an Atom

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 12 The Modern Atom Atoms are composed of three main pieces: protons, neutrons, and electrons. The nucleus contains protons and neutrons. the hydrogen atom (H) the helium atom (He)

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 13 Isotopes All atoms of an element have the same number of protons. The number of protons in an atom of a given element is the same as the atomic number. –Found on the periodic table Atoms of an element with different numbers of neutrons are called isotopes.

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 14 Isotopes (cont.) All isotopes of an element are chemically identical. –Undergo the exact same chemical reactions Isotopes of an element have different masses. Isotopes are identified by their mass numbers. –Mass number = # of protons + # of neutrons Isotope symbols: X = the symbol of the element A = the mass number Z = the atomic number (number of protons) A - Z = # of neutrons

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 15 Isotope Examples SymbolNumber of Protons Number of Electrons Number of Neutrons

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 16 Other Examples SymbolNumber of Protons Number of Electrons Number of Neutrons

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 17 The Modern Periodic Table

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 18 Properties of Metals Good conductors of heat and electricity Malleability (thin sheets) Ductility (wires) Shiny All are solids at room temperature except mercury (Hg)

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 19 Properties of Nonmetals Poor conductors Not malleable or ductile Exist in various physical states: solids – carbon, phosphorus liquids – bromine gases – hydrogen, oxygen, helium

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 20 Metalloids Show a mixture of metallic and nonmetallic properties Examples:

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 21 Problem Give the symbol and classify as a metal, nonmetal or metalloid: Silver Sulfur Silicon Barium

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 22 Natural States of Elements Most elements are solids at room temperature. Group 8 Noble gases: Diatomic molecules:

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 23 Diatomic Molecules ElementElemental State (25 o C)Molecule hydrogencolorless gasH2H2 nitrogencolorless gasN2N2 oxygenpale blue gasO2O2 fluorinepale yellow gasF2F2 chlorinepale green gasCl 2 brominereddish brown liquidBr 2 iodinepurple solidI2I2

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 24 Allotropes of Carbon

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 25 Ions Cations: ions that have a positive charge –Form when an atom loses electrons Anions: ions that have a negative charge –Form when an atom gains electrons Cations and anions attract each other.

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 26 Atomic Structures of Ions Metals form cations. For each positive charge the ion has 1 less electron than the neutral atom. –Na = 11 e -, Na + = 10 e - –Ca = 20 e -, Ca +2 = 18 e - Cations are named the same as the metal. sodiumNa  Na + + 1e - sodium ion calciumCa  Ca e - calcium ion

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 27 Atomic Structures of Ions (cont.) Nonmetals form anions. For each negative charge the ion has 1 more electron than the neutral atom. –F = 9 e -, F - = 10 e - –P = 15 e -, P 3- = 18 e - Anions are named by changing the ending of the name to –ide. –FluorineF + 1e -  F - fluoride ion –OxygenO + 2e -  O 2- oxide ion

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 28 Ionic Charges and Compounds Charges on the ions of some elements can be predicted from the periodic table. Cations and anions usually form simultaneously to yield an ionic compound. When ions are formed the number of protons and neutrons does not change. There must be a net charge of zero.

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 29 Ionic Charges and Compounds (cont.)

Copyright © Houghton Mifflin Company. All rights reserved. 4 | 30 Formulas of Ionic Compounds The formula of an ionic compound can be determined by balancing the positive charge of the cation(s) with the negative charge of the anion(s) to yield a net charge of zero. Ba 2+ and Cl - K + and P 3- Ca 2+ and O 2- Mg 2+ and N 3-