The Atom 1) NucleonsNucleons 2) IsotopesIsotopes 6) Electron ConfiguationElectron Configuation 7) Development of the Atomic ModelDevelopment of the Atomic Model

(c) 2006, Mark Rosengarten Nucleons 4 Protons: +1 each, determines identity of element, mass of 1 amu, determined using atomic number, nuclear charge 4 Neutrons: no charge, determines identity of isotope of an element, 1 amu, determined using mass number - atomic number (amu = atomic mass unit) S and S are both isotopes of S 4 S-32 has 16 protons and 16 neutrons 4 S-33 has 16 protons and 17 neutrons 4 All atoms of S have a nuclear charge of +16 due to the 16 protons.

Isotopes 4 Atoms of the same element MUST contain the same number of protons. 4 Atoms of the same element can vary in their numbers of neutrons, therefore many different atomic masses can exist for any one element. These are called isotopes. 4 The atomic mass on the Periodic Table is the weight- average atomic mass, taking into account the different isotope masses and their relative abundance.weight- average atomic mass 4 Rounding off the atomic mass on the Periodic Table will tell you what the most common isotope of that element is.common isotope of that element

Weight-Average Atomic Mass 4 WAM = ((% A of A/100) X Mass of A) + ((% A of B/100) X Mass of B) + … 4 What is the WAM of an element if its isotope masses and abundances are: –X-200: Mass = amu, % abundance = 20.0 % –X-204: Mass = amu, % abundance = 80.0% –amu = atomic mass unit ( 1.66 × kilograms/amu)

(c) 2006, Mark Rosengarten Most Common Isotope 4 The weight-average atomic mass of Zinc is amu. What is the most common isotope of Zinc? Zn-65! 4 What are the most common isotopes of: –CoAg –SPb 4 FACT: one atomic mass unit (1.66 × kilograms) is defined as 1/12 of the mass of an atom of C This method doesn’t always work, but it usually does. Use it for the Regents exam.

(c) 2006, Mark Rosengarten Electron Configuration 4 Basic Configuration Basic Configuration 4 Valence Electrons Valence Electrons 4 Electron-Dot (Lewis Dot) Diagrams Electron-Dot (Lewis Dot) Diagrams 4 Excited vs. Ground State Excited vs. Ground State 4 What is Light? What is Light?

(c) 2006, Mark Rosengarten Basic Configuration 4 The number of electrons is determined from the atomic number. 4 Look up the basic configuration below the atomic number on the periodic table. (PEL: principal energy level = shell) 4 He: 2 (2 e - in the 1st PEL) 4 Na: (2 e - in the 1st PEL, 8 in the 2nd and 1 in the 3rd) 4 Br: (2 e - in the 1st PEL, 8 in the 2nd, 18 in the 3rd and 7 in the 4th)

(c) 2006, Mark Rosengarten Valence Electrons 4 The valence electrons are responsible for all chemical bonding. 4 The valence electrons are the electrons in the outermost PEL (shell). 4 He: 2 (2 valence electrons) 4 Na: (1 valence electron) 4 Br: (7 valence electrons) 4 The maximum number of valence electrons an atom can have is EIGHT, called a STABLE OCTET.

(c) 2006, Mark Rosengarten Electron-Dot Diagrams 4 The number of dots equals the number of valence electrons. 4 The number of unpaired valence electrons in a nonmetal tells you how many covalent bonds that atom can form with other nonmetals or how many electrons it wants to gain from metals to form an ion. 4 The number of valence electrons in a metal tells you how many electrons the metal will lose to nonmetals to form an ion. Caution: May not work with transition metals. 4 EXAMPLE DOT DIAGRAMS EXAMPLE DOT DIAGRAMS

(c) 2006, Mark Rosengarten Example Dot Diagrams Carbon can also have this dot diagram, which it has when it forms organic compounds.

(c) 2006, Mark Rosengarten Excited vs. Ground State 4 Configurations on the Periodic Table are ground state configurations. 4 If electrons are given energy, they rise to higher energy levels (excited state). 4 If the total number of electrons matches in the configuration, but the configuration doesn’t match, the atom is in the excited state. 4 Na (ground, on table): Example of excited states: 2-7-2, , 2-6-3

(c) 2006, Mark Rosengarten Development of the Atomic Model 4 Thompson Model Thompson Model 4 Rutherford Gold Foil Experiment and Model Rutherford Gold Foil Experiment and Model 4 Bohr Model Bohr Model 4 Quantum-Mechanical Model Quantum-Mechanical Model

(c) 2006, Mark Rosengarten Thompson Model 4 The atom is a positively charged diffuse mass with negatively charged electrons stuck in it.

(c) 2006, Mark Rosengarten Rutherford Model 4 The atom is made of a small, dense, positively charged nucleus with electrons at a distance, the vast majority of the volume of the atom is empty space. Alpha particles shot at a thin sheet of gold foil: most go through (empty space). Some deflect or bounce off (small + charged nucleus).

(c) 2006, Mark Rosengarten Bohr Model 4 Electrons orbit around the nucleus in energy levels (shells). Atomic bright-line spectra was the clue.

(c) 2006, Mark Rosengarten Quantum-Mechanical Model 4 Electron energy levels are wave functions. 4 Electrons are found in orbitals, regions of space where an electron is most likely to be found. 4 You can’t know both where the electron is and where it is going at the same time. 4 Electrons buzz around the nucleus like gnats buzzing around your head.

(c) 2006, Mark Rosengarten Types of Matter 4 Substances (Homogeneous) –Elements (cannot be decomposed by chemical change): Al, Ne, O, Br, HElements –Compounds (can be decomposed by chemical change): NaCl, Cu(ClO 3 ) 2, KBr, H 2 O, C 2 H 6Compounds 4 Mixtures Mixtures –Homogeneous: Solutions (solvent + solute) –Heterogeneous: soil, Italian dressing, etc.

(c) 2006, Mark Rosengarten Elements 4 A sample of lead atoms (Pb). All atoms in the sample consist of lead, so the substance is homogeneous. 4 A sample of chlorine atoms (Cl). All atoms in the sample consist of chlorine, so the substance is homogeneous.

(c) 2006, Mark Rosengarten Compounds 4 Lead has two charges listed, +2 and +4. This is a sample of lead (II) chloride (PbCl 2 ). Two or more elements bonded in a whole-number ratio is a COMPOUND. 4 This compound is formed from the +4 version of lead. This is lead (IV) chloride (PbCl 4 ). Notice how both samples of lead compounds have consistent composition throughout? Compounds are homogeneous!

(c) 2006, Mark Rosengarten Mixtures 4 A mixture of lead atoms and chlorine atoms. They exist in no particular ratio and are not chemically combined with each other. They can be separated by physical means. 4 A mixture of PbCl 2 and PbCl 4 formula units. Again, they are in no particular ratio to each other and can be separated without chemical change.

(c) 2006, Mark Rosengarten The Periodic Table 4 Metals Metals 4 Nonmetals Nonmetals 4 Metalloids Metalloids 4 Chemistry of Groups Chemistry of Groups 4 Electronegativity Electronegativity 4 Ionization Energy Ionization Energy

(c) 2006, Mark Rosengarten Metals 4 Have luster, are malleable and ductile, good conductors of heat and electricity 4 Lose electrons to nonmetal atoms to form positively charged ions in ionic bonds Lose electrons to nonmetal atoms to form positively charged ionsionic bonds 4 Large atomic radii compared to nonmetal atoms 4 Low electronegativity and ionization energyelectronegativityionization energy 4 Left side of the periodic table (except H)

(c) 2006, Mark Rosengarten Nonmetals 4 Are dull and brittle, poor conductors 4 Gain electrons from metal atoms to form negatively charged ions in ionic bonds Gain electrons from metal atoms to form negatively charged ions 4 Share unpaired valence electrons with other nonmetal atoms to form covalent bonds and moleculescovalent bonds 4 Small atomic radii compared to metal atoms 4 High electronegativity and ionization energyelectronegativityionization energy 4 Right side of the periodic table (except Group 18)

(c) 2006, Mark Rosengarten Metalloids 4 Found lying on the jagged line between metals and nonmetals flatly touching the line (except Al and Po). 4 Share properties of metals and nonmetals (Si is shiny like a metal, brittle like a nonmetal and is a semiconductor).

(c) 2006, Mark Rosengarten Chemistry of Groups 4 Group 1: Alkali Metals Group 1: Alkali Metals 4 Group 2: Alkaline Earth Metals Group 2: Alkaline Earth Metals 4 Groups 3-11: Transition Elements Groups 3-11: Transition Elements 4 Group 17: Halogens Group 17: Halogens 4 Group 18: Noble Gases Group 18: Noble Gases 4 Diatomic Molecules Diatomic Molecules

(c) 2006, Mark Rosengarten Group 1: Alkali Metals 4 Most active metals, only found in compounds in nature 4 React violently with water to form hydrogen gas and a strong base: 2 Na (s) + H 2 O (l)  2 NaOH (aq) + H 2 (g) 4 1 valence electron 4 Form +1 ion by losing that valence electron 4 Form oxides like Na 2 O, Li 2 O, K 2 O

(c) 2006, Mark Rosengarten Group 2: Alkaline Earth Metals 4 Very active metals, only found in compounds in nature 4 React strongly with water to form hydrogen gas and a base: –Ca (s) + 2 H 2 O (l)  Ca(OH) 2 (aq) + H 2 (g) 4 2 valence electrons 4 Form +2 ion by losing those valence electrons 4 Form oxides like CaO, MgO, BaO

(c) 2006, Mark Rosengarten Groups 3-11: Transition Metals 4 Many can form different possible charges of ions 4 If there is more than one ion listed, give the charge as a Roman numeral after the name 4 Cu +1 = copper (I) Cu +2 = copper (II) 4 Compounds containing these metals can be colored.

(c) 2006, Mark Rosengarten Group 17: Halogens 4 Most reactive nonmetals 4 React violently with metal atoms to form halide compounds: 2 Na + Cl 2  2 NaCl 4 Only found in compounds in nature 4 Have 7 valence electrons 4 Gain 1 valence electron from a metal to form -1 ions 4 Share 1 valence electron with another nonmetal atom to form one covalent bond.

(c) 2006, Mark Rosengarten Group 18: Noble Gases 4 Are completely nonreactive since they have eight valence electrons, making a stable octet. 4 Kr and Xe can be forced, in the laboratory, to give up some valence electrons to react with fluorine. 4 Since noble gases do not naturally bond to any other elements, one atom of noble gas is considered to be a molecule of noble gas. This is called a monatomic molecule. Ne represents an atom of Ne and a molecule of Ne.

(c) 2006, Mark Rosengarten Diatomic Molecules 4 Br, I, N, Cl, H, O and F are so reactive that they exist in a more chemically stable state when they covalently bond with another atom of their own element to make two-atom, or diatomic molecules. 4 Br 2, I 2, N 2, Cl 2, H 2, O 2 and F 2 4 The decomposition of water : 2 H 2 O  2 H 2 + O 2