Dalton s s Atomic Theory

Transcription

1 Dalton s s Atomic Theory 1. Elements are made of tiny particles called atoms. 2. All atoms of a given element are identical (not exactly; isotopes) 3. The atoms of a given element are different from those of any other element. 4. Atoms of one element can combine with atoms of other elements to form compounds. A given compound always has the same relative numbers and types of atoms. 5. Atoms are indivisible in chemical processes. That is, atoms are not created or destroyed in chemical reactions. A chemical reaction simply changes the way the atoms are grouped together.

2 Laws of Chemical Combination Law of Definite Proportions: : Different samples of the same compound always contain its constituent elements in the same proportions by mass This is also called the Law of Constant Composition Suppose we analyze samples of water from different sources We will find in each sample the same ratio by mass of hydrogen to t oxygen.

3 So A 10.0 gram sample of water, H 2 O, is comprised of 8.9 grams oxygen and 1.1 grams hydrogen. Thus, a gram sample of water, is comprised of 89.0 grams of oxygen and 11.0 grams of hydrogen.

4 Laws of Chemical Combination Law of Multiple Proportions (or, Dalton s s Law): : If two elements can combine to form more than one compound, then the masses of one element that combine with a fixed mass of the other element are in the ratios of small whole numbers For instance, the atom carbon forms two stable compounds with the atom oxygen: Carbon Monoxide (C 1 O 1 ) and Carbon Dioxide (C 1 O 2 ) Neither C 1.2 O 1.3 nor C 1.2 O 2.2, respectively

5 The Structure of the Atom Atom: : The basic unit of an element that can enter into chemical combination. They are made of even smaller particles called subatomic particles. Electrons Protons Neutrons

6 Summary of the Structure of the Atom Mass and Charge of Subatomic Particles Particle Mass (grams) Electron x Charge 28-1 Proton x Neutron x

7 Isotopes Let us modify Dalton s s Atomic Theory. Isotopes: : Atoms having the same atomic number but different mass numbers. Atomic Number: : The number of protons in the nucleus of an atom. Mass Number: : The total number of neutrons and protons present in the nucleus of an atom.

8 Isotopes We use the symbol to represent the isotope. Where X = the symbol of the element A = the mass number Z = the atomic number How do we calculate the number of neutrons? Mass Number = Number of Protons + Number of Neutrons Number of neutrons = A - Z

9 Isotopes Example Give the number of protons, neutrons, and electrons in Strontium-90. Example Give the number of protons, neutrons, and electrons in Mercury-201. Example Give the symbol for the phosphorous atom that contains 17 neutrons.

10 The mole Mole = amt that contains as many things as there are atoms of 12 g of C-C 12 1 mole = x particles Molar mass (MM) = mass in grams per 1 mole of particle (g/mol)

11 Introduction to the Periodic Table

12 How to interpret the PT Why the symbols? Why the numbers? Why the columns? Why the rows?

13 Introduction to the Periodic Table Groups: : The elements in a vertical column of the periodic table. Period: : The elements in each horizontal row of the periodic table. Alkali Metals: : The Group 1A elements (Li,Na,K,Rb,Cs,Fr( Li,Na,K,Rb,Cs,Fr). Alkaline Earth Metals: : The Group 2A elements (Be,Mg,Ca,Sr,Ba,Ra). Halogens: : The nonmetallic elements in Group 7A (F,Cl,Br,I,At). Noble Gases: : The nonmetallic elements in Group 8A (He,Ne,Ar,Kr,Xe,Rn). Transition Metals: : Group of elements in the middle of the periodic table.

14 Introduction to the Periodic Table Elements can be divided into 3 categories: Metals, Nonmetals, Metalloids Metal: : Good Conductor of heat and electricity. Physical Properties of Metals 1. Efficient conduction of heat and electricity 2. Malleability (they can be hammered into thin sheets) 3. Ductility (they can be pulled into wires) 4. A lustrous (shiny) appearance Example Lithium, Magnesium, Chromium, Gold, and many others.

15 Introduction to the Periodic Table Nonmetals: : Usually a poor conductor of heat and electricity, and it has more varied physical properties than a metal. They appear in the upper right-hand hand corner of the periodic table. Example Nitrogen, Oxygen, Bromine, Carbon, Phosphorous, Sulfur, and many others Metalloids: : or Semimetals have properties that fall between those of metals and nonmetals Example Boron, Silicon, Germanium, Arsenic, Antimony, Tellurium, Polonium, Astatine

16 Introduction to the Periodic Table Give the symbol and atomic number for each of the elements. Determine whether the element is a metal or a nonmetal. Also, determine what family it belongs to. (a) Argon (b) Chlorine (c) Barium (d) Cesium

17 Natural States of the Elements Noble Metals: Unreactive metals (Au, Ag, Pt). Noble Gases: : The nonmetallic elements in Group 8A (He, Ne, Ar,, Kr, Xe, Rn). Diatomic Molecule: : A molecule that consists of two atoms (N 2, O 2, H 2, F 2, Cl 2, Br 2, I 2 ). The diatomic molecules (H 2,N 2,O 2,F 2,Cl 2 ) are gaseous in their elemental forms at normal temperatures. Br 2 and Hg are liquids in their elemental forms at normal temperatures.

18 Natural States of the Elements Allotropes: : Two or more forms of the same element that differ significantly in chemical and physical properties. Example Diamond, Graphite, Buckyball