Dalton’s Atomic Theory Law of conservation of mass Law of multiple proportions

Law of Conservation of Mass Figure 2.5 | A representation of combining gases at the molecular level. The spheres represent atoms in the molecules. Law of Conservation of Mass LLa Figure 2-5 p50

Dalton’s Atomic Theory Law of Multiple Proportions 2 Law of Multiple Proportions

The Structure of the Atom Dalton’s atomic theory atom, the basic unit of element However, atom has subatomic particles -Electrons, neutrons, protons Electrons -negative charge -negligible mass Dalton imagined an atom that was both extremely small and indivisible. But later in the 19th century and the beginning of the 20th century, study of subatomic particles were done and three such particles-electrons, protons, and neutrons were discovered. Discovery of electron: Cathode ray tube, cathode (-)and anode (+) connected to high voltage. Cathode emits an invisible ray drawn to anode and strikes a specially coated surface producing fluorescence. Reacted different ways with magenetic and electric fields. Finally figured out this to be negatively charged particle called electron. J.J. Thompson and Millikan found the charge and mass of an electron. Next slide shows the size of atom and nucleus. Atoms are relatively “fuzzy” do not have well defined boundaries. H – 1 proton ,mass 1 He-2protons, mass 4, should be 2. Led to the discovery of neutrons H has no neutrons-the only one element like that. He has 2 neutrons, almost the same mass as neutrons, so total mass is 4.

The Structure of the Atom (cont.) Atom is neutral Nucleus-a dense central core of the atom Protons -positive charge mass is 1840 times the mass of electron Neutrons -electrically neutral - Mass almost the same as proton Atoms are electrically neutral, so it needs a +ve charge particle in equal number. Later Rutherford use alpha particles to probe the structure of atoms.

Atomic Number, Mass Number, and Isotopes Atomic number (Z) = number of protons in a neutral atom #protons = # of electrons (in a neutral atom) Mass number (A) = number of protons (Z) + number of neutrons Number of neutrons = A-Z Chemical identity solely depend on the atomic number. For example, in the universe every atom which contains 9 protons is Fluorine. Show the periodic Table and ask about different elements. Atomic number is the number on the top of the element. In the periodic Table, it is the atomic weight, average of the mass of different isotopes. Ask different elements in the periodic table –No. of protons, neutrons, and electrons.

Ernest Rutherford (1911) Explained the nuclear atom. The atom has a dense center of positive charge called the nucleus. Electrons travel around the nucleus at a large distance relative to the nucleus. Copyright © Cengage Learning. All rights reserved

(1908 Nobel Prize in Chemistry) Rutherford’s Experiment (1908 Nobel Prize in Chemistry) Rutherford’s alpha scattering expt: Alpha particles (positive) went through thin foils of gold.- undeflected, slightly deflected, deflected, and bounced back. (+) charge is concentrated in the nucleus, which is a dense central core within the atom. Most of the atom must have empty space. This explain all the different types of deflection. particle velocity ~ 1.4 x 107 m/s (~5% speed of light) atoms positive charge is concentrated in the nucleus proton (p) has opposite (+) charge of electron (-) mass of p is 1840 x mass of e- (1.67 x 10-24 g)

Cathode-Ray Tube (J.J. Thompson) Discovery of electron and Millikan with oil drop experiment determined the charge/mass of an electron (negligible) M Copyright © Cengage Learning. All rights reserved

Three types of radioactive emission exist: Henri Becquerel (1896) Discovered radioactivity by observing the spontaneous emission of radiation by uranium. Three types of radioactive emission exist: Gamma rays (ϒ) – high energy light Beta particles (β) – a high speed electron Alpha particles (α) – a particle with a 2+ charge Copyright © Cengage Learning. All rights reserved

Radioactivity is spontaneous emission of particles and /or radiation Radioactivity is spontaneous emission of particles and /or radiation. Marie Curie, Rontgen, Becquerrel are involved in the discovery. You can see all these names in the radioactive units. Alpha, +ve. Like He atom equivalen t to 2 protons, deflected by +vely charged particle Beta, -ve, like electron, deflected by negativecharge Gamma, no charge, penetreates through matter Radioactivity is spontaneous emission of particles and /or radiation

Small compared with the overall size of the atom. The nucleus is: Small compared with the overall size of the atom. Extremely dense; accounts for almost all of the atom’s mass. Copyright © Cengage Learning. All rights reserved

Nuclear Atom Viewed in Cross Section Copyright © Cengage Learning. All rights reserved

In nature most elements contain mixtures of isotopes. Atoms with the same number of protons but different numbers of neutrons. Show almost identical chemical properties; chemistry of atom is due to its electrons. In nature most elements contain mixtures of isotopes. Copyright © Cengage Learning. All rights reserved

Two Isotopes of Sodium Copyright © Cengage Learning. All rights reserved

Isotopes are identified by: Atomic Number (Z) – number of protons Mass Number (A) – number of protons plus number of neutrons Copyright © Cengage Learning. All rights reserved

A certain isotope X contains 23 protons and 28 neutrons. EXERCISE! A certain isotope X contains 23 protons and 28 neutrons. What is the mass number of this isotope? Identify the element. Mass Number = 51 Vanadium The mass number is 51. Mass Number = # protons + # neutrons. Mass Number = 23 + 28 = 51. The element is vanadium. Copyright © Cengage Learning. All rights reserved

Chemical Bonds Covalent Bonds Bonds form between atoms by sharing electrons. Resulting collection of atoms is called a molecule. Copyright © Cengage Learning. All rights reserved

Covalent Bonding To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE Copyright © Cengage Learning. All rights reserved

Chemical Bonds Ionic Bonds Bonds form due to force of attraction between oppositely charged ions. Ion – atom or group of atoms that has a net positive or negative charge. Cation – positive ion; lost electron(s). Anion – negative ion; gained electron(s). Copyright © Cengage Learning. All rights reserved

Molecular vs Ionic Compounds To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE Copyright © Cengage Learning. All rights reserved

A certain isotope X+ contains 54 electrons and 78 neutrons. EXERCISE! A certain isotope X+ contains 54 electrons and 78 neutrons. What is the mass number of this isotope? 133 The mass number is 133. The plus charge in X+ means that the ion has lost an electron, therefore the number of protons is 55 (54+1). The ion is Cs+ with a mass number of 133 (55+78). Note: Use the red box animation to assist in explaining how to solve the problem. Copyright © Cengage Learning. All rights reserved

CONCEPT CHECK! Which of the following statements regarding Dalton’s atomic theory are still believed to be true? Elements are made of tiny particles called atoms. All atoms of a given element are identical. – (due to Isotopes) A given compound always has the same relative numbers and types of atoms. IV. Atoms are indestructible. –(nuclear chemistry) Statements I and III are true. Statement II is not true (due to isotopes and ions). Statement IV is not true (due to nuclear chemistry). Copyright © Cengage Learning. All rights reserved

The Periodic Table Metals vs. Nonmetals Groups or Families – elements in the same vertical columns; have similar chemical properties Periods – horizontal rows of elements Copyright © Cengage Learning. All rights reserved

The Periodic Table

Alkaline Earth Metals (2A) Groups or Families Table of common charges formed when creating ionic compounds. Group or Family Charge Alkali Metals (1A) 1+ Alkaline Earth Metals (2A) 2+ Halogens (7A) 1– Noble Gases (8A) Copyright © Cengage Learning. All rights reserved

Naming Compounds Binary Compounds Composed of two elements Ionic and covalent compounds included Binary Ionic Compounds Metal—nonmetal Binary Covalent Compounds Nonmetal—nonmetal Copyright © Cengage Learning. All rights reserved

Binary Ionic Compounds (Type I) 1. The cation is always named first and the anion second. 2. A monatomic cation takes its name from the name of the parent element. 3. A monatomic anion is named by taking the root of the element name and adding –ide. Copyright © Cengage Learning. All rights reserved

Binary Ionic Compounds (Type I) Examples: KCl Potassium chloride MgBr2 Magnesium bromide CaO Calcium oxide Copyright © Cengage Learning. All rights reserved

Binary Ionic Compounds (Type II) Metals in these compounds form more than one type of positive ion. Charge on the metal ion must be specified. Roman numeral indicates the charge of the metal cation. Transition metal cations usually require a Roman numeral. Elements that form only one cation do not need to be identified by a roman numeral. Copyright © Cengage Learning. All rights reserved

Binary Ionic Compounds (Type II) Examples: CuBr Copper(I) bromide FeS Iron(II) sulfide PbO2 Lead(IV) oxide Copyright © Cengage Learning. All rights reserved

Polyatomic Ions Must be memorized (see Table 2.5 on pg. 65 in text). Examples of compounds containing polyatomic ions: NaOH Sodium hydroxide Mg(NO3)2 Magnesium nitrate (NH4)2SO4 Ammonium sulfate Copyright © Cengage Learning. All rights reserved

Formation of Ionic Compounds To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE Copyright © Cengage Learning. All rights reserved

Binary Covalent Compounds (Type III) Formed between two nonmetals. 1. The first element in the formula is named first, using the full element name. 2. The second element is named as if it were an anion. 3. Prefixes are used to denote the numbers of atoms present. 4. The prefix mono- is never used for naming the first element. Copyright © Cengage Learning. All rights reserved

Prefixes Used to Indicate Number in Chemical Names Copyright © Cengage Learning. All rights reserved

Binary Covalent Compounds (Type III) Examples: CO2 Carbon dioxide SF6 Sulfur hexafluoride N2O4 Dinitrogen tetroxide Copyright © Cengage Learning. All rights reserved

Flowchart for Naming Binary Compounds Copyright © Cengage Learning. All rights reserved

Overall Strategy for Naming Chemical Compounds Copyright © Cengage Learning. All rights reserved

Acids Acids can be recognized by the hydrogen that appears first in the formula—HCl. Molecule with one or more H+ ions attached to an anion. Copyright © Cengage Learning. All rights reserved

Acids If the anion does not contain oxygen, the acid is named with the prefix hydro– and the suffix –ic. Examples: HCl Hydrochloric acid HCN Hydrocyanic acid H2S Hydrosulfuric acid Copyright © Cengage Learning. All rights reserved

Acids If the anion does contain oxygen: The suffix –ic is added to the root name if the anion name ends in –ate. Examples: HNO3 Nitric acid H2SO4 Sulfuric acid HC2H3O2 Acetic acid Copyright © Cengage Learning. All rights reserved

Acids If the anion does contain oxygen: The suffix –ous is added to the root name if the anion name ends in –ite. Examples: HNO2 Nitrous acid H2SO3 Sulfurous acid HClO2 Chlorous acid Copyright © Cengage Learning. All rights reserved

Flowchart for Naming Acids Copyright © Cengage Learning. All rights reserved

Which of the following compounds is named incorrectly? EXERCISE! Which of the following compounds is named incorrectly? KNO3 potassium nitrate TiO2 titanium(II) oxide Sn(OH)4 tin(IV) hydroxide PBr5 phosphorus pentabromide CaCrO4 calcium chromate Ti charge should be 4. titanium (IV) oxide The correct answer is “b”. The charge on oxygen is 2-. Since there are two oxygen atoms, the overall charge is 4-. Therefore, the charge on titanium must be 4+ (not 2+ as the Roman numeral indicates). Copyright © Cengage Learning. All rights reserved