Atoms: The Building Blocks of Matter Chapter 3 Table of Contents Section 1The Atom: From Philosophical Idea to Scientific Theory Section 2The Structure of the Atom Section 3Counting Atoms
Foundations of Atomic Theory Greeks- Democritus - atomos- “indivisible” Ideas based on opinion/thoughts Section 1 The Atom: From Philosophical Idea to Scientific Theory Chapter 3
Foundations of Atomic Theory 1790’s- quantitative analysis of chemical reactions Several Laws that resulted from experimentation: Law of Conservation of Mass Law of Definite Proportions Law of Multiple Proportions
Section 1 The Atom: From Philosophical Idea to Scientific Theory Chapter 3 Law of Conservation of Mass- mass is neither created nor destroyed in ordinary chemical reactions.
Law of Definite Proportions A chemical compound always has the same mass ratio of elements Example: SiO2 silicon dioxide (sand) 46.74% silicon 53.26 % oxygen Mass of desired element X 100 Total mass of compound
Section 1 The Atom: From Philosophical Idea to Scientific Theory Chapter 3 Law of multiple proportions: The same two elements may combine in different whole number ratios- will give two different compounds
Dalton’s Atomic Theory 1808- based on experimental work- 1. All matter is composed of extremely small particles called atoms. 2. Atoms of a given element are identical. 3. Atoms cannot be subdivided, created, or destroyed. 4. Atoms of different elements combine in simple whole-number ratios to form chemical compounds. 5. In chemical reactions, atoms are combined, separated, or rearranged. Section 1 The Atom: From Philosophical Idea to Scientific Theory Chapter 3
Modern Atomic Theory Not all aspects of Dalton’s atomic theory have proven to be correct. We now know that: Section 1 The Atom: From Philosophical Idea to Scientific Theory Chapter 3 • Atoms are divisible into even smaller particles • A given element can have atoms with different masses.--- isotopes
The Structure of the Atom An atom is the smallest particle of an element that retains the chemical properties of that element. Section 2 The Structure of the Atom Chapter 3
The Structure of the Atom • Electrons- found by JJ Thomson (1897) • Used cathode ray tube • Negatively charged particles • Mass is small 1/1837 mass of hydrogen atom • Relative mass 0 amu (atomic mass unit)
Cathode ray tube Section 2 The Structure of the Atom Chapter 3
Discovery of the Electron- J. J. Thomson Cathode Rays and Electrons Section 2 The Structure of the Atom Chapter 3 • Experiments in the late 1800s showed that cathode rays were composed of negatively charged particles. • These particles were named electrons. • “Plum-pudding” model- think chocolate chip cookie
The Structure of the Atom • Protons- found by Ernest Rutherford(1918) • positively charged particles found in nucleus • Relative mass 1 amu (atomic mass unit) • # of protons- identifies element
The Structure of the Atom • Neutrons- found by James Chadwick(1932) • neutral charge • particle found in nucleus • Relative mass 1 amu (atomic mass unit)
Section 2 The Structure of the Atom Chapter 3 Properties of Subatomic Particles
Discovery of the Atomic Nucleus More detail of the atom’s structure was provided in 1911 by Ernest Rutherford and his associates Hans Geiger and Ernest Marsden. The results of their gold foil experiment led to the understanding that the atom is mostly empty space with a small, dense, positive region. Rutherford called this positive bundle of matter the nucleus. Section 2 The Structure of the Atom Chapter 3
Section 2 The Structure of the Atom Chapter 3 Gold Foil Experiment
Section 2 The Structure of the Atom Chapter 3 Gold Foil Experiment on the Atomic Level
Atomic Models- Visual Overview Dalton Thomson Rutherford Today?????
Determining the components of an atom • Use the periodic table and given information in symbolic form to determine: • Atomic number • Mass number • Numbers of protons, neutrons and electrons • Charge of an ion
Symbol you will see to represent an element AX Z A – mass number Z – atomic number X- symbol of the element
Atomic Number Atoms of the same element all have the same number of protons. Theatomic number(Z) of an element is the number of protons of each atom of that element. Section 3 Counting Atoms Chapter 3
Visual Concepts Chapter 3 Atomic Number
Mass Number The mass number is the total number of protons and neutrons that make up the nucleus of an isotope. Section 3 Counting Atoms Chapter 3
Visual Concepts Chapter 3 Mass Number
Isotopes Isotopes are atoms of the same element that have different masses. The isotopes of a particular element all have the same number of protons and electrons but different numbers of neutrons. Most of the elements consist of mixtures of isotopes. Section 3 Counting Atoms Chapter 3
Designating Isotopes Hyphen notation: The mass number is written with a hyphen after the name of the element. uranium-235 Nuclear symbol: The superscript indicates the mass number and the subscript indicates the atomic number. Section 3 Counting Atoms Chapter 3
Sample Problem A How many protons, electrons, and neutrons are there in an atom of chlorine-37? Section 3 Counting Atoms Chapter 3
Additional Problems Xe-135 ? p ? n ? e 25Mg +2 ? P ? N ? e Section 3 Counting Atoms Chapter 3
Relative Atomic Masses The standard used to compare units of atomic mass is the carbon-12 atom, which has been arbitrarily assigned a mass of exactly 12 atomic mass units, or 12 amu. One atomic mass unit,or 1 amu, is exactly 1/12 the mass of a carbon-12 atom. The atomic mass of any atom is determined by comparing it with the mass of the carbon-12 atom. Section 3 Counting Atoms Chapter 3
Average Atomic Masses of Elements Average atomic mass is the weighted average of the atomic masses of the naturally occurring isotopes of an element. Calculating Average Atomic Mass The average atomic mass of an element depends on both the mass and the relative abundance of each of the element’s isotopes. Section 3 Counting Atoms Chapter 3
Mass Spectrometer- http://www.chemguide.co.uk/analysis/masspec/masspec.GIF www.alevelchemistry.co.uk/Quizzes/images/mass_spectrometry
Average Atomic Masses of Elements, continued Calculating Average Atomic Mass, continued Section 3 Counting Atoms Chapter 3 • Copper consists of 69.15% copper-63, which has an atomic mass of 62.929 601 amu, and 30.85% copper-65, which has an atomic mass of 64.927 794 amu.
Relating Mass to Numbers of Atoms The Mole- “The Chemist’s Dozen” Section 3 Counting Atoms Chapter 3 • SI unit to describe quantity. • mole (abbreviated mol) • Enables small particles to be counted Avogadro’s Number • Avogadro’s number 6.02 1023 • number of particles in exactly one mole of a pure substance.
Relating Mass to Numbers of Atoms, continued Molar Mass Section 3 Counting Atoms Chapter 3 • The mass of one mole of a pure substance is called the molar mass of that substance. • Molar mass is usually written in units of g/mol. • The molar mass of an element is numerically equal to the atomic mass of the element
Relating Mass to Numbers of Atoms, continued Chemists use molar mass as a conversion factor in chemical calculations. Section 3 Counting Atoms Chapter 3 Gram/Mole Conversions • For example, the molar mass of helium is 4.00 g He or 1 mol He 1 mol He 4.00 g He
Mole conversions Molar mass in grams = 1 MOLE = 6.02 X1023 particles Samples to try moles and grams moles and atoms atoms and grams
Sample Problems- Moles to grams What is the mass of one mole of aluminum? What is the mass of 1 mol of chlorine? Section 3 Counting Atoms Chapter 3
Sample Problem – What is the mass of .455 moles of silver? What is the mass of 2.50 X 10-4 moles of lead? Section 3 Counting Atoms Chapter 3
Sample Problem- Moles to atoms How many atoms are in 3.45 moles of copper? Section 3 Counting Atoms Chapter 3
Moles to grams • How much lead should I mass to get 1.67 moles?
Atoms to moles How many moles of aluminum do you have with 4.75 1034 atoms of aluminum? Section 3 Counting Atoms Chapter 3
Atoms to grams • If I wanted 5.00 X 1015 atoms of gold, how many grams would I need?