Atoms, Elements, and Ions

Atoms, Elements, and Ions

The Language of Chemistry • CHEMICAL ELEMENTS - • pure substances that cannot be decomposed by ordinary means to other substances. Aluminum Bromine Sodium

Lesson 1The Atom: From Idea to Theory Essential Question • How has the theory of the atom evolved over time? Objectives • To summarize Dalton’s atomic theory. • To explain the laws that support Dalton’s atomic theory.

Electron cloud Nucleus The Atom An atom consists of a • nucleus • (of protonsand neutrons) • electrons in space about the nucleus.

The Structure of An Atom

Copper atoms on silica surface. • An atomis the smallest particle of an element that has the chemical properties of the element. Distance across = 1.8 nanometer (1.8 x 10-9 m)

History of the atom • Not the history of atom, but the idea of the atom. • Original idea began • Ancient Greece (400 B.C.) • Democritus- Greek philosopher • “father of modern science” • India (600B.C.) • Hindu Nyaya philosophy Not really sure which one.

History of Atom • Smallest possible piece? • Atomos - not to be cut • Looked at beach • Made of sand • Cut sand - smaller sand

Another Greek • Aristotle - Famous natural philosopher • Believer of the 4 earthly elements • Fire - Hot • Air - light • Earth - cool, heavy • Water – wet • Plus one of his own • Aether – divine/heavenly bodies • Blend these elements in different proportions to get all substances

Who Was Right? • Greek society was slave based. • Beneath famous to work with hands. • Did not experiment. • Greeks settled disagreements by argument. • Aristotle was more famous, so he won. • His ideas carried through middle ages. • Later, Alchemists attempted to change lead to gold.

Who’s Next? • Late 1700’s - John Dalton- from England. • Math & natural philosophy tutor- summarized results of his experiments and those of others. • Dalton’s Atomic Theory • Combined ideas of elements with that of atoms.

Dalton’s Atomic Theory • matter is composed, indivisible particles (atoms) • all atoms of a particular element are identical • different elements have different atoms • atoms combine in certain whole-number ratios • Chemical reactions involve the rearrangement of atoms. • No atoms are created, destroyed, or changed into atoms of any other elements.

Dalton’s support for his theory • Law of Conservation of Mass – Mass is neither created nor destroyed during ordinary chemical reactions. • Let’s look at an equation: • 2H2 + O2>> 2H2O • The quantity and mass of reactants equals the quantity and mass of the products.

Problems with Dalton’s Atomic Theory? 1. matter is composed, indivisible particles Atoms Can Be Divided, but only in a nuclear reaction 2. all atoms of a particular element are identical Does not Account for Isotopes (atoms of the same element but a different mass due to a different number of neutrons)! 3. different elements have different atoms YES! 4. atoms combine in certain whole-number ratios YES! Called the Law of Definite Proportions 5. In a chemical reaction, atoms are merely rearranged to form new compounds; they are not created, destroyed, or changed into atoms of any other elements. Yes, except for nuclear reactions that can change atoms of one element to a different element

Modern Atomic Theory • We know today that atoms are made of electrons, protons, neutrons. • We will study that next. • Even More Modern Atomic Theory • Known as the Standard Model • protons & neutrons are made of six different “flavors” of quarks. • Electrons are made of leptons

Plus there’s more • Fermions Baryons • Neutrinos Gluons • Higgs-Boson – the most fundamental particle • Not to mention that EVERY particle of matter has an antimatter counterpart. • But we are not studying this stuff!

Learning Check 1a • C + O2 >> ?? According to the Law of Conservation of Mass, the correct answer for the product is: • CO • C2O • CO2 • C1/2O

Learning Check 1b • Which of Dalton’s statement(s) is NO longer correct today? • All matter is composed of atoms. • Atoms of any given element are identical, and are different than atoms of another element. • Atoms cannot be created, destroyed, or subdivided. • Atoms of different elements combine in whole number ratios. • In chemical reactions, atoms are combined, separated, or rearranged. Isotopes-atoms of an element with different # neutrons Nuclear fission – splitting an atom

Learning Check 1c • Explain how an idea, an opinion, a theory, and a law all become connected? • First, someone has an idea; then persuades others to believe, which is an opinion. Skeptical people need proof. Experiments and data provide proof which creates a theory. After many, many years of experiments trying to disprove without success, a theory becomes a law.

Lesson 2Structure of the Atom Essential Question • How has scientific discovery and technology supported the structure of the atom? Objectives • To summarize the experiments that contributed to the structure of the atom. • Describe the structure of an atom including location of protons, electrons, and neutrons with respect to the nucleus. • Distinguish among protons, electrons, and neutrons in terms of relative mass and charge.

Parts of Atoms • J. J. Thomson - English physicist. (1897) • Made a piece of equipment called a cathode ray tube. • It is a vacuum tube - all the air has been pumped out.

Voltage source Thomson’s Experiment - + Vacuum tube Metal Disks

Voltage source Thomson’s Experiment - +

Voltage source Thomson’s Experiment - + • Passing an electric current makes a beam appear to move from the negative to the positive end

Voltage source Thomson’s Experiment • By adding an electric field

Voltage source Thomson’s Experiment + - • By adding an electric field

Voltage source Thomson’s Experiment + - • By adding an electric field he found that the moving pieces had a negative charge

More from Thomson • JJ Thomson third experiment confirmed that the negative charge was coming from very tiny particles (1000x smaller than hydrogen atom) and were not rays. He called them electrons. • In 1904 Thomson proposed his model of an atom. • Original knickname - Plum Pudding Model • Today’s knickname – Blueberry Muffin model (Why?)

Millikan’s Experiment (1909) • Millikan determined the size of the charge of an electron. • He put a charge on a tiny drop of oil and measured how strong an electric field had to be in order to stop the oil drop from falling.

Rutherford’s experiment • Ernest Rutherford -English physicist. (1911) • Believed in Thomson’s model of the atom (1904). • Wanted to see how big they are. • Used radioactivity. • Alpha particles - positively charged pieces- helium atoms minus electrons • Shot them at gold foil which can be made a few atoms thick.

Rutherford’s experiment • When an alpha particle hits a fluorescent screen, it glows. • Here’s what it looked like

Fluorescent Screen Lead block Uranium Gold Foil

He Expected • The alpha particles to pass through without changing direction very much. • Because…? • …the positive charges were thought to be spread out evenly. Alone they were not enough to stop the alpha particles.

What he expected

Because

He thought the mass was evenly distributed in the atom

Since he thought the mass was evenly distributed in the atom

What he got

+ How he explained it • Atom is mostly empty. • Small dense, positive piece at center. • Alpha particles are deflected by it if they get close enough.

Density & the AtomConclusion • Since most of the particles went through, it was mostly empty space. • Because the pieces turned so much, the positive pieces were heavy. • Small volume, big mass, big density. • This small dense positive area is the nucleus.

Atoms, Elements, and Ions