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Warm Up 10/19/12

Warm Up 10/19/12. How long have people been interested in understanding matter and its structure? Thousands of years Hundreds of years A few years Never. History of Atomic Structure. What is an atom?. The smallest particle of an element.

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Warm Up 10/19/12

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  1. Warm Up10/19/12 How long have people been interested in understanding matter and its structure? • Thousands of years • Hundreds of years • A few years • Never

  2. History of Atomic Structure

  3. What is an atom? • The smallest particle of an element. • Atoms are so small that we cannot even see them with a microscope. • How do scientists know what they look like or how they are made?

  4. Democritus Aristotle http://www.youtube.com/watch?v=lY-Thmrt1Ts

  5. Ancient Philosophy • Who:Aristotle, Democritus • When:More than 2000 years ago • Where:Greece • What: • Aristotlebelieved in 4 elements: Earth, Air, Fire, and Water. • Democritusbelieved that matter was made of small particles that could not be divided. He named them “atoms” meaning uncut or indivisible. • Why:Aristotle and Democritus used observation and inference to explain the existence of everything.

  6. Alchemists • Who:European Scientists • When:800 – 900 years ago • Where:Europe • What:Their work developed into what is now modern chemistry. • Why:Trying to change ordinary materials into gold.

  7. Alchemic Symbols

  8. Becquerel and Curie • Henri Becquerel—(1896)-- While studying the effect of x-rays on photographic film, he discovered some chemicals spontaneously decompose and give off very penetrating rays.  • Marie Curie—(1898)--Studied uranium and thorium and called their spontaneous decay process "radioactivity". She and her husband Pierre also discovered the radioactive elements polonium and radium.

  9. Lavoisier— elements combine to form compounds. • Proust—Law of Definite Proportions • The mass of elements of reactants equals the mass of elements of products.

  10. Particle Theory • Who:John Dalton • When:1808 • Where:England • What: Described atoms as tiny particles that could not be divided. Thought each element was made of its own kind of atom. • Why:Building on the ideas of Democritus in ancient Greece.

  11. John DaltonThe Atomic Theory • All elements are composed of atoms. • All atoms of the same element are the same, but different from other elements. They have same size, mass and properties. • Compounds contain atoms of more than one element, combined in whole number ratios. • Compounds form when atoms join, separate, or rearrange.

  12. John Dalton

  13. Discovery of Electrons • Who:J. J. Thompson • When:1897 • Where:England • What:Thompson discovered that electrons were smaller particles of an atom and were negatively charged. • Why:Thompson knew atoms were neutrally charged, but couldn’t find the positive particle.

  14. J. J. Thomson • First to show atoms are made of subatomic particles. • Plum pudding model or chocolate chip ice cream model. Pudding or ice cream is positive charged mass o f matter and plums or chocolate chips are the negative charges evenly scattered throughout the atom. • Used an electric current and the cathode ray tube to learn more about atoms.

  15. J. J. Thompson

  16. Atomic Structure I • Who:Ernest Rutherford • When:1911 • Where:England • What:Conducted an experiment to isolate the positive particles in an atom. Decided that the atoms were mostly empty space, but had a dense central core. • Why:He knew that atoms had positive and negative particles, but could not decide how they were arranged.

  17. Rutherford • The atom is mostly empty space. • All of the positive charge is located in the center of the atom in the nucleus. • Electrons move randomly in the space around the nucleus. • Used the gold foil experiment. • http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14.swf

  18. Ernest Rutherford

  19. Chadwick • Protons and neutrons in nucleus. • Protons –positive • Neutrons-neutral • Electrons-negative • Proton mass = neutron mass; electrons much smaller

  20. Atomic Structure II • Who:Niels Bohr • When:1913 • Where:England • What:Proposed that electrons traveled in fixed paths around the nucleus. Scientists still use the Bohr model to show the number of electrons in each orbit around the nucleus. (energy levels) • Why:Bohr was trying to show why the negative electrons were not sucked into the nucleus of the atom.

  21. Niels Bohr

  22. Modern Model/Wave ModelShrodinger—Electron Cloud Model • Uses mathematical model to describe the certainty of finding an electron at a certain location on the electron cloud. • The electron cloud is a visual model of the most likely locations for the electrons. Where the cloud is denser, there is more probability of finding an electron. • An electron can move from one energy level to another when the atom gains or loses energy.

  23. Electron Cloud Model • Electrons travel around the nucleus in random orbits. • Scientists cannot predict where they will be at any given moment. • Electrons travel so fast, they appear to form a “cloud” around the nucleus.

  24. Electron Cloud Model

  25. http://www.youtube.com/watch?v=wJ2e-uPmdYg • Atomic Theory Song: http://www.youtube.com/watch?v=vUzTQWn-wfE

  26. Atomic Orbitals • An orbital is a region of space around the nucleus where an electron is likely to be found. • An electron cloud is a good approximation of how electrons behave in their orbitals. • Each orbital can contain 2 electrons.

  27. Isotopes • Isotopes can be shown in several ways. • Symbol-Atomic Mass • H-1 (P=__, E=__, N=__) • H-2 (P=__, E=__, N=__) • H-3 (P=__, E=__, N=__) • It can also be shown:

  28. History of the Periodic Table • Mendeleev- Father of the Periodic Table; Arranged table according to increasing mass. • Moseley- Improved the table by arranging it according to atomic number (number of protons). There are a few places on the chart where the mass decreases. • Seaborg-pulled out the f block.

  29. Arrangement of the Periodic Table • Elements are arranged by atomic number (number of protons). • Each row on the periodic table is a period. • Each column on the periodic table is a group. • Similar electron configurations. • Similar chemical properties.

  30. Classes of Elements • There are many different ways to classify elements. • State of matter • Solids—black symbol • Liquid—blue symbol • Gas—red symbol • Occurrence in nature • Elements that do not occur naturally—white symbol • General properties • Metal • Nonmetal • Metalloid

  31. Metals • The majority of the elements on the periodic table. • Solids (except Hg) • Good conductors of heat and electricity • Malleable- can be hammered into sheets • Ductile- can be drawn into wires • Have luster (shiny) • Found to the left of the stairstep.

  32. Transition Metals • Metals in groups 3-12. • Form a bridge between the elements on the left and right sides of the table. • Among the first discovered (Au, Ag, Cu) • They form compounds with distinctive colors.

  33. Nonmetals • Generally have properties opposite of metals. • Poor conductors of heat and electricity. • Nonmetals have low boiling points—many nonmetals are gases at room temperature. • Brittle solids (will shatter if hit with a hammer) or gases (b/c low boiling points)

  34. Metalloid • Located between metals and nonmetals---touch the stairstep. • Have some properties of metals and some of nonmetals. • A metalloid’s ability to conduct electric current varies with temperature. • Si and Ge are good insulators at low temperatures, but good conductors at high temperatures. • Semiconductors—used in computer chips.

  35. As you move across the period, from left to right, the elements become less metallic and more nonmetallic in their properties. • Elements in a group have similar properties because they have the same number of valence electrons. They won’t be identical because they have different number of energy levels.

  36. Families • Alkali Metals • Alkaline Earth Metals • Transition Metals • Boron Group • Carbon Group • Nitrogen Group • Oxygen Group • Halogens • Noble Gases

  37. Alkali Metals • They have one outer (valence) electrons so they are very reactive. • They are only found as compounds in nature—because they are so reactive. • Reactivity increases as you move down the group. • Ex. Sodium • Stored under oil b/c so reactive • Makes NaCl • Video or Na reactivity

  38. Alkaline Earth Metals • Have 2 valence electrons. • Mg, Ca, Be

  39. The Boron and Carbon Families • Boron • Aluminum is the most abundant metal in the Earth’s crust. • Bauxite is made from Al and O. • Carbon Group • Except for water, most of the compounds in your body contain carbon. • Si is second most abundant element in Earth’s crust.

  40. Nitrogen group—N and P in fertilizer • Oxygen group—O most abundant element in Earth’s crust. • Halogens—They all have similar chemical properties.. Very, very reactive. • Noble gases- colorless, odorless, and extremely unreactive.

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