Warm Up 9/17/12. How long have people been interested in understanding matter and its structure? A. Thousands of years. B.

Transcription

1 Warm Up 9/17/12 How long have people been interested in understanding matter and its structure? A. Thousands of years B. Hundreds of years C. A few years D. Never

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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 Ancient Philosophy Who: Aristotle, Democritus When: More than 2000 years ago Where: Greece What: Aristotle believed in 4 elements: Earth, Air, Fire, and Water. Democritus believed that matter was made of small particles that could not be divided. He named them atoms from atomos meaning uncut or indivisible. He thought different kinds of atoms had different properties. Why: Aristotle and Democritus used observation and inference to explain the existence of everything.

5 Aristotle Democritus

6 Alchemists Who: European Scientists When: 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 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.

9 John Dalton The 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.

10 John Dalton

11 Discovery of Electrons Who: J. J. Thomson 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.

12 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.

13 J. J. Thompson

14 Atomic Structure I Who: Ernest Rutherford When: 1911 Where: England, New Zealand 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.

15 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. emistry/flash/ruther14.swf

16 Ernest Rutherford

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

18 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.

19 Niels Bohr

20 Modern Model/Wave Model Shrodinger 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.

21 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.

22 Electron Cloud Model

23 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. Energy Level Number of Orbitals Maximum Number of Electrons 1 (s) (s, p) (s p d) (s p d f) 16 32

24 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:

25 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.

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27 Classes of Elements Metal-left of stair step Nonmetal-right of stair step Metalloid- touching stair step

28 Metals Solids (except Hg) Good conductors of heat and electricity Malleable- can be hammered into sheets Ductile- can be drawn into wires Have luster (shiny)

29 Nonmetals Brittle solids (will shatter if hit with a hammer) or gases (b/c low boiling points) Poor conductors of heat and electricity

30 Metalloid Have some properties of metals and some of nonmetals. Si and Ge are good insulators at low temperatures, but good conductors at high temperatures. Semiconductors used in computer chips.

31 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.

32 Families Alkali Metals Alkaline Earth Metals Transition Metals Boron Group Carbon Group Nitrogen Group Oxygen Group Halogens Noble Gases

33 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

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

35 The Boron and Carbon Families Boron Group 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.

36 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.