Section A1: Physical Properties

1. Section A1: Physical Properties We characterize atoms or matter according to a couple of different properties • Physical Property: A characteristic we can measure without changing the substance under examination • eg: Temperature, mass, density, melting point • Chemical Property: The ability of a substance to change into another substance • eg: Hydrogen gas has the chemical property of reacting with oxygen to make water

2. Physical Properties • When we measure a physical property, we report the results in a standardized format • SI (Systeme Internacional) units will always be used in this class • Let’s look at the Physical Property: Mass

3. Mass • A lump of iron has a mass of 15 kg • Originally, a gram was defined as: “The absolute weight of pure water equal to the cube of the hundredth pat of a meter and at the temperature of melting ice (4° C)” • Hmmm. That’s not very handy.

4. Mass • It is now defined as on thousandth of a kilogram (the SI unit of mass) • In Sevres, France, there is a block of platinum/iridium alloy that is the standard mass of 1 kilogram • All other 1kg blocks in the world come from this mass template.

5. SI Units and the Metric System You must memorize these!

6. Working with units • DO NOT GET CARELESS…EVER! • Always keep track of your units • I will take points off of anything you give me if you leave the units off • I will stare at you when you give me an answer without units until you put them in your answer • IT REALLY IS THAT IMPORTANT!!!!

7. Dimensional Analysis • You will frequently have to convert between units during your life (Yes, your entire life!) • To do this, we will need to employ DIMENSIONAL ANALYSIS • Step 1: What do you have? What do you need? • Step 2: What is the conversion factor? • Step 3: Setup a calculation that cancels your given units and puts your target units on top.

8. Dimensional Analysis: Example • How many centimeters are in 29 inches? 

9. Dimensional Analysis: Example • How many ounces are in 750 kg? 

10. Dimensional Analysis: Example • A sample of an alloy has a density of 7.9 kg/cm3. What is the density in kg/m3? 

11. Properties dependent upon the mass of the sample • Intensive property: A property that is independent of the mass of the sample • Extensive property: A property that depends in the mass of the sample. Temperature is an ________ property Volume is an ________ property

12. Density • The density of a sample is an intensive property that is calculated by dividing on extensive property (mass) by another extensive property (volume)

13. What does density really tell us? • How tightly packed the atoms are in a given space. 

14. Significant Figures • Simple rule for my class: Take the value with the lowest number of significant figures and report your answer that way. • See the rules in Appendix 1C of your text. • I won’t kill you on this (but I might just hurt you a little bit)

15. Accuracy and Precision

16. A.2: Force • Force is defined as an influence that changes the state of motion of an object • Newton’s Second Law: • An object experiencing a force undergoes an acceleration Force  acceleration F  a • The proportionality constant is mass

17. Force and Acceleration • You flick a marble with your finger. What happens? • You flick a bowling ball with your finger. What happens?

18. A.3: Energy • Energy is the key to everything: Shape, motion, chemical reactions, color, sound • But what is it really? • We will define energy as the capacity to do work. • Work is defined as motion against an opposing force

19. Energy: Examples • Energy is required to lift a book from the floor • Energy is required to move electrons through a wire • Energy is required for your cells to import glucose (to make more energy!)

20. The SI unit of energy is the joule (J) Defined as “the work done by a 1 Newton force in moving an object 1 meter” A Newton is defined as "the force necessary to accelerate a 1 kg object at 1 meter per second per second” Multiplying the Force times the distance it is exerted (1 m) gives the units of a Joule as kg m2/s2

21. Types of energy • There are three types of energy: • Kinetic energy: Energy associated with motion • Potential Energy: Energy related to position • Electromagnetic Energy: The energy of an electromagnetic field

22. Law of Conservation of Energy • The total energy of a particle is the sum of its kinetic and potential energies • Energy can neither be created nor destroyed

24. B: Elements and Atoms • Approximately 5000 years ago, philosophers wondered what would happen if they cut matter down into ever smaller bits • Like those Matryoshka dolls • What is the smallest point they could reach before whatever they were cutting was no longer recognizable as the starting material • The word “atom” comes from the Greek words “atomos” which means not divisible

25. Dalton and the Concept of the Atom • In 1807, John Dalton looked at many different compounds ands determined that they had regular patterns • Water had 8g of oxygen for every 1g of hydrogen • Hydrogen peroxide had 16g of oxygen for every 1g of hydrogen

26. Dalton’s Atomic Hypothesis • All atoms of a particular element are identical • Atoms of different elements have different masses • A compound is a specific combination of atoms of more than one element • In a chemical reaction, atoms are neither created nor destroyed; they exchange partners to produce new substances These tenets were first proposed 202 years ago and they are all true!

27. All matter is made up of various combinations of the simple forms of matter called the Chemical Elements. An element is a substance that consists of only one kind of atom.

28. The Nuclear Model of the Atom First proposed by Rutherford based upon his alpha particle experiment in 1911 Helped to explain his observation that 99% of alpha particles passed through gold foil without hitting anything

29. Atomic Number • The Atomic Number, Z, of an element is the number of protons in the nucleus. Hydrogen: Z=1, therefore it has _ protons Oxygen: Z=8, therefore it has _ protons Cesium: Z=55, therefore it has _ protons

30. Mass of an Atom • Using mass spectrometers (we’ll discuss later), we have determined the mass of individual atoms of most elements. • We can use the values to determine how many atoms are in a sample.

31. Isotopes • Mass spectrometers also allowed us to observe that every element had a couple of different masses in the sample. • This observation led to the discovery of chargeless particles in the nucleus called neutrons • Except for the lack of charge, neutrons and protons are nearly identical.

32. The sum of the number of protons and neutrons is the Mass Number, A, of the atom. • Example: Neon

33. Examples: Atomic and Mass Numbers • How many protons, neutrons and electrons are in a sample of Oxygen-18?

34. The Organization of the Elements • As of today, there are 117 known elements • Some are manmade, with Technetium created in 1937. • Some exist for a few microseconds.

35. The Periodic Table • In 1869, Dmitri Mendeleev discovered that the elements show PERIODIC trends in properties. • He organized the elements based upon these observations and today, we have the…

36. The Periodic Table

37. Metals, Nonmetals and Metalloids • Most elements are solid at room temperature and pressure • 11 are gases (N, O, Fl, Cl, H, Noble gases) • 2 are liquid (Br, Hg) • Metals: Conduct electricity, are malleable and ductile • Non-metals: Do not conduct electricity, are not malleable or ductile • Metalloids: Have some physical properties of metals, but behave chemically as a non-metal