Chapter Two: What are the properties of elements?

1. Chapter Two: What are the properties of elements?

2. Science question of the day… • Why does cutting onions make you cry?

3. Answer!!! • When you cut into an onion, a powerful acid sprays up into the air. If your eyes are in the way of the spray (which is likely if you are cutting onions), the acid, while not damaging to your skin, will cause your eyes to sting. Immediately, your lacrimal glands or tear glands, go into overdrive. Your eyes start to tear, and tears continue in excess until they’ve successfully gotten rid of the irritation. Cool, huh?

4. Physical Properties of Matter • Although everything is made of matter, they all have different properties. • Remember our metals vs. non-metals experiment? • Some properties we can test are physical properties – properties that can be observed or measured without changing the object, or any of the materials it’s made of.

5. Physical Properties • Some physical properties can change like mass and size depending on how much of the object you have. • Some physical properties never change like color, smell, magnetism, and melting and boiling points. • Take these items for example. What are the physical properties you notice that are alike and different?

6. Physical Properties • Texture is how the surface of the object feels. • Malleability is the ability of a substance to be bent or hammered into sheets without breaking. • Ductility is the ability of the substance to be made into thin threads without breaking. • Mass and Volume can be measured. We will learn how to do this later. This is not necessarily the weight! • Density is the amount of mass that fits in a given volume. • Buoyancy is the ability to float in a liquid or rise in a gas.

7. Time for a little practice… • Read “Physical Properties of Matter” and answer questions 1-4 for homework. Number 5 is bonus. This is due tomorrow!

8. Science question of the day… • Contrary to popular adult belief, kids do not make your hair turn gray, but what does?

9. Answer!!! • It’s hard to imagine that those lovely locks of blond or brunette hair on your head may someday change color so dramatically. But your hair doesn’t turn white from a lifetime of watching really scary horror movies. Instead, it’s actually revealing its natural beauty. Hair loses much of its color because it’s losing its melanin or carotene, which are your body’s natural coloring substances (also known as pigments). As you grow older, the pigment production in hair follicles slows down and may eventually stop, cutting off your hair’s supply of coloring and making it appear gray or white. But your entire head of hair won’t turn gray overnight; after all, this is a process that takes about 10-20 years.

10. Physical Changes • Sometimes substances physical properties might change, but this does not make it a different substance. • Some physical changes are irreversible like cracking an egg or breaking glass. • Is this a physical change?

11. Physical Changes • Inset Video Here

12. Time for a little practice… • Read “Physical Changes of Matter” and answer questions 1-4 for homework due tomorrow!

13. Science question of the day… • Why is our galaxy called the “Milky Way?”

14. Answer!!! • The Milky Way Galaxy is named for its milky appearance. There’s a Greek poem that describes the galaxy as “that shining wheel, men call it Milk.” To the Greeks, the galaxy was called “Galaxiaskuklos,” or “Milky Band.” To the Romans, it was “Via Lactea,” or “Road of Milk.” The Greek word for milk is “gala,” and the word galaxy is derived from it. Human cultures have different names for the Milky Way, like “Celestial River” or “Celestial Road or Path.” It’s not really milk u up there though. It is mostly noble gasses that have accumulated together and reflect back light!

15. Physical Characteristics • Last chapter we talked about physical characteristics and using them to classify elements into their families. • Much like physical characteristics, we can also classify elements by their chemical characteristics. • Which chemical characteristic did we test last week? • I’ll give you a hint. It’s in your stomach, and it can also be used to make lemonade. Gross…

16. Physical and Chemical Characteristics and Changes • These different characteristics tell us what kind of reactions substances will have when energy is added or taken away. • Here is my example… • We know that water will boil when we add the right amount of heat. This is called the boiling point, and it is a physical characteristic of water. • This is a physical change in the substance.

17. Chemical Reactions and Changes • There are several physical changes that substances can go through. Let’s talk about this egg for example. What kinds of changes could it go through? • Which of these changes, if any, are irreversible? • How else could we change this egg?

18. What do I need for a chemical change to occur? • Most chemical changes either require energy or release energy. • When the egg cooked, it required energy in order to transform. • When we burn a candle, it releases two kinds of energy. What two kinds of energy are being released from my candle?

19. Chemical Properties: Changes • Just like physical changes, substances can undergo chemical changes as well. • You know you have a chemical change when new substances are formed. • This happens when the atoms are rearranged. The same atoms are there, they are just put together differently. • Take the egg for example. When we cooked it, what observations can you make about this cooked egg?

20. Chemical Reactions • When we have a chemical change (like cooking the egg to form a new substance) we create a chemical reaction. • The heat caused the chemicals in the egg to react and become a solid. • Does this type of reaction require energy or release energy? • It is called an endothermic reaction. It absorbs energy from its surroundings.

21. Chemical Reactions • We have another chemical reaction with my burning candle. • The wick lights and burns the wax, and part of the wax becomes a gas. • Does this type of reaction require energy or release energy? • It is releasing energy! The wax requires energy to melt and become a gas (physical change), but the wick is creating energy to burn the wax • A reaction that creates energy is called exothermic. • Can you think of any other words that use the prefix ‘exo’?

22. How do I know it’s a chemical change and not a physical change? Physical Chemical • Observable and Measurable • Buoyancy -Mass • Malleability -Volume • Texture -Density • Shape -Melting Point • Ductility -Boiling Point • color • New substance formed (not a change of state!) • Release or absorption of energy • Color change • Light or heat given off • Bubbles

23. Physical vs. Chemical Changes

24. Next week… • Next week you and a partner will determine what physical and chemical changes can occur! You will be given a bag of several items and you will experiment to determine how you can change them. • You will then create a Prezi to share with the class to show your chemical and physical changes. • Think about some ingredients and substances at home this weekend that could be used to create physical and chemical changes.

25. Time for a little practice… • Read “Physical Changes vs. Chemical Changes” and answer questions 1-4. Number 5 is bonus!

26. Science question of the day… • Why is there no gravity in space?

27. Answer!!! • Oh, but there is gravity in space! Astronauts only FEEL like there is no gravity because they are continuously falling as if there weren’t. You see, if there were no gravity in space, the astronauts in their space ships would fly off into space and not be able to come back!

28. Imagine you have a piece of string with a ball on the end. In this example, YOU are the EARTH, the STRING is GRAVITY, and the BALL is a SPACE SHIP. Now start swinging the ball around in a circle. You see that the ball is pulling on you as you are pulling on the ball. If you were to cut the string (that is, if there were no gravity), then the ball would fly off into space.

29. The difficult thing to realize is this: if you are constantly pulling on the string — which you are as you swing it around — why doesn’t the ball come to you as it swings? It is because the ball is already in motion around you. This is like the space ship; it is in motion around the earth, and is continuously “falling” towards the earth as the earth’s gravity pulls on it.

30. Characteristics of Chemical Change • Whether or not a substance can go through a chemical change is dependent on its chemical properties. • The ability to burn is called combustibility. • Wood, coal, candles, paper, etc. all have this chemical property, and therefore can go through chemical changes by being set on fire!

31. Characteristics of Chemical Change • Another chemical property of elements is reactivity. • Reactivity is how volatile an element is with other elements. • For example, the first column of the periodic table contains highly reactive elements. They are looking to pick fights with other elements and create explosions!

32. Characteristics of Chemical Change • Another chemical property is stability. • Stability is used to describe elements that do not react easily with other substances. • The noble gases in the far column of the periodic table are examples of stable elements. • Stable elements very rarely go through chemical changes.

33. What are chemical reactions? • There are four types of chemical reactions that occur to create a chemical change: combustion, decomposition, double replacement, and oxidation.

34. Chemical Reactions: Combustion • A combustion reaction is an exothermic reaction in which a substance combines with oxygen. • It produces heat and light, like when a log is lit by a match. • The heat ignites the oxygen and other elements in the wood which then burns and creates a new substance: ashes.

35. Chemical Reaction: Decomposition • A decomposition reaction is when a substance is broken down into simpler substances. • We see this when old trees rot in the woods. They break down into the simpler elements they are made of. • Another example if when an electric current is passed through water. The electricity (energy) breaks the water down into hydrogen and oxygen. • Don’t try that at home!

36. Chemical Reactions: Double Replacement • A double replacement reaction happens when ionic compounds exchange ions with each other. • This happens when two ionic compounds combine to form one substance like sodium and hydrogen chloride. • They combine and form sodium chloride. • Without this kind of reaction we wouldn’t have water! Hydrogen and hydroxide ions combine to form molecules in H2O!

37. Chemical Reactions: Oxidation • An oxidation reaction occurs when a substance loses electrons . • This can happen in several ways, but we see this most commonly when metals react with hydrogen and oxygen in air and water. • This is what produces rust on nails and the green tarnish on copper.

38. Time for a little practice… • Read “Chemical Changes and Chemical Properties” and answer questions 1-4. Number 5 is not bonus because we will be doing this in class.

39. Time for an Experiment… • You will be analyzing substances to determine how they can go through physical and/or chemical changes. • Each group will be given a bag of items and substances. Experiment with them and hypothesize what will happen when they are combined or changed by each other. • You will have two days to complete your experiment.

40. Science question of the day • How do glow sticks glow?

41. Answer!!!

42. Mixtures • We have learned that pure substances are made of the exact same element. No matter how you look at it, it will always be the exact same makeup. • But, in Chemistry, we can combine elements to make compounds. They are no longer pure substances. • Compounds are formed through chemical changes, but even more common in nature are mixtures.

43. Mixtures • Mixtures are combinations of two or more pure substances that are not chemically combined with one another. • They do not have to be in the same proportions. • No matter how well they are blended together, their molecules remain unchanged. They do not combine! • Some mixtures are easy to identify because you can see their individual substances. • Think about the trail mix…

44. Solutions • Solutions are a bit different from mixtures. • In a mixture, the components can be added in different sizes and proportions. • In solutions, the components are mixed in equal proportions. • For example, if I took my trail mix and added the same number and weight of raisins, nuts, and M&Ms it would be a solution instead of a mixture.

45. Solutions • Solutions can be made from solids, liquids, or gasses. However, the most common solutions are solids that are dissolved in liquids. • Look at my Stevia. It is a solid. • Look at my water. It is a liquid. • The water is dissolving my sugar as I pour it in. This is called my solvent. You “solve”nt for the solution! • The sugar that is dissolved is called my solute.

46. Mixtures and Solutions

47. Time for a little practice… • Read “ Mixtures and Solutions” and answer questions 1-4. Number 5 is a bonus question.

48. Science question of the day… • Why do fireflies light up?

49. Answer!!!

50. Separating Mixtures • Since substances do not go through chemical changes, they can be separated quite easily. • They can be separated because of their physical properties. To illustrate how mixtures can be separated using physical properties we will do a little experimentation!