Properties of Matter Chapter 2

Pure Substance – matter that has exactly the same composition; sometimes called simply a substance Substances can be classified into two categories – elements and compounds. Element - a substance that cannot be broken down into simpler substances. An element has a fixed composition because it contains only one type of atom. Atom - the smallest particle of an element

1. The first letter is always capitalized. Symbols for elements - to make it easier to write chemical equations, elements are represented by 1 to 3 letters. An element’s symbol does not necessarily start with the same letter as the element itself. 1. The first letter is always capitalized. 2. If there is a second or third letter, the letter is not capitalized. Element name Element symbol Hydrogen H Helium He Mercury Hg Tin Sn Gold Au Ununbium Uub

always contains two or more elements joined in a fixed proportion Compounds – a substance that is made from two or more simpler substances and can be broken down into those simpler substance. The substances that are joined in a compound are bonded chemically. The properties of compounds differ from those of the substances from which it is made. always contains two or more elements joined in a fixed proportion At room temperature, hydrogen (H) and oxygen (O) are gases. But when chemically combined to form H2O (water), they become a liquid at room temperature. Sodium is about as hard as cold butter and can be cut with a sharp knife. Sodium melts at about 98˚C. At room temperature, chlorine (Cl) is a yellowish gas that if inhaled, can kill you. But when chemically combined to form NaCl (sodium chloride), it is everyday table salt that you eat. Pound Cake Recipie vs. Salsa

804 feet long, Filled with Hydrogen. Hindenburg LZ129 German airship built 1930s. largest airships & largest flying vehicles, considerably faster than ocean liner, more comfortable, longer-ranged than the airplane, 804 feet long, Filled with Hydrogen. catastrophic crash 6 May 1937 in Lakehurst, NJ. Static Electricity - Skin Flammability – Tension wire snapped & ruptured H+ cells ??? 35 of 97 died (1 ground crew) http://www.indyarocks.com/videos/Hindenburg-disaster-footage-535035 http://www.britannica.com/EBchecked/media/127569/The-Hindenburg-airship-caught-fire-at-Lakehurst-NJ-May-6

mixtures – substances consisting of two or more substances that have been combined without chemical bonding taking place The properties of a mixture can vary because the composition of a mixture is not fixed. Mixtures can be classified by how well the parts of the mixture are distributed throughout the mixture.

The two basic types of mixtures are heterogeneous and homogeneous. heterogeneous mixture – mixture in which the parts of the mixture are noticeably different from one another homogeneous mixture – the substances are so evenly distributed that it is difficult to distinguish one substance from another. Based on the size of its LARGEST particles, a mixture can be classified as a solution, suspension, or colloid.

solution – when substances dissolve and form a homogeneous mixture suspension – a heterogeneous mixture that separates into layers over time (i.e. – medicines – “shake well before using”) colloid – contains some particles that are intermediate in size between the small particles in solution and larger particles in a suspension.

Solution Suspension Colloid homogenous heterogeneous will not separate into layers separates into layers particles can NOT be trapped by a filter particles CAN be trapped by a filter does NOT scatter light scatters light

Physical Properties any characteristic of a material that can be observed or measured without changing the composition of the substances in the material. viscosity – the tendency of a liquid to keep from flowing, its resistance to flowing The greater the viscosity, the slower the liquid moves. The viscosity of a liquid usually decreases when it is heated.

conductivity – a material’s ability to allow heat to flow Materials that have a high conductivity, such as metals, are called conductors. If a material is a good conductor of heat, it is usually also a good conductor of electricity. Materials that have a low conductivity, such as wood, are called insulators. If a material is a good insulator of heat, it us usually also a bad conductor of electricity.

brittle – easily broken when hit; glass is a brittle object malleability – the ability of a solid to be hammered without shattering (piece of pure gold the size of a matchbook can be pounded flat until it is large enough to cover a regulation-size tennis court.) brittle – easily broken when hit; glass is a brittle object hardness – how hard a material is; a diamond is the hardest known material with a rating of 10 and it is made of the element carbon http://www.goldkit.com/Five_Gold_Myths.asp http://blainewhipple.com/wp-content/uploads/2010/06/statue_of_liberty_04.jpg http://eclectorium.files.wordpress.com/2011/01/sundae_332w1.jpg

Melting point – the temperature. at which a substance changes Melting point – the temperature at which a substance changes from solid to liquid; for water this change normally occurs at 0° C. Freezing Point - ? Boiling point – the temperature at which a substance boils; for water this change normally occurs at 100 ° C. When substances such as salt are dissolved in water, the boiling temperature is raised ↑

When a material melts or changes into a gas at its boiling point, it is undergoing a phase change. This is a physical change NOT a chemical change.

Substance Melting Point Boiling Point Hydrogen - 259.3 ° C - 252.9 ° C Nitrogen - 210.0 ° C - 195.8 ° C Ammonia - 77.7 ° C - 33.3 ° C Water 0° C 100 ° C Table Salt 800.7 ° C 1465 ° C Gold 1064.2 ° C 2856 ° C

Physical properties are used to identify a material, to choose a material for a specific purpose, or to separate the substances in a mixture . Using properties to identify materials. The steps use to identify a material are similar to the steps used to test for purity. Step 1. decide what properties to test Step 2. do tests on a sample of the unknown Step 3. compare the results with the data reported for known materials

Using Properties to Separate Mixtures filtration – process that separates materials based on the size of their particles distillation – a process that separates the substances in a solution based on their boiling points

Recognizing Physical Change physical change – change that occurs when some of the properties of a material change, but the substances in the material remain the same Some physical changes can be reversed. Examples: braiding and unbraiding your hair; knotting and unknotting a rope Some physical changes cannot be reversed Examples: putting back together an apple that has been cut in half, putting hair back after cutting it

Chemical Properties Chemical properties include those that cannot be observed without changing the composition or make-up of the material. A strong example of a chemical property is the ability of something to burn. chemical property – any ability to produce a change in the composition or make up of matter

flammability – a matter’s ability to burn in the presence of oxygen; flammability – a matter’s ability to burn in the presence of oxygen; no oxygen = no burning reactivity – property that describes how readily a substance combines chemically with other substances A material may be selected for its use based on whether it has a high or low reactivity to some particular substances.

Chemical Changes chemical change – change that occurs when a substance reacts and forms one or more new substances. Three common types of evidence for a chemical change are a change in color, the production of gas, and the formation of a precipitate. Changes in color can occur immediately or over a period of time. Sometimes, the longer the chemical change has to react, the more color change occurs.

A common example of a production of gas is mixing Alka Seltzer into water or mixing baking soda and vinegar. The bad smell that is produced when food rots or milk turn sour are examples of a chemical change and a production of gas.

precipitate – any solid that forms and separates form a liquid mixture A common example of a precipitate being formed is when acid is added to milk. This is how cottage cheese is made.

Which one is it? When matter undergoes a chemical change, the composition of the matter changes. When matter undergoes a physical change, the composition of the matter remains the same.