Chapter 15-1 Categories & Composition of Matter PDF

Chapter 15 – 1 Categories & Composition of Matter Substances: Cannot be broken down into simpler components and still maintain properties of the original substance. TWO CATEGORIES OF SUBSTANCES:  Elements  Compounds Elements: Pure substances in which all the atoms are alike....

Chapter 15 – 1 Categories & Composition of Matter Substances: Cannot be broken down into simpler components and still maintain properties of the original substance. TWO CATEGORIES OF SUBSTANCES:  Elements  Compounds Elements: Pure substances in which all the atoms are alike. Elements cannot be separated into other substances.  ELEMENTS – are all listed on the Periodic table If a substance is not on the periodic table – it is not an element. Some pure substances have common names like diamonds. Click on the diamond.  Periodic Table of Elements There are 115 known elements. 90 of these elements are found in nature on earth. 28 others have been made in laboratories Compound:  A substance in which atoms of two or more elements are combined in fixed proportions.  The proportions of the elements in a particular compound are always the same.  The chemical formula shows the elements in a compound and the proportion of atoms of each element. Water = H2O (2 atoms of hydrogen combine with one atom of oxygen) Table sugar = C12H22O11 PROPERTIES OF COMPOUNDS & MIXTURES COMPOUNDS: When elements combine chemically, the compound formed is a totally new substance. The physical (and chemical) properties of a compound are completely different from the properties of the elements that make up the compound. MIXTURES: The substances in a mixture are physically combined. Each substance remains distinct & keeps its own properties. The properties of the mixture will be a blending of the properties of the components that make up the mixture. Compounds: Substances are chemically combined to form new pure substances with new properties. (The chemical formula of the compound tells what elements are present & their proportions) Copper sulfate (CuSO4) is a crystalline compound made from the elements copper (metal), yellow sulfur powder and oxygen gas, which are all totally different from the blue copper sulfate crystals formed when atoms of the elements bond chemically. sulfur copper sulfate  The properties of a compound are completely different from the properties of the elements that make the compound. (White salt crystals are made from yellow-green, toxic Chlorine gas and Silver-colored, highly reactive Sodium metal.) Salt = NaCl  Riddle ?!?!? Two liquids contain only hydrogen and oxygen, and both liquids are transparent and colorless. How can the two liquids have different identities? They have different combinations of atoms. One liquid is water = H2O The other is hydrogen peroxide = H2O2  A mixtureMixture is made up of two or more substances mixed in any proportion.  The substances in a mixture are not chemically combined and can be easily separated by physical means.  For example, salt can be separated from salty water by boiling the water off.. Mixtures: Substances are blended physically. In iced tea, you can taste each component of the tea separately as each keeps its own properties. You can taste tea, sugar, lemon, mint all at the same time. You can also mix them in any proportion. CATEGORIES OF MIXTURES 1. Heterogeneous mixtures 2. Homogeneous mixtures 3. Colloids Heterogeneous Mixtures A mixture in which the different materiasl can be easily distinguished. Most common type of mixture. Homogeneous Mixtures Two or more substances blended evenly throughout. - can be solids, liquids, or gasses Examples: Alloys, Soft drinks, Air SOLUTION:  A homogeneous mixture of particles that are so small that they can’t be seen with a microscope. (The particles are atoms or molecules.)  Solutions remain uniformly mixed and the particles will not settle or separate out. How concrete is made: click on the picture of a piece of concrete:  SOLUTIONS Note that solutions can be: Liquids in liquids: alcohol in water Solids in liquids: salt in water Gases in liquids: soda Gases in gases: air Solids in solids: alloys (brass, bronze) Alloys are not transparent like solutions, but are evenly mixed throughout and are made of individual atoms. This is why they are categorized as solutions. (They are made by melting the solids, mixing, then cooling the mixture) ALLOY: A mixture of a metal with other elements to form a solid solution. Bronze 88% copper, 12% tin Stainless steel Iron, Carbon, Chromium (and other metals) Pewter Tin, Copper, Antimony Bismuth, lead Brass 67% copper, 33% zinc Suspension A heterogeneous mixture containing a liquid in which visible particles settle. For example: Italian Salad Dressing. You will see some seasonings and other particles floating around. They don't dissolve. Instead, each of these particles is suspended in the oil and vinegar but still visible. The particles that are more dense than the vinegar & oil will settle to the bottom of the bottle. Muddy Pond Water is a suspension. (The mud will settle to the bottom.)  COLLOIDS  A type of mixture in which the particles do not settle.  Usually opaque.  Particles in a colloid are large enough to scatter light, this is called the Tyndall effect. Colloids cont..  A colloidal system is not a true solution but it is not a suspension either because it does not settle out like a suspension will over time.  The particles are larger than those of a solution but smaller than a suspension.  They range in size from 1 nm to 1 μm. CLICK HERE FOR MORE EXAMPLES OF COLLOIDS Colloids