Chapters 1 and 3 Chemistry: The Study Of Matter Part 2

Physical and Chemical Changes Include all phase changes, dissolving, and changes in size or shape Includes rusting, tarnishing, burning, reactions with acids, etc. Physical Changes:Chemical Changes: No new materials formAlways form new materials (Composition is unchanged)(New composition!)

Conservation of Mass always equals In any chemical change, it has been shown that the total mass of the substances BEFORE the reaction always equals the total mass of the substances AFTER the reaction! Mass is never created, nor is it destroyed! This is called “The Law of Conservation of Mass”

Chemical Reactions Always Produce Chemical Changes Signs of a chemical reaction (chemical change) Each of these is a sign that new substances with new properties have been formed! 2. Production of heat and/or light energy 3. Formation of a precipitate (new solid product) 4. Production of a new gas (or a new odor) 1. Color change (new color - not a mixture!)

Color change - a new color!

Production of Heat and/or light

Precipitation: Two soluble substances combine to form an insoluble substance!

Production of New Gases

Physical Properties Physical properties can be observed without changing the material being studied. Crystal structure M.P. = °C ( °F)] Therefore, solid at room temperature! B.P. = 2162 °C (3924 °F) Good electrical conductor Metallic luster Color = “silver” Density = g/cm 3 Taste - none Odor - none Insoluble in water silver

Extensive properties depend on the amount of substance. Ex: mass depends upon the amount of substance, and is an extensive property. There are two types of physical properties… Extensive and Intensive Properties Length and volume are also extensive properties.

Intensive properties are independent of the amount of substance present. Density is an example of an intensive property of matter. The density of a substance is the same, no matter how much substance is present. Other intensive properties include color, melting point, and boiling point, among others.

Using an Intensive Property – Panning for Gold Because gold is so dense (19 g/cm 3 ), it can be separated from sand by swirling in water. The sand washes over the edge, while the more dense gold remains in the pan.

DuPont uses the same technique to separate the more dense titanium dioxide from ordinary sand at the Trail Ridge site here in Starke! Their “pans” are long spirals. The water and sand swirl down, with the more dense titanium dioxide staying near the center. Slots at the center capture the titanium dioxide, while the less dense sand swirls to the outside, and eventually, to the bottom, and back to the soil.

Chemical Properties - how (or if) a substance reacts, and what new substances form. Examples: Reactions with other substances: (air, water, acids, etc) (The Statue of Liberty is actually made of copper!) Silver metal tarnishes (forms silver sulfide) in air Flammability: Chemical Properties

More Examples: Many metals and marble (stone statues and headstones) all react with the acid in acid rain… Chemical Properties

Elements “Elements” are given that name because they are “elementary” – the simplest form of matter. Because they are elementary, they cannot be broken down by chemical changes or reactions! There are only about known elements, yet all the different kinds of matter in the universe are made from these “building blocks”. (Like the millions of words in English are formed by just the 26 letters of the alphabet). Elements are classified as “metals”, “nonmetals”, and “metalloids”.

The Elements The elements are arranged in the Periodic Table by their properties! Elements with similar properties are found in vertical columns.

Compounds “Compounds” are chemical combinations of elements. always Any particular compound will always have the same elements, in the exact same ratio! NEW DIFFERENT Compounds have NEW properties, that are DIFFERENT from the elements that make them up! Because they are chemical combinations of elements, compounds can only be broken down by chemical changes!

The Law of Definite Proportions Since any compound always has the same elements in the same ratio… …the percentage of each element in that compound is constant! Example: in grams of sugar there are 8.44g of carbon, while grams of sugar contain 0.633g of carbon. 8.44g C x 100 = 42.2%C 20.00g 0.633g C x 100 = 42.2%C 1.500g

Is a Substance An Element or Compound? Elements CANNOT be broken down by ordinary chemical reactions! Heating or electricity CANNOT change an element! Compounds WILL BREAK DOWN with either heat or electricity, (or both). E + heat -> E E + elect -> E C + heat -> A + B C + elect -> A + B Substances can be either elements or compounds: How can we test a substance to tell?

Mixtures Mixtures can be heterogeneous or homogeneous. In either case, the mixture is only a physical combination of materials. This means each component (part) of a mixture keeps its own properties! Separating the components of a mixture involves their physical properties only! Separation techniques include: Filtration, crystallization, chromatography and distillation, among others.

Separating Mixtures Filtration: one component will dissolve, the other(s) will not. Crystallization: one component will form crystals, the other(s) will not. Chromatography: each component is attracted to the liquid phase differently than the others. Distillation: each component has a different boiling point.

Mixtures vs. Compounds Mixtures are PHYSICAL combinations of substances. Compounds are CHEMICAL combinations of substances Mixtures have properties that are combinations of their components Compounds have new and different properties from their components Mixtures are easily separated by physical changes Compounds can only be separated by chemical changes! A mixture can have many ratios of components A compound has only ONE ratio of components

Chemical Language 2 Fe + 3 S  Fe 2 S 3 A Chemical Equation Element symbols Compound Formula reactantsproducts Note that element symbols ALWAYS start with a UPPER CASE LETTER. If a second letter is in the symbol, it is lower case!

The Diatomic Elements There are seven elements that, when not in compounds, are ALWAYS found as “diatomic elements”! They are: Hydrogen (H 2 ) Oxygen (O 2 ) Nitrogen (N 2 ) Fluorine (F 2 ) Chlorine (Cl 2 ) Bromine (Br 2 ) Iodine (I 2 ) A memory tip: “HON, the halogens”! Example: H 2 + Cl 2  2 HCl