The Subject of Chemistry Studies Matter, its structure and properties, and how it changes Define matter: Matter is anything that has mass and occupies space Mass vs. Weight Two properties of matter –Inertia is one –No two pieces of matter can occupy the same space at the same time

Classification of Matter Our starting point is a SUBSTANCE What is a Substance? Matter that has a uniform and unchanging composition Uniform = Homogeneous (same throughout) Unchanging =has a composition that is definite

Classification of Matter… Continued Said another way… has the same analytical results each time, that is, has the same composition each time Regardless of the sample site (where you sample the material) the proportions for the components is always the same

Classification of Matter… Continued Example- pure table salt is the chemical sodium chloride; no matter where you obtain a sample of it, the percentages for sodium and chlorine are the same- sodium = 40% and Chlorine 60%

Classification Scheme

Mixture = a physical blend of two or more substances in any proportion in which each substance retains its own individual properties or characteristics Important chemical consideration: mixtures can be separated by physical means, that is, does not require chemical reactions

Types of Mixtures Heterogeneous Mixture = a mixture that does not have a uniform composition and in which the individual substances remain distinct Homogeneous Mixture = a mixture that has a uniform composition throughout and always has a single phase, also known as a solution

Types of Substances Element = a substance that can not be broken down into simpler substances by chemical means Compound = a substance that can be broken down into simpler substances by chemical means and has different properties from the simpler substances

Another Viewpoint

This Scheme… Starts with, “Is it uniform throughout”? Or said another way, “Is it Homogeneous or Not Homogeneous? Not homogeneous is termed Heterogeneous and is defined as Not having the same composition throughout Such as Pepper and Salt added together There are pockets of both;

First Question………Continued As a result, you could get two different percentages of salt and pepper when analyzing different samples taken from the pile Furthermore, both the salt and pepper retain their characteristics such as color, and shape This is an example of one MIXTURE type called a Heterogeneous Mixture

Second Question… Can it be separated by physical means*? Takes advantage of the property of a mixture whereby it can be separated by such actions as: –Evaporation- Distillation –Filtration- Magnetism –Dissolving one component into a liquid that does not dissolve the other –Centrifugation * Also called mechanical means

Third Question… Simply takes advantage of the property of elements that they can not be decomposed (broken down) into any simpler substances

Properties of Matter Property = those characteristics that are responsible for a substance’s unique identity Types– physical and chemical Physical Property- is a characteristic that can be observed or measured without changing the sample’s composition Examples: ShapeColor Solubility Weight Boiling Point Physical State Density Freezing Point Odor

Density…a physical property Density is the amount of matter in a given space Remember that space is a synonym for volume Therefore density is the amount of matter per unit volume Said another way, it is the number of grams in 1 unit of volume (1mL or 1cm 3 )

Determining Density… Simply take the number of grams and divide that value by the volume in mL or cm 3 occupied Example, if the volume occupied by 15 grams is 6 mL then our density is 15 g ÷ 6 mL = 2.5 g/ mL Two kinds of data sources for density problems: direct (as above) or indirect

Indirect Sources for Volume Given the dimensions an regularly shaped object V = L x W x H (block) V = 4/3 π r 3 (sphere) V = 2 π r 2 (cylinder) Using the displacement of water by an irregular object: V = Final volume – Initial Volume

Importance of Density Density provides a way of comparing samples of different masses or volumes Because you are always setting the volume to one regardless of the starting mass or volume of the sample Density is the conversion factor between the mass of an object and its volume

For example, if mercury has a density of 13.6g/mLfthen we can say that 1 mL Hg = 13.6 g Hg (our conversion factor) Another example, the density of sulfuric acid is 1.84g/mL, we can write this as the conversion factor 1 mL H 2 SO 4 = 1.84 g H 2 SO 4 Let’s solve some density problems using PACKAGE REASONING

Package Reasoning… Given mass of a substance whose density is known, determine its volume Simply determine the number of gram packets that will fit into the given mass; this will give you the volume If you start with 15 grams and the density is 3g/cm 3, you can fit 5 packages giving you 5cm 3 for your answer– see below

Given the volume of a substance whose density is known, you can package the total volume into single units and then add the mass of each unit using the density Example, if you have 3 mL of a liquid whose density is 7 g/mL, the mass is? 7g 7g 7g = 7g x 3 = 21 g

Factor-Label Solutions… Key here is to use the given density as a conversion factor as already seen Example: What is the mass of 10 cm 3 of lead given its density of 11.4 g/cm 3 ? Solution: 10 cm3 Pb x 11.4 g Pb = 114 g Pb 1 cm3

Given 731 grams of tin whose density is 7.31 g/cm 3, how much space does it occupy in cubic centimeters? Solution 731 g Sn x 1 cm3 Sn = 100 cm g Sn

Last Resort…Formula D = M/V D is the density in g/cm 3 or g/mL M is the mass in grams V is the volume in cubic centimeters or milliliters You can rearrange the formula algebraically solving for M or V Requires only math skills; no chemistry understanding

Dr Rick’s Recommendation For understanding - it’s Package Reasoning For Ease of Calculation with little danger of setting it up incorrectly – it’s Factor- Label For the Utterly Confused it’s the Density Formula

States of Matter… Daily experience only three: Solids, Liquids and Gases The universe is mostly made up of the fourth which is Plasma which is defined as, “ a highly electrified collection of atomic nuclei and free electrons” Define a Solid, a Liquid and a Gas

Change of Phase… In order to change from one physical state to another there must be a change in the amount of energy in the system To go from a solid to a liquid you must add energy (heat), likewise, to go from a liquid to a gas also requires the addition of heat energy

Going in the opposite direction requires the removal of energy – that is, heat loss So what is energy? The ability to cause change The derived SI unit for energy changes is the joule (J) and is defined as the amount of energy exerted when a force of one newton is applied over a displacement of one meter.newton Makes perfect sense, does it not?

NOT ! Ok Let’s backtrack to an older unit of measuring thermal energy- the calorie- you know the stuff counted when dieting One calorie is the amount of heat energy needed to raise the temperature of one gram of water one Celsius degree. Makes more sense does it not- well the folks setup a conversion between joules and calories as follows-

1 calories = J, This is by definition so the number of sig figs is infinite for both values. How many joules are needed to raise the temperature of 1 gram of water from 14 o C to 15 o C? Answer… J How many joules are needed to raise the temperature of 10 grams of water one Celsius degree? Answer… J

Measuring Energy Changes Extrapolating, we come up with this relationship: Heat Transferred = mass in grams x change in temperature x specific heat Specific Heat = the amount of thermal energy required to raise 1 gram of a substance 1 Celsius degree; for water it is J/g·C o

The Equation… q = m x ΔT x C P q is the Heat Gained or Heat Lost m is the mass in grams ΔT is the change in temperature in o C C P is the Specific Heat of the substance

Chemical Property- Those characteristic of a substance when it is involved in a chemical change Or: those characteristics that describe whether or not a substance can be changed into a different substance or can be broken down into simple substances by a chemical change

Chemical change ? The ability to combine with or change into one or more other substances The process is called a chemical reaction Verbs that indicate chemical change –Reacts with –Forms a new chemical –Oxidizes

Examples of chemical properties Acids neutralize bases forming water and a salt Oxygen reacts slowly with iron Silver nitrate when added to sodium chloride produces a white precipitate called silver chloride