Chapter 1
Chemistry is the Study of Matter. Chemistry is concerned with the properties of chemicals and with the changes that chemicals can undergo.
Any substance that has a definite composition – it is always made of the same “stuff”, no matter what state it is in or where you find it. Some occur naturally, like water, oxygen, and carbon dioxide. Some are manufactured like polyethylene, acetone, acetaldehyde, and sodium hydroxide. Some, like aluminum and copper, are taken from natural elements.
Anything that changes chemicals. A natural part of life. Chemical reactions are necessary for: ◦ Things to grow ◦ Things to decay ◦ Food to cook ◦ Engines to run ◦ Food to digest
The way that particles are arranged determines the properties of the matter Most of the matter that we will talk about is in three states: Solids, liquids, and gases
Fixed shape Fixed volume Rigid in structure Slight vibrations Strong attraction between particles
Fixed volume Variable shape Particles slip past one another Takes the shape of its container Particles are held together loosely
Variable shape Variable volume Particles move independently of one another Fills any container it occupies Particles are far apart and are not attracted to each other
The identity of the substance does not change Change of state can occur – particles speed up or slow down, arrangement of particles changes Melting, freezing, crushing, dissolving, tearing, chopping, etc.
Identities of substances change and new substances form. Reactants – substances used in a reaction Products – substances formed in a reaction Burning, rusting, precipitate formation (solid substance forms, may be a cloudy liquid), evolution of gas (indicated by bubbles or odor), color change, etc.
Endothermic – This change in matter requires or uses heat. ◦ Melting, boiling ◦ Energy is absorbed ◦ Temperature of substance increases Exothermic – This reaction releases heat. ◦ Freezing, condensation ◦ Energy is released ◦ Temperature of substance decreases
The Law of Conservation of Matter states that Matter cannot be created or destroyed. When a change occurs, whether Physical or Chemical, matter is not created or destroyed!
What is a chemical? Which state of matter has a fixed shape and volume? Which state of matter has a fixed volume but takes the shape of its container (variable)? What type of change does not change the identity of the matter? What term is used to identify the substances you begin with in a chemical reaction?
List four changes that indicate a chemical change might have occurred. List four changes that indicate that a physical change might have occurred. What is the Law of Conservation of Matter? What does endothermic mean?
Anything that has mass and volume. Volume – the space that an object occupies Mass – the quantity of matter contained in the object Weight – is NOT Mass – they are related, but weight is dependent on gravity. Therefore, weight is dependent on location, mass is not. We will use Mass in Chemistry!
Matter is made of atoms An atom is the smallest unit of an element that maintains the properties of that element
Quantity (symbol)Unit (abbreviation) Length (l) Mass (m) Time (t) Amount of a substance (n) Electric Current (I) Temperature Meter (m) Kilogram (kg) Second (s) Mole (mol) Ampere (A) Kelvin (K)
Since 1 gram = 1000 milligrams We can write it as a conversion: 1 gram OR 1000mg 1000 mg 1 gram
Page 14, # 1 - 3
Can be determined without changing the nature of the substance Color, state, texture, temperature, melting point, boiling point, density What are the physical properties of ◦ Your desk ◦ Sugar ◦ A sheet of notebook paper
Identified by trying to cause a chemical change Reactivity with oxygen, reactivity with acid, flammability
Mass divided by Volume Is not dependent on the size of the sample Relationship is linear: The slope of a line represents the density of a substance when the volume is plotted on the x-axis and the mass is plotted on the y-axis. Can be used to identify a substance Chart on p. 17 gives densities of substances
A piece of tin has a mass of g and a volume of 2.26 ml. What is the density of tin? A man has a 50 ml bottle completely filled with 163 g of slimy green liquid. What is the density of the liquid? A piece of metal has a density of 11.3 g/ml and a volume of 6.7 ml. What is the mass of the piece of metal?
Pure Substances ◦ Has characteristic properties that can be used to identify it (physical and chemical properties) ◦ Elements – contain only one kind of atom Can be single atoms or molecules (two or more atoms of the same kind) ◦ Compounds – contain more than one kind of atom Represented by formulas Molecules consisting of two or more atoms combined in definite ratios
Mixtures – A sample of matter that contains two or more pure substances ◦ Most foods and air are mixtures. Sugar and salt are not, water is not ◦ Can vary in composition and properties ◦ Homogeneous Mixtures Pure substances are distributed evenly throughout the mixture (gasoline, air, syrup, tea) ◦ Heterogeneous Mixtures Substances are not evenly distributed (orange juice, chocolate chip cookie, salad)
Quantitative measurements involve numbers (quantities). Qualitative measurements involve observations (color, shape, texture)
An Atom is the smallest unit of an element that maintains the properties of that element An Element is a substance that cannot be separated or broken down into anything simpler A Molecule is the smallest unit of a substance that keeps all of the properties of that substance (can be made of more than one atom)
Compound – ◦ Chemically joined ◦ Properties different than that of components ◦ Definite ratio of components Mixture – ◦ Physically mixed together, not chemically joined ◦ Properties of components are maintained ◦ Varying ratio of components
Pure substances Matter Mixtures Compounds Elements Heterogeneous Homogeneous
Separated by physical properties Filtration, sorting, distillation, evaporation, using magnetic properties How would you separate the following mixture? Iron filings, sand, water, salt, and pepper