Laws and theories Law – a generalization that describes the behavior of nature. i.e. Newton’s Laws of Motion Law of Definite Proportions Law of Definite Proportions Theory – an explanation of observations i.e. Darwin’s Theory of Evolution Dalton’s Atomic Theory Dalton’s Atomic Theory

Classes of matter Matter Pure substancemixture elementhomogeneouscompoundheterogeneous

Solutions Solutions are homogeneous mixtures. A solute (the dissolved substance) is put in a solvent (the dissolving substance). The solvent is the substance there is more of.

Examples elements compounds homo mix hetero mix Carbon waterairconcrete Carbon waterairconcrete Iron carbon dioxidesalt watermilk Iron carbon dioxidesalt watermilk Gold table salt (NaCl)white goldwood Gold table salt (NaCl)white goldwood Mercury aspirinbrasssand Mercury aspirinbrasssand

General classes of elements Metals – have luster (shine) Metals – have luster (shine) are malleable (not brittle) are ductile (can be drawn into wires) conduct heat and electricity Nonmetals- poor conductors of heat and electricity Nonmetals- poor conductors of heat and electricitybrittle Metalloids- have characteristics of metals and nonmetals Metalloids- have characteristics of metals and nonmetals

Brown, LeMay, Burstein “Chemistry: The Central Science

Chemical symbols First letter is always capitalized. First letter is always capitalized. Second letter, if there is one, is never capitalized. Second letter, if there is one, is never capitalized. Co and CO are very different! Co and CO are very different! Some elements use the Latin name Some elements use the Latin name 2O means 2 oxygen atoms O 2 means two oxygen atoms are chemically bonded together.

Law of Definite Composition- Every compound has a definite composition by weight. - the % weight of each element in a compound is always the same.

Physical properties Can be determined without changing the identity of the material Can be determined without changing the identity of the material Freezing point Freezing point Boiling point Boiling point Color Color Odor Odor Hardness Hardness Density Density Solubility Solubility

Extensive Properties Extensive Properties Depend on how much (the extent) matter there is Depend on how much (the extent) matter there is i.e. length, mass, volume i.e. length, mass, volume Intensive Properties Intensive Properties Do NOT depend on how much matter there is Do NOT depend on how much matter there is i.e. temperature, density (m/V) i.e. temperature, density (m/V)

Steel Adding the following elements (besides carbon) to iron produces steel with these resulting properties. Adding the following elements (besides carbon) to iron produces steel with these resulting properties. Cr - adds corrosion resistance Cr - adds corrosion resistance Si - improves machinability and weldability Si - improves machinability and weldability V - adds strength V - adds strength Mo - adds strength Mo - adds strength Ni - changes the microstructure, can improve toughness Ni - changes the microstructure, can improve toughness Nb - improves creep resistance with proper heat treatment Nb - improves creep resistance with proper heat treatment Al - removes oxygen to improve strength Al - removes oxygen to improve strength B - helps to prevent cracking B - helps to prevent cracking N - can improve strength by forming nitrides N - can improve strength by forming nitrides

Properties change at nanoscale Types of properties Types of properties Optical (e.g. color, transparency) Optical (e.g. color, transparency) Electrical (e.g. conductivity) Electrical (e.g. conductivity) Physical (e.g. hardness, melting point, diffusion rate) Physical (e.g. hardness, melting point, diffusion rate) Chemical (e.g. reactivity, reaction rates) Chemical (e.g. reactivity, reaction rates) Properties are usually measured by looking at large (~10 23 ) aggregations of atoms or molecules Properties are usually measured by looking at large (~10 23 ) aggregations of atoms or molecules

Chemical Properties Describe the behavior of a material in reactions that change its identity Describe the behavior of a material in reactions that change its identity Combustibility Combustibility Reactivity with other substances Reactivity with other substances

Which chemical and physical properties should a roofer consider when selecting material for a metal roof?

Physical Changes - are those in which the identifying properties of a substance are unchanged - Ex. : change of phase breaking, cutting breaking, cutting dissolving dissolving

Chemical Changes - are those in which different substances are formed - Ex.: burning rusting rusting decaying or spoiling decaying or spoiling acid reacting with metal acid reacting with metal

Chemical Changes - are those in which different substances are formed - Ex.: burning rusting rusting decaying or spoiling decaying or spoiling acid reacting with metal acid reacting with metal Physical change Ice changing to liquid waterWater breaking down into hydrogen and oxygen gases Chemical change

Signs of a chemical change Heat gained or lost Heat gained or lost Production of a gas Production of a gas Formation of a precipitate Formation of a precipitate Color change Color change

Methods of separating a mixture Use the different properties of the substances to separate them. Sand and iron filings Sand and iron filings Sand and salt Sand and salt Sand in water Sand in water Water from salt water Water from salt water Oil in water (immiscible liquids) Oil in water (immiscible liquids) Mixture of pigments Mixture of pigments filter Dissolve salt, evaporate water Remove iron with magnet Distill the water Settle and extract less dense liquid Paper chromatography

chromatography distillation

Substance – a homogeneous material consisting of one kind of matter Substance – a homogeneous material consisting of one kind of matter Compound – a substance that can be decomposed into simpler substances only by chemical means Compound – a substance that can be decomposed into simpler substances only by chemical means Element – substances that cannot be further broken down. Element – substances that cannot be further broken down. Organic substance contain carbon Organic substance contain carbon