Chapter 16- Elements of Chemistry Big Idea: ** Each atom has a sort of stickiness that enables it to connect to other atoms These groups of atoms are called ** Example: 1. Two atoms of hydrogen chemically combined with one atom of oxygen becomes water 2. Two atoms of hydrogen chemically combined with two atoms of oxygen becomes hydrogen peroxide- a disinfectant 16.1 Chemistry: the Central Science Chemistry – def. – ** Chemistry is considered the central science because it touches all other sciences. It springs from the principles of ** Serves as a foundation for the most complex science- ** It is also important as a backbone of ** Basic research- ** Applied research- ** 16-2 The Submicroscopic World Atoms are so small that a single grain of sand contains about 125 million trillion of them Some atoms link together to form larger but still incredibly small basic units of matter called ** Example: water – H2O – two atoms of hydrogen chemically combined with one atom of oxygen An 8-oz glass of water contains a trillion trillion water molecules Levels of magnification Macroscopic – matter large enough to be seen, measured and handled Microscopic- matter that is so fine that it can only be seen with a microscope Submicroscopic- the realm of atoms and molecules Phases of Matter Matter on this planet can exist in three phases- ** At the submicroscopic level, solid, liquid, and gaseous phases are distinguished by how the submicroscopic particles hold together. Solids Solid phase- ** Solids have definite volume and definite shape Liquids Liquid phase- ** Liquids have definite volume but no definite shape. Gases Gas phase- ** Gases have no definite volume and no definite shape Applying pressure to a gas squeezes the gas particles closer together, which decreases the volume. 16.3 Change of Phase In order to change the phase of a substance, you must either ** Melting – ** Freezing- ** Evaporating (evaporation)-** Condensing (condensation)- ** Subliming (sublimation)- ** The underlying cause of phase changes is always the ** Heat of fusion- ** For water, this is 334 J/g Heat of vaporization- ** For water, this is 2256 J/g- this is why you can briefly touch a wetted finger to a hot stove without harm 16.4 Physical and Chemical Properties Physical PropertiesDefinition- ** Chemical PropertiesDefinition- ** Physical Properties Physical Properties of a substance can change when conditions change without changing its chemical identity Cooling liquid water to below 00 C causes the water to change to solid ice. But it is still water, no matter what phase it is in. The only thing that changes is how the H2O molecules are arranged. This is an example of a physical change. Physical change Definition- ** These can be things like change in size, density, phase, etc. IMPORTANT NOTE: PHASE CHANGES ARE ALWAYS PHYSICAL CHANGES. Chemical Properties Definition- ** Examples: 1. Methane gas has a chemical property of reacting with oxygen to produce carbon dioxide and water along with appreciable heat. (how many heat their homes) 2. Copper has a chemical property of reacting with carbon dioxide and water to produce a new greenish-blue solid known a patina. (why copper statues turn green) 3.Gold does not react with acid but iron does. Chemical Change During a chemical change, there is a change in the way the atoms are chemically bonded to one another A ** is the force of attraction between two atoms that holds them together So a chemical change is any change in a substance that involves a rearrangement of the way the atoms are bonded Chemical Reaction We call chemical changes- reactions So a chemical change means the same thing as a chemical reaction During a chemical reaction, new materials are formed by a change in the way atoms are bonded together. 16.5 Determining Physical and Chemical Changes After a**, the molecules are the same ones you started with. Water vapor (gas) is still H2O even after the liquid water has boiled into the vapor. After a **, the original molecules have been taken apart and new molecules are in their place. Chemically reacting iron with oxygen makes a new substance – rust which is reddish brown instead of silver. How to tell if a chemcial or physical reaction has taken place Guidelines: In a physical change, a change of appearance is the result of a new set of conditions imposed on the same material. Restoring the original conditions restores the original appearance Frozen water melts on warming In a chemical change, a change in appearance is the result of the formation of a new material that has its own unique set of physical properties. Look for evidence of different properties Iron is a material used to build cars. Rust is not. 16.6 the Periodic Table The ** is a listing of all the known elements with their atomic masses, atomic numbers and atomic symbols. Most of the known elements are metals Metals are elements that are shiny, opaque and good conductors of heat and electricity Metals are malleable, which means they can be hammered into different shapes or bent without breaking Metals are ductile, which means they can be drawn into wires. More on metals All but a few metals are solid at room temperature Exceptions: Mercury (Hg) is a liquid at 250 C (770 F) Gallium (Ga), Cesium (Cs) and Francium (Fr) will become liquids at 300 C (860 F) Another notable exception: Hydrogen (H) which normally behaves like a nonmetallic gas will take on the properties of a liquid metal at very high pressures Metals can be found to the left of the zigzag line and takes up 2/3 of the periodic table Nonmetals Located at the far right side of the periodic table (with the exception of hydrogen)- to the right of the zigzag line Nonmetals are very poor conductors of electricity and heat and may be transparent Solid nonmetals are not malleable or ductile They are brittle and shatter when hammered At 300 C some are solids- carbon (C), other are liquid – bromine (Br) and still others are gases- helium (He) Metalloids Six elements are classified as metalloids – these are situated between the metals and nonmetals and have both metallic and nonmetallic properties Boron (B) Germanium (Ge) Silicon (Si) Arsenic (As) Antimony (Sb) Tellurium (Te) Mrs.Semmler’s note: aluminum (Al) is also considered a metalloid by some, as are Polonium (Po) and Astatine (At)- you are safe if you identify metalloids as bridging the zigzag line. More on metalloids Example of both characteristics: silicon is used in computer circuits and power strips as it will only conduct electricity at certain temperatures. If the temperature of the circuit gets too high, the silicon chips in the circuit will shut down until the temperature lowers. This semi-conductor property keeps appliances and computers from becoming damaged during power surges. ** note: Germanium would make a better semi-conductor than silicon (it is located closer to the metals) but silicon is much more abundant (hence cheaper) Periods and Groups Horizontal rows – Periods The properties of elements gradually change as you move across a period This is called a periodic trend One example of a periodic trend is that the size of atoms increases as you move from the lower left to the upper right corners of the table Another important periodic trend is how easily atoms lose electrons- some atoms hold on to their electrons tightly- others give them away readily. Atoms on the lower left side of the table lose electrons easily. For atoms to the upper right, however, losing electrons is difficult. Vertical Columns- Groups (sometimes also called Families) Down any group, the properties of elements tend to be similar (so they are said to be ‘grouped’ or ‘in the same family’) Group names Some of these groups have special names- read pgs 318 and 319 to find out more Group 1 – alkali metals Group 2 – alkaline earth metals Group 16 – chalcogens Group 17- halogens Group 18- noble gases- unreactive gases Transition metals Elements of groups 3 through 12 are called transition metals because of their central location Tend to be harder than the alkali metals and less reactive with water so they are used for structural purposes Most notable transition metals- iron (Fe), copper (Cu), nickel (Ni), chromium (Cr), silver (Ag) and gold (Au) Lesser known but important for their non-corrosive properties are titanium (Ti), molybdenum (Mo) and manganese (Mn) – used in implant devices for things like hip replacements. Inner Transition Metals Lanthanide series – atomic numbers 58 to 71 Similar physical and chemical properties Tend to be found in the same locations on earth Difficult to purify Some lanthanide elements are used in the fabrication of light-emitting diodes (LEDs) of computer monitors and flat-screen TVs. Actinide series – atomic numbers 90 to 103- although elements heavier than uranium are not found naturally on the planet but are synthesized in laboratories (man-made) Likewise have similar properties and are difficult to purify Causes a problem for the nuclear power industry that requires purified samples of uranium (U) and plutonium (Pu) 16.7 Elements to Compounds Element is generally used an entire macroscopic or microscopic sample. Atom is used when talking about the submicroscopic particles in a sample. Example- gold is an element that is made up of gold atoms The fundamental unit of an element is indicated by its elemental formula. For most elements the fundamental unit is made up of one atom; others can form molecules Gold exists in single atom units for the fundamental unit is Au. Seven elements (diatomic elements) can only be found in pairs: N2, O2, H2, F2, Cl2, Br2, I2 Compounds When atoms of different elements bond to one another, they form compounds. A compound is represented by a chemical formula Example: sodium atoms and chlorine atoms bond to form the compound sodium chloride, NaCl Nitrogen atoms and hydrogen atoms bond to form the compound ammonia, NH3 Subscripts (the small lowered numbers) indicate the ratio in which the atoms combine (there is one nitrogen atom for every three hydrogen atoms) Note: if there is only one atom, we don’t use the number ‘1’. Other examples Naming Compounds To name compounds, there are some questions you must answer about the compound. Your answer will determine how the compound is named. Is the compound only two elements – a metal and a non-metal? Use guideline 1 Or is the compound only two elements – two non-metals? Use guideline 2 Or, is the compound made up of more than two elements? Use guideline 3 Guideline 1 – metal/non-metal binary(two element) compounds The first element retains its elemental name The second element adds an –ide ending to its root name NaCl – sodium chloride (was chlorine) CaF2 – calcium fluoride (was fluorine) Li2O – lithium oxide (was oxygen) Sr3P2 – strontium phosphide (was phosphorus) Metal/nonmetal compounds using metals that can form more than one charge Some atoms can form ions that can have more than one charge Ex- Fe (iron) can form two types of ions Fe +2 or Fe+3 Cu (copper) can form two types of ions Cu+2 or Cu+1 These metals require a roman numeral denoting the charge of the ion used FeS – iron (II) sulfide Fe2S3 – iron (III) sulfide CuO – copper (II) oxide Cu2O – copper (I) oxide Guideline 2 – 2 non-metal compounds The first element retains its elemental name The second element adds an –ide ending to its root name Both elements get prefixes indicating how many of each are in the compound Commonly used prefixes 1 – mono 2 – di 3- tri 4- tetra 5- penta 6- hexa 7- hepta 8- octa 9 – nona 10- deca Examples Note: don’t use mono for the first element Also- O-O combination drop one of the O’s A-O combination drop the O CO – carbon monoxide (not monocarbon monooxide) N2O4 – dinitrogen tetroxide (not dinitrogen tetraoxide) N2P4 – dinitrogen tetraphosphide Guideline 3- compounds made up of more than two elements The compound will contain a polyatomic ion Polyatomic ions are groups of elements that have a charge and special names that are used. Follow the general rules for naming (either using the elemental name for the first element or changing second element name to an –ide ending for the second element) and use the polyatomic ion name Polyatomic ions Examples SO4+2 – sulfate NH4+1 – ammonium NO3-1 – nitrate NO2-1 - nitrite CO3-2 - carbonate Compounds that contain polyatomic ions NaSO4 – sodium sulfate FeSO4 – iron (II) sulfate NH4O – ammonium oxide NH4OH – ammonium hydroxide Cu2CO3 - copper (I) carbonate