9 Chapter Chemical Reactions Compounds and Elements Matter: Anything that has mass and occupies space Matter can be divided into: Pure Substance Divided into two Compounds i.e.: pure water, salt, sugar, etc.
elements hydrogen, oxygen, carbon, etc.
Qualities Fixed, definite composition throughout
Compound: can be down by chemical means to give simpler substances (H20 H and O). Elements are a pure substance that cannot be broken down to get simpler substances; theyre fundamental. Mixture Divided into two Homogeneous Uniform properties throughout
Solutions, alloys, salt in water, dissolved substances Heterogeneous Not the same throughout, sample not
uniform
water, coal throughout What is a mixture?
i.e.: oil and water, sand and properties are not uniform
Combination of two or more substances with 3 or more properties Must be separated by simple physical means property Of variable composition Each component must retain its Class is a mixture of boys
and girls
Doesnt depend on number of boys/girls Separated by simple means (boys go left, girls right) Even though mixture, boys are boys, girls are girls
Physical and Chemical Changes
Physical change does not result in the change of that substance or lead to a new compound. No change in identity of matter. i.e. : melt ice to water, boil water)
Chemical change results in the change of the identity of the matter that produces new substances i.e.: burning, cooking, spoiling food
Atoms and Molecules A molecule is the smallest part of a compound or
H20 is the molecule for water. Molecules of the same element can also be Na or 02 or 03 as groups or singular atoms. Atom is the smallest particle of an element
Chemical Reactions
Chemical Reactions are reactions that result in the creation of different chemical substances by forming or breaking chemical bonds Chemical Energy internal bonding potential energy Chemical Equations is a symbolic summary of chemical reactions
Valence Electrons and Ions Electrons in the outermost shell Determine the chemical properties and reactions of all elements
Octet Rule: Atoms gain, share or lose electrons to acquire an outer shell of eight electrons except Hydrogen (which requires 2) e.g. Sodium (Na) and Chlorine (Cl)
Chemical Bonds Electrostatic attractions that pull atoms together in compounds Three Types
Ionic Bond: Na+ and Cl- is a bond between metals and non-metals. It is the transfer of electrons. Na transfers and electron to Cl, so it is Na+ and Cl- to get NaCl Electrostaic force = bonding force
Form crystalline solids with orderly geometric structure. All are soluble in water, usually are white
Covalent Bonds: Sharring a pair of electrons. Ie: H2. H- and H- Share the electrons to get to the p sublevel of 2
Octets achieved through sharing of electron pairs between nonmetallic elements, e.g HCl Metallic Bonds: Outer electrons move freely throughout metal Electron Gas electrons move freely around the element. Hence metals are good conductors of heat and electricity e.g. copper. Energy and electrons in ionic bonding Reaction energy released = heat of formation Number of electrons lost must equal number of electrons gained. i.e. Na + Cl = Na+CL- + 2E
Energy of formation is the energy from fussion and bonding where the electrons are released or changed Ionic compounds and formulas Formulas must be electrically neutral Formulas List the type and number of atoms in a compound
The number of each atom is decided by electrons gained/ost/shared Things to note IA will have + 1 ion IIA will have +2 ion will Aluminum form +3 ion VIA gain 2e to form -2 ion VII gain 1e to form -1 ion All positive ions are CATIONS All negative ions are ANIONS
Always write the metal first
Covalent Bonds Sharing of electrons attraction ClH Chlorine now has 8 electrons when bonded, H has 2 Chemical bonds formed by sharing pairs of electrons Electrons shared to form octets, ideally (Hydrogen gets 2) Overlap of shared electron clouds between nuclei yields net
Identical atoms within covalent compounds are electrically neutral but non-identical atoms are not neutral H2 and HCl Covalent compounds and formulas Electron dot representation Bonding pairs shared Lone (non-bonding) pairs not shared.
Multiple Bonds Check notes
Composition of compounds Million of different combinations of over 90 elements Common names based on use Covalent compounds and Molecular compounds are the same Different for ionic and covalent compounds
One common rule ,,ide means compound contains only two different element ion) Use subscripts to make the compound electrically neutral Ionic Compound formulas and Names Write the metal before the non-metal (positive ion then negative
nonmetal
Name the cation first and add ide to the stem name of the
No matter what the number of atoms at the end or beginning, its just ,,ide and not "tri" and "di" thats only for covalent naming. i.e. NaCl Sodium Chlroide i.e. BeCl2 Beryllium Chloride
Covalent compound formulas and names
Name the first element in the compound first and use Greek prefix to indicate number of atoms present Add "ide" (for a 2 element compound) to the stem name of the second element and use Greek prefix to indicate the number of atoms present Mono, di, tri, tetra, penta... We can often ignore "mono" as its understood
Problem name the following: HCl Hydrogen Chloride H2S Dihydrogen Sulfide CH4 Carbon tetrahydride
Chemical Equations Reactants Yield Products (A + B = C) Represents chemical reactions using chemical symbols Rules Use chemical symbols and formulas for each reactant and The coefficient multiplies everything in the formula All elements on reactants side are also on product side
product
Equal numbers of atoms of each element on reactant side as on product side
Types of Chemical Reactions Oxidation Reduction (Redux) Reaction in which electrons are transferred from one atom E.g. Zn + Cu2+ = Zn2+ + Cu
to another
Copper is being reduced by Zinc, so Zinc, donating the electrons, is the reducing agent. Copper is gaining two electrons, so it goes from +2 to 0 charge. Copper gains the electrons and is oxidizing Zinc, by changing the charge of Zinc. The REDUCING AGENT is OXYDIZED, and the OXYDIZING AGENT is REDUCED. Combination Reaction
Synthesis in which two or more substances combine to form a single compound or both Opposite of combination E.g. 2Na + Cl2 =2 NaCl
Decomposition Reaction Compound broken down into elemtns, simpler compounds
Replacement Reaction E.g. Zn + CuCl2 = ZnCl2 + Cu (This is both replacement and redux reaction) We have only one salt and metal
Ion Exchange Reaction E.g. AgNo3 + NaCl = AgCl + NaNO3
We have TWO salts where ions are exchanged, as opposed to Replacement where ONE ion is exchanged We have exchanged Ions
Ions of one compound interact with ions of another to form either a precipitate, gas or water. Writing Assignment (Due 11/19/2007) Title Name Course Introduction Discussion Influence on Society Your Views what do I think? References Acknowledgments (say thank you parents) General Organization