Presentation on theme: "Past to Present. Aristotle: Four Element Theory theory lasted for about 2000 years. not a scientific theory because it couldnt be tested against observation."— Presentation transcript:
Past to Present
Aristotle: Four Element Theory theory lasted for about 2000 years. not a scientific theory because it couldnt be tested against observation
Democritus In 300 BC, Democritus said atoms were indivisible particles. His theories were the first mention of atoms (atomos). Not a testable theory, but a conceptual model. no mention of any atomic nucleus or its constituents. cannot be used to explain chemical reactions
Lavoisier (late 1700s) law of conservation of mass (the mass of substances produced from a chemical reaction is always equal to the mass of the reactants.) law of definite proportions (Ex. water is always 11% hydrogen and 89% oxygen)
Proust (1799) if a compound is broken down into its constituents, the products exist in the same ratio as in the compound. experimentally proved by Lavoisier laws.
Dalton (early 1800s) atoms are solid, indestructible spheres (like billiard balls) provides for different elements (these would be different spheres) based on the Law of Conservation of Mass having a molecule (atoms combine in simple whole number ratios) explains the law of constant composition
JJ Thompson (1850s) raisin bun model solid, positive spheres, with negative particles embedded in them 1st atomic theory to include protons (+) and electrons (-)
Rutherford (1905) showed that atoms have a positive, dense center with electrons outside it. resulted in planetary model explains why electrons spin around nucleus suggests atoms are mostly empty space
Bohrs Theory electrons exist in outer shells of an atom when electrons absorb energy > they move to a higher orbital or shell when electrons release energy as a photon of light > they fall from a higher shell to a lower one Bohr based his model of the energy or light emitted by different atoms
each atom has a different spectra of light each element has a set of lines which represents a photon of light emitted from the atom
prisms separate white light into colours AS WELL: matter emits light when its heated light travels as protons the energy photons carry depends on their wavelength
Physical Separations do not involve chemical reactions classified as Mechanical (uses gravity, contact forces or motion) or Non-mechanical (uses heat, magnetism, electricity, dissolving) Decanting (sedimentation): carefully pour off liquid and leave sediment Centrifugation: spinning to enhance density separation
Chromatography: a flowing liquid or gas (mobile phase) carries substances at different rates through a stationary phase, e.g. gas chromatography, paper chromatography Filtration: separation based on particle size
Electrophoresis: electric current used to separate particles by surface charge
Distillation: a mixture of liquids is heated until components vaporize. The gas is then condensed back into liquid form and collected; uses difference in BP to separate mixture
Other examples: evaporation, magnetic separation, reverse osmosis, sifting, skimming Recrystallization: rock candy!
Binary Compounds A binary compound contains the atoms of only two different elements, and a binary ionic compound contains only two types of monatomic ions (charged atoms), e.g. NaCl. Cation: positively charged ion (Trick: think of t in cation as +), e.g. Pb 4+ Anion: negatively charged ion, e.g. S 2- ***The name of any IONIC COMPOUND is the name of its metal ion followed by the name of its non-metal ion, e.g. sodium chloride.***
PbS 2 Compounds always have a net charge of 0. They are always neutral. the charges of the ions making up a compound must negate each other (cancel each other out)! 2Al 3+ (aq) + 3S 2- (aq) Al 2 S 3 (s) 2(3+) 3(2-) Try It: Pb 4+ and S 2- combine to make ______________ Note: reduce to lowest terms!
Ion charge of elements depends on group number (column). Elements not included have more than one ion configuration.
Multivalent Ions Multivalent elements have more than one way of arranging their outer (valence) electrons. They have more than one stable ion form. e.g. Fe 2+ and Fe 3+ are known as iron(II) and iron(III) ions The roman numeral in brackets corresponds to the charge on the ion and is pronounced as the number it represents, i.e. iron(II) is pronounced iron two.
Example 1: What is the formula for tin(IV) sulphide? Example 2: What is the name of Fe 2 S 3 ? 1. Write the symbols of the ions used. Sn 4+ S Combine the ions in the simplest ratio that results in their charges cancelling. Sn S 2- SnS 2 1. Write the names of the two constituent ions. iron(II) or iron(III), sulphide 2. Write the formulas of the possible compounds to see which has the correct formula. Fe 2+ + S 2- FeS 2Fe S 2- Fe 2 S 3 Iron(III) oxide!
Do p. 98 Practice Problems Solutions 1a) Li 2 Sc) AlCl 3 e) SnI 2 b) Cr 2 O 3 d) PbSf) ZnBr 2 2a) zinc oxided) sodium iodide b) lead(IV) chloridee) potassium sulfide c) copper(II) chloridef) chromium(II) oxide
Polyatomic Ions Polyatomic ion: a charged group of covalently bonded atoms (similar to a molecule but with a charge). Relatively stable, often remain intact in chemical reactions Many are oxyanions: an atom of one element bonded to some number of oxygen atoms. E.g. nitrite NO 2 - nitrate NO 3 - sulfite SO 3 2- sulfate SO 4 2- lesser number of O atoms takes the –ite suffix greater numer of O atoms takes the –ate suffix
More than two oxyanions in a series, e.g. ClO - hypochlorite (hypo- meaning less than) ClO 2 - chlorite ClO 3 - chlorate ClO 4 - perchlorate (per- meaning more than) The prefix bi- before the name of a polyatomic ion indicates an H+ was added to it, e.g. CO 3 2- carbonate ion becomes HCO 3 - bicarbonate ion (hydrogen carbonate)
Exceptions: OH - is hydroxide (only polyatomic ion with the –ide suffix) Cr 2 O 7 2- is called dichromate ion Most polyatomic ions we will encounter are anions (negatively charged) with the exception of ammonium, NH 4 + A table of polyatomic ions will be provided to you. Polyatomic ions are bracketed in ionic compounds
Example 1: What is the formula of potassium sulphite? Example 2: What is the name of Cr(HSO 4 ) 2 ? 1. Write symbols of ions named. K + SO Combine ions in the simplest ratio that results in their charges cancelling. 2 K + + SO 3 2- K 2 SO Write the names of the two ions. Chromium(II) or chromium(III) and bisulphate 2. Write the formulas of the possible compounds to see which has the correct formula. Chromium(II) bisulphate Cr HSO 4 - Cr(HSO 4 ) 2 or chromium(III) bisulphate Cr HSO 4 - Cr(HSO 4 ) 3
Do Practice Problems, p. 100, 1-2 1a) BaSO 4 d) Sn(C 2 O 4 ) 2 b) AgNO 3 e) Al 2 (Cr 2 O 7 ) 3 c) HgBr 2 f) KF 2a) zinc hydroxided) sodium acetate b) tin(II) oxidee) magnesium iodide c) copper(II) hypochlorite f) iron(II) dichromate
Binary Molecular Compounds Molecular compounds are made up of two non-metal atoms which share electrons to become stable compounds. The names of all binary compounds have an –ide suffix. Prefixes are used to indicate the number of atoms. The term mono- is understood but not used for the first element in the pair, e.g. CO 2 is carbon dioxide, not monocarbon dioxide.
Prefixes for Molecular Compounds NumberPrefix 1mono- 2di- 3tri- 4tetra- 5penta- 6hexa- 7hepta- 8octa- 9nona- 10deca- Example: What is the formula for xenon tetrafluoride? Example: What is the name of P 4 S 10 ? XeF4 4 phosphorous and 10 sulphur, so… tetraphosphorous decasulphide.
Do Practice Problems on p a) NOc) N 2 O 4 b) NO 2 d) N 2 O 3 2a) phosphorous pentachloride b) sulphur dioxide c) carbon monoxide d) diphosphorous pentaoxide
Hydrates When many salts crystallize out of aqueous solution they incorporate water molecules in a fixed ratio and pattern into their ionic crystal lattice. These are called hydrates. Since most salts are destined to be dissolved in water, this does not present a problem. Water is an integral part of the hydrate, so it must be accounted for in the name. We use the prefixes for molecular compounds combined with the term – hydrate to indicate the number of associated water molecules.
Gently warming a hydrated salt will remove the associated water from the crystal. Anhydrous refers to the salt without the water. Dessicants are anhydrous salts that can absorb water from the air (hygroscopic) to form hydrates. They are used to… Keep moisture out of dried foods, e.g. beef jerky Dry flowers for crafts, e.g. silica salt beads (silica gel) Keep running shoes, guitars, etc. dry in their boxes before they are purchased
Crystals of CuSO 4 ·5H 2 O Anhydrous CuSO 4 powder
Example 1: What is the formula for copper(II) sulphate heptahydrate? Example 2: What is the name of NaCH 3 COO, 3H 2 O? 1. Write the symbols of the ions named.Cu 2+ SO Combine the ions in the simplest ratio that results in the charges cancelling. Cu 2+ + SO 4 2- CuSO 4 3. Tack on the appropriate number of water molecules to complete the formula. heptahydrate means 7H 2 O CuSO 4 7H 2 O 1. Write the names of the two constituent ions.sodium, acetate 2. Tack on the appropriate number of water molecules using the prefix code (–hydrate). sodium acetate trihydrate
Do practice problems on page a) BaCl 2, 2H 2 Ob) Na 2 CO 3, H 2 O c) Fe(NO 3 ) 3, 9H 2 Od) Ba(OH) 2, 8H 2 O 2a) cobalt chloride hexahydrate b) iron(III) chloride tetrahydrate c) sodium dichromate dihydrate d) magnesium sulphate heptahydrate
Acids Acids are a special type of molecular compound that can be induced to form ions. Their names are based on the name of the anion formed and whether it contains oxygen. Acids can be thought of as one or more H + ions bonded to an anion.
No oxygen: prefix hydro- precedes the name of the ion and the suffix –ic replaces the –ide in the anions name hydro_________ic acid Contains oxygen: suffix –ic replaces –ate in the ions name or the suffix –ous replaces –ite e.g. hydrogen sulphate is sulfuric acid and hydrogen sulphite is sulphurous acid
Note: The term acid can refer to the compound or to its solution. H 2 SO 4 (l) and H 2 SO 4 (aq) are both called sulphuric acid
Example 1: What is the formula for hydrobromic acid? Example 2: What is the name of HNO 2 ? 1) Decode the suffix to determine possible anions: bromic denotes bromide or bromate. Br - or BrO 3 - 2) Decode the prefix (if any) to select the anion: hydro- indicates that the anion does not contain oxygen. Br - 3) Determine the formula from the ion charges.H + + Br - HBr 1) Write the names of the two constituent ions.hydrogen nitrite 2) Use the code for naming acids. The anion contains oxygen, so the suffix –ous replaces –ite in the anions name. nitrous acid
Test on Oct. 23, 2012 Do Practice Problems on page a) HFlb) HClOc) H 3 PO 4 d) H 2 S 2a) acetic acidc) carbonic acid b) sulphurous acidd) hydroiodic acid Complete the Review questions on p Study questions from p , p , p