CHM - Lecture 3 PDF

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Tuesday, August 28, 2018

Chemistry Lecture 3!

- Formulas and Names of Ionic Compounds ! 1. positive ion always first in formula ! 2. subscripts must produce a neutral formula unit! 3. subscripts should be smaller set of whole numbers possible !

- Ionic Compounds ! • look for a metal! • look for NH4! • learn polyatomic formulas and charges !

- Molecular Compounds ! • non metals (2 or more) ! - H, N, O, halogens ! - P, S, Se, Te! - C, Si, B, As! • when non metals combine, they form molecules ! • multiple forms: ! - simple: CO2, NO, PCl3! - complex: C3H6O! • organic ! • biochemical ! 1

Tuesday, August 28, 2018

- Binary Molecular Compounds between 2 Nonmetals • first word: name of the element that is first in formula ! • second word: name of stem of second element with ending -ide • specify the number of each atom by way of a prefix !

• examples:

CO - carbon monoxide. Co2 carbon dioxide!

BCl3 boron tricloride! SO3 sulfur trioxide! NO nitrogen monoxide! N2O4 dinitrogen (II) tetroxide !

- Getting the formula from the name ! - bromine triflourine ! - BF3! - selenium dioxide ! • SeO2! - Silicon hexabromide ! • SiBr6! - Diphosphourous pentoxide ! • P2O5!

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- The mole ! • is the unit we use to COUNT “things” ! • it’s a big number! • use it to count really small atoms! • 1 mole of things = 6.022x10^23. ! - Particles and the Mole ! • avogadro’s number of particle in a mole of substance !

- Mole ! • one mole is the amount of substance that contains as many particles as there are in 12.0 g of 12C. !

• 1 mol = 12g/mol ! • 1 mol of oxygen = 16 g/mol ! • how many atoms of carbon in 1 mol of carbon? 6.02 x10^23 ! - Molecular weight vs Molecular mass ! Water - ! H20 !

- 2H +1O! - 2*(1) +(16)! - = 18 g/mol ! 3

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- Aspirin ! - C9H8O4! - 9*(12)+8(1)+4(16)! - =108+8+64 = 180g/mol ! -NaHCO3! $

- 23+1+12+16+16+16 = 84!

• molecular weight ! - mass of 1 molecule in amu ! • molar mass ! - mass of 1 mole in grams - Mass-Mole Conversion ! • 1 mole = molar mass in grams! - atoms (Atomic wright or mass)! - molecular (molecular weight or mass)! - ionic compounds !

Lecture Example: ! 4

Tuesday, August 28, 2018 $

how many magnesium atoms are there in 150.0 g of magnesium? !

$

how many grams of chromium are there in 25.1g of choromium (III) acetate?!

- Percentage composition! • calculate the mass percent (weight percent) of each element in a compound ! • strategy ! • (atoms of an element)*(atomic weight)! _______________________________________________ * 100%! $

(formula weight of compound)!

Lecture Example 1: ! $

what is the % composition of Ca(OH)2?!

(atoms of an element)*(atomic weight)! _______________________________________________ * 100%! $

(formula weight of compound)!

Lecture Example 2: ! $

what is the % composition of Ca(OH)2?!

(atoms of an element)*(atomic weight)! _______________________________________________ * 100%! $

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(formula weight of compound)!

Tuesday, August 28, 2018 Lecture Example 3: ! $

what is the % composition of Ca(OH)2?!

(atoms of an element)*(atomic weight)! _______________________________________________ * 100%! $

(formula weight of compound)!

it is important when using the term “mole” that a mole has the same number of atoms for all elements. ! Take Home “research problem” !

- Percentage Composition ! • analysis used to characterize unknown compounds ! - percent composition data can be used to calculate an empirical formula

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- Empirical vs Molecular Formula ! • empirical ! - only shows the simplest ratio of atoms in the formula ! - almost all ionic compounds are represented by this formula ! • Lecture Example: !

- a compound is found to be 64.82% carbon, 21.59% oxygen and 13.59% hydrogen. What is the empirical formula for this compound?! 7

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• molecular !

- show the actual composition of a molecule ! - determining the molecular formula ! - for some compounds, the molecular formula is the same or a multiple of the empirical formula!

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- since the molecular formula is multiple is scaled by a factor “n”! - the molecular and empirical molar masses must also scale by the same ratio! $

molar formula mass (g/mol) !

_______________________________________ =n! $

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empirical formula mass (g/mol)...