Transcript Figure 2.8 Deflection of Cathode Rays by an Applied Electric Field

Ch 3. Molecules, Compounds, and
Chemical Equations
No change occurs inside a nucleus in chemistry
Atoms can lose or gain electrons
Na − e− → Na+
positive ion = cation
Mg − 2e− → Mg2+
Cl + e− → Cl−
O + 2e− → O2−
negative ion = anion
positive ions + negative ions
ionic compound
The attraction between positive ions and negative ions
is called ionic bond.
Green: Cl−, Purple: Na+
Atoms can combine together by sharing electrons
Covalent bond
Different elements combined by covalent bonds
Covalent compound
Molecule is a group of atoms held together by
covalent bonds.
Three kinds of chemical formulae to represent
a covalent compound
Molecular formula
Structural formula
Empirical formula
metals: tend to lose electrons
nonmetals: tend to gain electrons
metal + nonmetal → ionic compound
nonmetal + nonmetal → covalent compound
Row: period
Column: group
Elements in the same group have similar chemical
properties.
Remember these properties
Group 1A (alkali metals) form cations with ONE positive
charge.
Group 2A (alkaline earth metals) form cations with
TWO positive charge.
Group 7A (halogens) form anions with ONE negative
charge.
Group 8A (noble gases) usually do not form compounds.
Other common ions to remember:
Al3+, Zn2+, Ag+, Cd2+, Sc3+, O2−, S2−, P3−, N3−
Review Problem Set 2
How to write chemical formulae for ionic compounds?
1) Write positive ion first, then negative ion.
No “+” or “−” in a formula.
2) Subscripts are determined by balancing the charge.
number of positive charge = number of negative charge
3) When subscript is 1, no need to specify.
NOMENCLATURE
Ionic Compounds
Binary Ionic Compounds
two kinds of elements
Naming for Ions
Type I: fixed charge (remember them)
Cations
Type II: different charge
Naming for Ions
Type I: fixed charge (remember them)
Cations
Type II: different charge
Type I: Same name as the metal
Naming for Ions
Type I: fixed charge (remember them)
Cations
Type II: different charge
(mostly transition metals)
Naming for Ions
Type I: fixed charge (remember them)
Cations
Type II: different charge
(mostly transition metals)
Type I: Same name as the metal
Type II: Same name as the metal (charge in roman
number)
Naming for Ions
Cations: done
Anions: add –ide to element’s base name
Remember them
Naming for Ionic Compounds
Compound name = Cation name + Anion name
Exercises on Page 131
KF
PbI2
SrBr2
SnCl4
Mg3N2
SnO
Names → formulae
Calcium sulfide
Lithium nitride
Mercury (II) oxide
Aluminum chloride
Manganese (IV) oxide
Iron (III) oxide
NOMENCLATURE
Binary Ionic Compounds
Ionic Compounds with Polyatomic Ions
Naming for Ionic Compounds
Compound name = Cation name + Anion name
Exercises on Page 131
Ba(OH)2
CuNO2
NH4I
NaBrO4
Pb(C2H3O2)2
Problems Set 3
Naming of ionic compounds
1 mol = 6.022 x 1023 particles
mass in grams
molar mass 
moles
Unit: g/mol
molar mass and Avogadro’s number are exact numbers
CaCl2
a) Calculate the molar mass of CaCl2.
A sample of CaCl2 is 2.86 g.
b) How many moles of CaCl2 , Ca2+, and Cl−
are in this sample? How many Ca2+, and Cl−
ions are in this sample?
c) What is the mass of Ca2+ in this sample?
What is the mass of Cl− in this sample?
1 mol = 6.022 x
1023
particles
molar mass 
mass in grams
moles
Two ways to describe the composition of a compound
Chemical formula
Mass percent of each element
mass of component
mass percent 
 100 %
mass of whole sample
mass of component
mass percent 
 100 %
mass of whole sample
CaCl2
Calculate the mass percent of Ca and Cl.
Pick exactly 1 mol of compound to calculate mass percent.
molar mass 
mass in grams
moles
mass of component
mass percent 
 100 %
mass of whole sample
What is the mass percent of nitrogen in ammonium nitrate?
mass of component
mass percent 
 100 %
mass of whole sample
What is the mass percent of nitrogen in ammonium nitrate?
NH4NO3
Review Problem Set 3
NOMENCLATURE
Binary Ionic Compounds
Ionic Compounds with Polyatomic Ions
Binary Covalent Compounds
Remember these Prefixes
•
•
•
•
•
1 = mono2 = di3 = tri4 = tetra5 = penta-
•
•
•
•
•
6 = hexa7 = hepta8 = octa9 = nona10 = deca-
Binary Covalent Compounds
nonmetal-nonmetal
1. The first element in the formula is named first, using the
element name.
2. The second element is named as if it were an anion.
3. Prefixes are used to denote the number of atoms present.
4. The prefix mono- is never used for naming the first
element.
5. Drop the final o or a of the prefix when the element begins
with a vowel.
Examples: page 101-102, 131
NI3
PCl5
CO2
SnCl4
P4S10
a. phosphorus trichloride
b. chlorine monoxide
c. disulfur tetrafluoride
d. phosphorus pentafluoride
CO
H2O — water
NH3 — ammonia
NOMENCLATURE
Binary Ionic Compounds
Ionic Compounds with Polyatomic Ions
Binary Covalent Compounds
Acids
What is an acid?
An acid is a compound that releases hydrogen
ions (H+) when dissolved in water.
HCl → H+ + Cl−
HClO3 → H+ + ClO3−
dissolved in water = aqueous = aq
HCl(aq), HClO3(aq)
Binary acids: H and another element
Acids
Oxyacids: Anions (oxyanion) contain
an element and oxygen
HCl → H+ + Cl−
HClO3 → H+ + ClO3−
Binary Acids
General formula: HnXm
Rules:
Start with prefix: hydro
Use element root name of anion
Add -ic at the end
Add the word acid
Example: HF(aq), HCl(aq), HBr(aq), HI(aq), H2S(aq)
Oxyacids
General formula: HnXmOp
Rules:
Use base name of oxyanion, change
ending as follows:
change –ate to –ic;
change –ite to –ous.
Add the word acid
Use base name of oxyanion
change –ate to –ic;
change –ite to –ous.
Problems Set 4
Naming of compounds
Classification of Matter
Homogeneous (Solutions)
(visibly indistinguishable)
Mixtures
(multiple components)
Heterogeneous
(visibly distinguishable)
Matter
Elements
Pure Substances
(one component)
Ionic
Compounds
Covalent
Review Problem Set 4
1 mol = 6.022 x 1023 particles
mass in grams
molar mass 
moles
Unit: g/mol
molar mass and Avogadro’s number are exact numbers
N2O3 sample: 8.56 g
1 mol = 6.022 x 1023 particles
molar mass 
a)Calculate the molar mass of N2O3.
b)How many moles of N2O3 are in this sample?
c)How many moles of N are in this sample?
d)How many moles of O are in this sample?
e)How many N2O3 molecules are in this sample?
f)How many N atoms are in this sample?
g)How many O atoms are in this sample?
h)What is the mass percent of N in N2O3?
mass in grams
moles
Problem Set 5
Two ways to describe the composition of a compound
Chemical formula
Mass percent of each element
mass of component
mass percent 
 100 %
mass of whole sample
A laboratory analysis of a compound determined the following
mass percent: 30.45 % N and 69.55 % O.
What is its chemical formula?
mass in grams of element
molar mass of element 
moles of element
Pick exactly 100 g of compound to calculate.
A laboratory analysis of a compound determined the following
mass percent: 30.45 % N and 69.55 % O.
What is its chemical formula?
mass in grams of element
molar mass of element 
moles of element
Pick exactly 100 g of compound to calculate.
If the molar mass of this compound is 92.02 g/mol, what is
its molecular formula?
Review Problem Set 5
Example 3.18 on page 115
A laboratory analysis of aspirin determined the following mass
Percent: 60.00 % C, 4.48 % H and 35.52 % O.
What is its empirical formula?
mass in grams of element
molar mass of element 
moles of element
Pick exactly 100 g of compound to calculate.
If the molar mass of this compound is 180.154 g/mol, what is
its molecular formula?
Conversion to simplest integer ratio
1.000 : 2.002 : 2.998 = 1: 2 : 3
1.000 : 2.499 : 3.001 = 1: 2.5 : 3 = 10 : 25 : 30 = 2 : 5 : 6
1.0 : 2.4 : 3.0 = 10 : 24 : 30 = 5 : 12 : 15
In a chemical reaction,
Old chemical bonds are broken and new chemical bonds
are formed.
Atoms are neither created nor destroyed. Mass is conserved.
Example:
A−B + C−D → A−C + B−D
Chemical Equation:
Reactants → Products
CH4 + 2 O2 →
CO2
+ 2 H2O
Each chemical has a certain composition (formula).
We must balance each chemical equation.
CH4 + 2O2 → CO2
+
2H2O
CH4 + 2O2 → CO2
+
2H2O
Specify the physical states of the reactants and products
s — solid, l — liquid, g — gas, aq — in aqueous solution
CH4 (g) + 2O2 (g) → CO2 (g) + 2H2O (g)
How to balance a chemical equation?
1) Start from the most complicated chemical, adjust the
coefficients of others.
2) Make all coefficients to simplest integers.
Examples
C2H5OH (l) + O2 (g) → CO2 (g) + H2O (g)
C6H12O6 (s) + O2 (g) → CO2 (g) + H2O (g)
Fe2S3 (s) + HCl (aq) → FeCl3 (aq) + H2S (g)
NH3 (g) + O2 (g) → NO (g) + H2O (g)
Problem Set 6