Transcript Document

Do Elements exist?
Periodicity
When one looks at the chemical properties of
elements, one notices a repeating pattern of
reactivity.
Noble Gas
Halogen
Group
Alkali Metal
Alkali Earth Metal
Period
2.4
Periodic Table
Nonmetals are on the right side of the periodic
table (with the exception of H).
Periodic Table
Metalloids border the stair-step line (with the
exception of Al and Po).
Periodic Table
Metals are on the left side of the chart.
A molecule is an aggregate of two or more
nonmetals in a definite arrangement held
together by chemical bonds
H2
H2O
NH3
CH4
A diatomic molecule contains only two atoms
H2, N2, O2, Br2, HCl, CO
A polyatomic molecule contains more than
two atoms
O3, H2O, NH3, CH4
2.5
A molecular formula shows the exact number of
atoms of each element in the individual molecules
which are held together by weak attractive forces.
An empirical formula shows the simplest
whole-number ratio of the atoms in a substance
molecular
empirical
H2O
H2O
C6H12O6
CH2O
O3
O
N2H4
NH2
2.6
Diatomic Molecules
These seven elements occur naturally as
molecules containing two atoms.
A molecule as we saw in a previous slide.
How can we name these? Remember the
Law of multiple proportions.
H2
H2O
NH3
CH4
H2, N2, O2, Br2, HCl, CO
2.5
Nomenclature of Binary Molecular
Compounds
• The lowest or most to the
left atom is usually listed
first.
• A prefix is used to denote
the number of atoms of
each element in the
compound (mono- is not
used on the first element
listed.)
Nomenclature of Binary
Compounds
• The ending is changed to ide.
– CO2: carbon dioxide
– CCl4: carbon tetrachloride
Nomenclature of Binary Compounds
If the prefix ends with a or
o and the name of the
element begins with a
vowel, the two successive
vowels are often
condensed:
N2O5: dinitrogen pentoxide
Molecular Compounds
HI
hydrogen iodide
NF3
nitrogen trifluoride
SO2
sulfur dioxide
N2Cl4
dinitrogen tetrachloride
NO2
nitrogen dioxide
N2O
dinitrogen monoxide
TOXIC!
Laughing Gas
2.7
An ion is an atom, or group of atoms, that has a net
positive or negative charge.
cation – ion with a positive charge
If a neutral atom loses one or more electrons
it becomes a cation.
Na
11 protons
11 electrons
Na+
11 protons
10 electrons
anion – ion with a negative charge
If a neutral atom gains one or more electrons
it becomes an anion.
Cl
17 protons
17 electrons
Cl-
17 protons
18 electrons
2.5
Common Cations
Common Anions
Patterns in Oxyanion Nomenclature
• When there are two oxyanions involving the
same element:
– The one with fewer oxygens ends in -ite
• NO2− : nitrite; SO32− : sulfite
– The one with more oxygens ends in -ate
• NO3− : nitrate; SO42− : sulfate
A monatomic ion contains only one atom
Na+, Cl-, Ca2+, O2-, Al3+, N3-
A polyatomic ion contains more than one atom
OH-, CN-, NH4+, NO3-
2.5
Do You Understand Ions?
+
27
3
How many protons and electrons are in 13 Al ?
13 protons, 10 (13 – 3) electrons
2- ?
Se
How many protons and electrons are in 78
34
34 protons, 36 (34 + 2) electrons
2.5
“Always Ions”
Zn2+
Ag+
• When atoms lose or gain electrons, they become
ions.
– Cations are positive and are formed by metals.
– Anions are negative and are formed by nonmetals.
– Some elements only have one stable ionic state!
ionic compounds consist of a combination of cations
and an anions
• the formula is reported as an empirical formula
• the sum of the charges on the cation(s) and anion(s) in each
formula unit must equal zero
The ionic compound NaCl
2.6
Writing Formulas
• Because compounds are electrically neutral, one
can determine the formula of a compound this
way:
– The charge on the cation becomes the subscript on the
anion.
– The charge on the anion becomes the subscript on the
cation.
– If these subscripts are not in the lowest whole-number
ratio, divide them by the greatest common factor.
Formula of Ionic Compounds
2 x +3 = +6
3 x -2 = -6
Al2O3
Al3+
1 x +2 = +2
Ca2+
1 x +2 = +2
Na+
O22 x -1 = -2
CaBr2
Br1 x -2 = -2
Na2CO3
CO322.6
Inorganic Nomenclature
• Write the name of the cation.
• If the anion is an monoatomic ion, change
its ending to -ide; if the anion is a
polyatomic ion … do you want to memorize
400+ of these?
• If the cation can have more than one
possible charge, write the charge as a
Roman numeral in parentheses.
Inorganic Nomenclature
Link to Activity
Acid Nomenclature
• An anion with H+.
• If the anion in the acid ends in -ide, change the
ending to -ic acid and add the prefix hydro- :
– HCl: hydrochloric acid
– HBr: hydrobromic acid
– HI: hydroiodic acid
Acid Nomenclature
• An anion with H+.
• If the anion in the acid ends in -ite, change the
ending to -ous acid:
– HClO: hypochlorous acid
– HClO2: chlorous acid
Acid Nomenclature
• An anion with H+.
• If the anion in the acid ends in -ate, change the
ending to -ic acid:
– HClO3: chloric acid
– HClO4: perchloric acid
Polyatomic Ions Revisited
ammonium
SO4
2-
sulfate
CO32-
carbonate
SO32-
sulfite
HCO3-
bicarbonate
NO3-
nitrate
-
nitrite
-
NH4
+
ClO3
-
Cr2O7
2-
CrO42-
chlorate
NO2
dichromate
SCN
thiocyanate
chromate
OH-
hydroxide
Note: These names have meaning and can
be “calculated.”
2.7
Oxidation Number or State
The charge the atom would have in a compound if
electrons were completely transferred.
Electron Book Keeping Method.
1. Free elements in their standard state have an
oxidation number of zero.
Na, Be, K, Pb, H2, O2, P4 = 0
2. In monatomic ions, the oxidation number is equal to
the charge on the ion.
Li+, Li = +1; Fe3+, Fe = +3; O2-, O = -2
3. The oxidation number of oxygen is usually –2. In H2O2
and O22- it is –1.
4.4
4. The oxidation number of hydrogen is +1 except when
it is bonded to metals in binary compounds. In these
cases, its oxidation number is –1.
5. Group IA metals are +1, IIA metals are +2 and fluorine is
always –1.
6. The sum of the oxidation numbers of all the atoms in a
molecule or ion is equal to the charge on the
molecule or ion.
HCO3Oxidation numbers of all
the elements in HCO3- ?
O = -2
H = +1
3x(-2) + 1 + ? = -1
C = +4
4.4
IF7
Oxidation numbers of all
the elements in the
following ?
F = -1
7x(-1) + ? = 0
I = +7
NaIO3
Na = +1 O = -2
3x(-2) + 1 + ? = 0
I = +5
K2Cr2O7
O = -2
K = +1
7x(-2) + 2x(+1) + 2x(?) = 0
Cr = +6
4.4
Do You Understand Oxidation State?
What is the oxidation state of Sulfur in Sulfate?
+6
What Column is Sulfur in on the periodic table?
Column 6 … Hmmmm
2.5
Do You Understand Oxidation State?
What is the oxidation state of Phosphorous in Phosphate?
+5
What Column is Phosphorous in on the periodic table?
Column 5 … Hmmmm
2.5
Some Polyatomic Ions
ammonium
SO4
2-
sulfate
CO32-
carbonate
SO32-
sulfite
HCO3-
bicarbonate
NO3-
nitrate
-
nitrite
-
NH4
+
ClO3
-
Cr2O7
2-
CrO42-
chlorate
NO2
dichromate
SCN
thiocyanate
chromate
OH-
hydroxide
Calculate the O.S. for the “ates” and “ites.”
Is there a pattern?
2.7
Patterns
•
•
•
•
•
•
Perchlorate ClO4Chlorate
ClO3Chlorite
ClO2Hypochlorite ClOChloride
ClDo you seen any patterns?
Chemical Nomenclature
• Ionic Compounds
– Cation is a metal ion or ammonium ion (NH4+)
– Anion (nonmetal), add “ide” to element name, or a
complex ion (“ate”, “ite”, etc)
BaCl2
barium chloride
K2O
potassium oxide
Mg(OH)2
magnesium hydroxide
KNO3
potassium nitrate
2.7
• Transition metal ionic compounds
– indicate charge on metal with Roman numerals
FeCl2
2 Cl- -2 so Fe is +2
iron(II) chloride
FeCl3
3 Cl- -3 so Fe is +3
iron(III) chloride
Cr2S3
3 S-2 -6 so Cr is +3 (6/2) chromium(III) sulfide
2.7