chapter 2: atoms, molecules, and ions the atomic theory of matter john dalton (1766-1844): elements...
TRANSCRIPT
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
The Atomic Theory of Matter
John Dalton (1766-1844): • Elements are made of tiny particles called atoms
• atoms of different elementscan combine to form compounds
• atoms are not created nor destroyed in chemical processes
• all atoms of one element are identical
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
The Discovery of Atomic Structure
J.J. Thomson (1856-1940): • discovered the electron
• electron: negatively chargedparticles of very small mass
• atoms of all elements containelectrons
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
R. Millikan (1868-1953):
• measured electron charge (oil-drop experiment)
electron charge = 1.60×10−19 C
The Discovery of Atomic Structure
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Ernest Rutherford (1871-1937):
(a) the atom has a positive charge concentrated in the nucleus
(b) the electrons orbit around the positive nucleus
(c) that the atom is mostly emptyspace
The Discovery of Atomic Structure
Gold-foil experiment:
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
+
Rutherford's Model:
The Discovery of Atomic Structure
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
The nucleus is structured:
PROTONS: positively charged (+1)
NEUTRONS: no charge
The Modern View of Atomic Structure
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
The mass of an atom is concentrated in its nucleus:
•proton: 1 atomic mass unit (1amu) +1
•neutron: 1 amu 0
•electron: negligible mass -1 (5.486 x 10-4 amu) (1.6 x 10-19C)
MASS Charge
The Modern View of Atomic Structure
1 amu = 1.66054 x 10-24 g
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Elements differ in their number of protons:
Hydrogen:1 proton
H1
the atomic number counts the number of protons
1
the mass number counts protons and neutrons
Helium:2 protons
2 neutrons
He24
Lithium:3 protons
4 neutrons
Li37
Beryllium:4 protons
5 neutrons
Be49
The Modern View of Atomic Structure
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
The Modern View of Atomic Structure
How about the neutrons?
• an element is defined by the number of protons
• atoms of one element can exist in different 'versions' :
all atoms must still have the same number of protons
but they may have a different number of neutrons
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
The Modern View of Atomic Structure
H1
1H3
1H2
1
Hydrogen or Protium
Deuterium Tritium
Isotopes of an element:
same number of protons but different number of neutrons
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Periodic Table
Elements are sorted according to atomic number
C6
12.01
Atomic Number
Atomic weight
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Periodic Table
Elements with similar properties fall in vertical groups
A row in the periodic table is called a period
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Average Atomic Mass = Atomic Weight
Average Mass = fraction of heavy x mass of heavy + fraction of light x mass of light
= 3/4 x 70amu + 1/4 x 30amu
= 0.75 x 70amu + 0.25 x 30amu = 60amu
30amu
70amu
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Average Atomic Mass = Atomic Weight
7Li
For example: Lithium AW = 6.939 amu
6Li Exact mass: 6.015 amu
Exact mass: 7.016 amu
Do the two isotopes exist in equal amounts ?
No, because the simple average of the isotope masses is:
(6.015 + 7.016) / 2 =
0.5 x 6.015 + 0.5 x 7.016 = 6.516
which is not the correct atomic weight
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Average Atomic Mass = Atomic Weight
7Li
For example: Lithium AW = 6.939 amu
6Li Exact mass: 6.015 amu
Exact mass: 7.016 amu
Which isotope is more abundant?
It must be 7Li because the average massIs closer to the mass of the 7Li isotope
The average is weighted in favor of the more abundant isotope
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Average Atomic Mass = Atomic Weight
7Li
For example: Lithium AW = 6.939 amu
6Li Exact mass: 6.015 amu
Exact mass: 7.016 amu
What are the fractions of the individual isotopes ?
X 6.015 + Y 7.016 = 6.939 X + Y = 1
X 6.015 + (1-X) 7.016 = 6.939
6.015 X + 7.016 – 7.016 X = 6.939
- 1.001 X = - 0.077
X = -0.077/ -1.001 = 0.0769
7.69% 6Li
92.31 % 7Li
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
number of electrons = number of protons = atomic number
Hydrogen:1 proton
H11
Helium:2 protons
2 neutrons
He24
Lithium:3 protons
4 neutrons
Li37
Beryllium:4 protons
5 neutrons
Be49
1 electron 2 electrons 3 electrons 4 electrons
How can you tell how many electrons an element has?
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
number of electrons number of protons number of neutrons
80Br-
40Ca2+
32S 16 32 – 16 = 1616
35 + 1 = 36
20 - 2 = 18
35
20
80 – 35 = 45
40 – 20 = 20
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Periodic Table
Most elements are metals
Alkali Metals
Alkaline Earth Metals
Noble Gases
Halogens
I A II A
III A IV A VA VI A VIIA
VIII A
Transition metals
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Molecules and Molecular Compounds
Some elements exist as diatomic molecules at room temp.
H2 N
2 O
2 F
2 Cl
2Br
2 I
2
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Molecules and Molecular Compounds
The periodic table helps predict how elements combine
Empirical Formulas Molecular Formulas
Only gives relative number of atoms in compound
Subscripts are smallestwhole-number ratios
Show actual number and types of atoms in a molecule
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Hydrogen peroxide
Empirical Formulas Molecular Formulas
H2O
2HO
Butane
C4H
10C2H
5
Propane
C3H
8C3H
8
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Drawing Molecules: methane
Space-filling model
Ball-and-Stick model
Structural formula
Perspectivedrawing
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Ions and Ionic Compounds
Ions are formed when a neutral atom
- gains electrons or- loses electrons
Li Li+
e-
Cation
BrBr
-Anion
e-
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
How can you tell how many electrons an element will gain/lose?
NOBLE GASES
Atoms tend to gain/lose the number of electrons neededto achieve the electron configuration of the closest noble gas
X1
Nb
X1 would lose 2 e- to get to the Nb configuration: X12+
X2
X2 would gain 3 e- to get to the N
b configuration: X23-
X3
Na
Nc
Nd
Ne
Nf
X3 would gain 1 e- to get to the N
e configuration: X3-
X4 would lose 1 e- to get to the N
c configuration: X4+
X4
Metals tend to form Cations Nonmetals tend to form Anions
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Li Li+
e-
Cation
BrBr
-Anion
Cations and Anions can combine to from Ionic Compounds
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Cations and Anions can combine to from Ionic Compounds
Ionic Crystal – not a discrete molecule
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Empirical Formulas for Ionic Compounds:
(A) determine charge of ions formed
(B) add ions so that compound is neutral overall
Na, O =>
Na+
2+ 2-
0
Na2O
Al, O =>
O2-Al3+
O2-
6+ 6-
0
Al2O
3
Na+ Al3+O2- O2-
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Li+
Br-
LiBr
Mg2+
Cl-
MgCl2
Li, Br =>
1+ 1-
0
Mg, Cl =>
2+ 2-
0
Cl-
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Empirical Formulas for Ionic Compounds:
Mg2+ MgCl
2
Al O3+ 2-Al
2O
3
O 2-
Ca2+ Ca
2O
2
CaO
smallest possible ratio!
Cl-1
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Naming Ionic Compounds: cations come first
(Ia) Monoatomic Cations:
Metal cations keep the name of the element:
Na+ Sodium ion Li+ Lithium ion Zn2+ Zinc ion
If a metal can form different kinds of cations (transition metals),the charge is indicated by a Roman Numeral:
Fe2+ Iron(II) ionFe3+ Iron(III) ionCo2+ Cobalt(II) ion
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Naming Ionic Compounds
(Ib) Cations formed from Nonmetals:
end in -ium:
NH4+ Ammonium ion H
3O+ Hydronium ion
+ +
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Naming Ionic Compounds
(IIa) Monoatomic and Simple Polyatomic Anions
Are derived from the element name by replacing the ending with -ide
N3- Nitride ion
O2- Oxide ion CN-
OH- Hydroxide ion
Cyanide ion
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Naming Ionic Compounds
(IIb) Oxyanions (polyatomic anions containing oxygen)
The most common oxyanion of an element ends in -ate One more oxygen: per-.....-ate One fewer oxygen: -ite Two fewer oxygen: hypo-.....-ite
Chlorate ClO3-
Perchlorate ClO4-
Chlorite ClO2-
Hypochlorite ClO-
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Naming Ionic Compounds
(IIb) Oxyanions (polyatomic anions containing oxygen)
The most common oxyanion of an element ends in -ate One more oxygen: per-.....-ate One fewer oxygen: -ite Two fewer oxygen: hypo-.....-ite
Sulfate SO42-
Sulfite SO32-
Hyposulfite SO22-
[ Persulfate SO52-, S
2O
82-
]
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Naming Ionic Compounds
Common Oxyanions:
SulfateSO
42-
Phosphate PO
43-
ChlorateClO
3-
BromateBrO
3-
IodateIO
3-
Nitrate NO
3-
Carbonate CO
32-
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Naming Ionic Compounds
You must know these!
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Naming Ionic Compounds
You must know these!
HCO3¯ Hydrogen carbonate ion
or Bicarbonate ion
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Naming Ionic Compounds: chemical formula → name
Identify the ions
Cation Anion
Transition metal ?Element name
Element name and charge in
Roman numerals
Group 1A, 2A, 3A metal?
Nonmetal ion?
-ide
monoatomic orsimple polyatomic
anion? oxyanion?
per ... ate... ate... ite
hypo ... iteMemorizee.g. Ammonium
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Naming Ionic Compounds: chemical formula → name
MgSO4
Mg2+
SO4
2-
→ simple cation: magnesium
→ oxyanion: sulfateMagnesium sulfate
FeCl3
Fe3+
3 Cl-
→ transition metal cation: Iron(III)
→ monoatomic anion: chlorideIron(III) chloride
NaClONa+
ClO-
→ simple cation: Sodium
→ oxyanion: hypochloriteSodium hypochlorite
NH4OH
NH4
+
OH-
→ cation: Ammonium
→ anion: hydroxideAmmonium hydroxide
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Naming Ionic Compounds: name → chemical formula
Identify the ions
CationAnion
Transition metal ?
Group 1A, 2A, 3A metal?
Charge is given in Roman numerals
Polyatomiccation?
Determine charge fromPeriodic Table
(Slide #25)Memorize...
Ammonium: NH4+
Determine charge
Polyatomicanion?
Memorize...Hydroxide: OH-
Cyanide: CN-
Oxyanions!
Determine charge
Monoatomic,nonmetal?
Determine charge fromPeriodic Table
(Slide #25)
combine cations & anions so that overall compound is neutral!
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Naming Ionic Compounds: name → chemical formula
Iron(II) chlorideFe2+
Cl- FeCl2
Remember to balance charge!
Potassium cyanideK+
CN-KCN
Magnesium hydroxideMg2+
OH- Mg(OH)2
More than onepolyatomic anion
(or cation)=> in parantheses!
Sodium sulfiteNa+
SO3
2-Na
2SO
3
x 2
x 2
x 2
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
What ions does ClO2 dissociate into?
(A) Cl- and 2 O2-
(B) Cl- and O22-
(C) Cl+ and O2-
(D) doesn’t form ions
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Naming Molecular Compounds
ClO2
does not dissociate into ions!
Metal cations + Nonmetal anions => ionic compoundsNonmetal cations + Nonmetal anions => ionic compounds(e.g. NH
4+)
Nonmetal + Nonmetal => molecular compounds
Before you start naming, determine what kind of compound you have!
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Naming Binary Molecular Compounds
ClO2
Name of the element farther to the left in the P.T. comes first- except oxygen, which is usually named last
If both elements are from the same group, the heavier one is named first
The second element is given an -ide ending
Greek prefixes indicate number of atoms of each element involved
Chlorine dioxide
[mono-, di-, tri-, tetra-, penta-, hexa-, hepta-, octa-, nona- , deca-]
[mono-prefix is never used with 1st element]
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Naming Compounds
NiO 1) Ionic or molecular?
2 a) Ionic: what are the ions? b) molecular: how many atoms?
=> ionic
=> Ni2+ and O2-
=> Nickel(II) oxide
SO => molecular
=> Sulfur monoxide
KMnO4 => ionic
=> K+ and MnO4-
=> Potassium permanganate
BF3 => molecular
=> Boron trifluoride
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Naming Compounds
Ca(BrO3)2
BrO3-
Calcium bromate Ionic or molecular compound?
Empirical formula?
Ions:
SO3
Sulfur trioxide
Ionic or molecular compound?
Name?
Charge on oxygen?
You can only assign “real” charges to ions in ionic compounds
You cannot determine the empirical formula of a molecularcompound simply by consulting the periodic table
SO3SO SO2
Ca2+
N/A