Nguyên tử Phân tử Ion

Atoms, Molecules, and Ions
Only in the last fifteen years has it become possible to “see” individual atoms.
Carbon atoms in graphite:
Dalton’s Atomic Theory
The modern view of matter did not emerge until 1806 with John Dalton’s atomic theory:
Each element is composed of atoms.
Atoms of a given element are all the same. Atoms of different elements are different.
Atoms are not changed into different atoms in a chemical reaction.
Compounds are formed when atoms of two or more elements combine.
Law of Multiple Proportions
In compounds of elements A and B, the ratio of masses of A and B are small whole numbers.
Water:
Hydrogen peroxide:
Hydrogen peroxide must contain twice as much oxygen as water.
The Structure of Atoms
In the mid-1800s, negatively-charged particles called electrons were discovered using cathode-ray tubes.
The Mass of an Electron
The mass/charge ratio was measured by J.J. Thomson using a cathode ray tube.
The charge of an electron was measured in a famous experiment by Robert Millikan.
The mass of an electron was found to be about 2000 times less than the lightest atom (hydrogen).
Radioactivity
Other particles were discovered being emitted from uranium.
 rays: Helium nuclei
 rays: High speed electrons
 rays: High energy photons (electromagnetic radiation)
The Nuclear Model
Rutherford’s gold foil experiment proved that most of an atom’s mass is found in a very small volume called the nucleus.
Protons, Neutrons, and Electrons
Two more subatomic particles were discovered in the early 1900s - protons and neutrons:
Particle Charge Mass (amu)
proton +1 1.0073
neutron 0 1.0087
electron -1 0.00055
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Units: 1 charge = 1.60210-19 Coulombs
1 atomic mass unit = 1.66010-24 g
1 A = 10-10 m
Atomic Symbols
The atomic number of an element is the number of protons in an atom.
Isotopes have the same number of protons but different numbers of neutrons.
The mass number of an isotope is the sum of protons and neutrons.
Isotopic symbols for two isotopes of carbon:
Carbon-12
Carbon-14
The Periodic Table
A chart of the elements in order of increasing atomic number arranged so that elements with similar chemical properties are in columns, or groups.
Atomic Elements
All metals and many semimetals consist of atoms grouped together.
The only elements that consist of isolated atoms are the rare gases He, Ne, Ar, Kr, Xe, and Rn.
The chemical formula for an atomic element is just the atomic symbol.
Molecules
A molecule is an assembly of two or more tightly bound atoms. Elements or compounds made up of molecules are called molecular.
The molecular formula indicates the number and type of each atom in a molecule.
Molecular elements: H2, N2, O2, F2, Cl2, Br2, and I2.
Molecular Compounds
Molecular compounds are composed of two or more nonmetals.
Compound Molecular Formula
Water H2O
Ammonia NH3
Methane CH4
Methanol CH3OH
Carbon dioxide CO2
Dinitrogen oxide N2O
Empirical Formulas
The empirical formula gives only the relative numbers of each element in a compound.
Analysis of a compound usually yields the empirical formula.
Molecular Formula Empirical Formula
C2H2 CH
C3H6 CH2
C4H10 C2H5
SO2 SO2
Ions
Atoms often gain or lose electrons to form charged ions. A postive ion is a cation, a negative ion is an anion.
Na atom - 1 electron  Na+ cation
11 protons 11 protons
11 electrons 10 electrons
Cl atom + 1 electron  Cl anion
17 protons 17 protons
17 electrons 18 electrons
Isotopic Symbols for Ions
Protons Neutrons Electrons
1H+
1
0
0
2H
1
1
1
19F
9
10
10
63Cu+2
29
34
27
140Ce+4
58
82
54
127I
53
74
54
235U
92
143
92
Ionic Compounds
A compound that consists of ions is an ionic compound. Its chemical formula is an empirical formula.

Microscopic view of NaCl:
Ionic Compounds
Metal atoms tend to lose electrons, non-metals tend to gain electrons.
As a general rule, compounds with a metal and a nonmetal in the formula are ionic compounds.
In ionic formulas, the charges sum to zero:
Ca+2 and Cl form CaCl2
Mg+2 and O2 form MgO
Fe+3 and S2 form Fe2S3
Predicting Charges
Group Charge
1 (1A) +1
2 (2A) +2
13 (3A) +3
15 (5A) -3
16 (6A) -2
17 (7A) -1
18 (8A) Don’t form ions
Polyatomic Ions
A polyatomic ion is a group of tightly bound atoms with an overall charge.
Hydroxide: OH Nitrate: NO3 Cyanide: CN
Carbonate: CO32 Sulfate: SO42
Phosphate: PO43
Ammonium: NH4+
You must learn the ions in Table 2.5!
What is the Formula?
beryllium & chlorine
BeCl2
calcium & sulfate
CaSO4
potassium & oxygen
K2O
magnesium & nitrate
Mg(NO3)2
ammonium & sulfur
(NH4)2S
barium & phosphate
Ba3(PO4)2
Chemical Nomenclature
There are different systems for naming compounds.
Organic compounds contain carbon. These compounds have a unique system of nomenclature.
We will examine the way inorganic compounds are named.
Inorganic Nomenclature
Inorganic compounds may have traditional names such as
H2O - water
NH3 - ammonia
CaSO4 - gypsum
...Or names related to their chemical formulas such as:
NaCl - sodium chloride
CO2 - carbon dioxide
Na2CO3 - sodium carbonate
Ionic Compounds
Cations
Cations formed from metal ions have the same name as the metal:
Mg+2 - magnesium ion
Zn+2 - zinc ion
If the metal has two or more oxidation states, the charge is indicated by a roman numeral
Cu+ - copper(I) ion
Cu+2 - copper(II) ion
Ionic Compounds
Polyatomic cations
There are only a few polyatomic cations - usually formed by adding H+ to a molecule:
NH3 - ammonia
NH4+ - ammonium ion
CH3NH2 - methylamine
CH3NH3+ - methylammonium ion
N2H4 - hydrazine
N2H5+ - hydrazonium ion
Ionic Compounds
Anions
Monatomic anions drop the element name and add -ide.
Cl- - chloride O-2 - oxide
Polyatomic anions containing oxygen use the name of the central atom with -ite or -ate.
Lower ox.# Higher ox.#
NO2- - nitrite NO3- - nitrate
SO3-2 - sulfite SO4-2 - sulfate
Ionic Compounds
Some anions add H+ to form a new anion. They contain the word “hydrogen”:
Na2CO3 - sodium carbonate
NaHCO3 - sodium hydrogen carbonate
Na3PO4 - sodium phosphate
NaH2PO4 - sodium dihydrogen phosphate
Acids
Acids are molecular compounds that contain hydrogen and an anion that is dissolved in water.
If the anion ends in -ide, the acid has the prefix hydro- and ends with -ic acid.
HCl - hydrochoric acid
HBr - hydrobromic acid
H2S - hydrosulfuric acid
Acids
If the anion ends in -ite, the acid ends in -ous acid.
HNO2 - nitrous acid
H2SO3 - sulfurous acid
If the anion ends in -ate, the acid ends in -ic acid.
HNO3 - nitric acid
H2SO4 - sulfuric acid
Binary Molecular Compounds
The element farthest to the left in the periodic table is named first.
If both elements are in the same group, the lower one is named first.
The suffix -ide is added to the second element.
Greek prefixes are used to indicate the number of each element (except for mono-).
P2O5 -
Diphosphorus pentoxide
Binary Molecular Compounds
Greek Number Prefix prefixes: 1 mono-
2 di-
3 tri-
4 tetra-
5 penta-
6 hexa-
7 hepta-
8 octa-
9 nona-
10 deca-
Name That Compound
SO3
sulfur trioxide
CuCl2
copper(II) chloride
PbCl2
lead chloride
BaH2
barium hydride
H3PO4
phosphoric acid
(NH4)2S
ammonium sulfide
N2O4
dinitrogen tetroxide