Transcript Slide 1

CHAPTER 2
ATOMS, MOLECULES AND
IONS
John A. Schreifels
Chemistry 211
1
Contents
• The Atomic Theory of Matter
–
–
–
–
The Discovery of Atomic Structure
The Modern View of Atomic Structure
Atomic weights
The Periodic Table
• Chemical Substances: Formulae and Names
– Ions and Ionic Compounds
– Naming Inorganic Compounds
• Chemical Reactions
John A. Schreifels
Chemistry 211
2
ATOMIC THEORY OF MATTER
(DALTON'S THEORY)
• Law of definite proportions led to theory that all
matter made up of atoms.
• Atoms- basic building blocks and don't change
when react with other atoms.
• Element- describes matter composed of only
one type of atom.
• Compound- combination of atoms in specific
proportions.
• Chemical reaction- atoms exchange partners
producing other compounds.
John A. Schreifels
Chemistry 211
3
LAW OF MULTIPLE
PROPORTIONS
• Some elements can form more than one compound
when they react together (C & O: CO and CO2; N & O:
N2O, NO, NO2, etc.). Dalton’s law predicted that the
mass proportions should be proportional. Experiment
confirmed this leading to this law.
• Law of multiple proportions: when two elements form
more than one compound, the ratio of the masses in one
compound divided by the ratio of these masses in the
other compound gives a ratio of small whole numbers.
E.g. There are three binary compounds that form between
barium and nitrogen. There was 4.9021 g , 9.8050 g and
14.7060 g of Ba per 1.0000 g N in the three compounds.
Show that these compounds obey the law of multiple
proportions.
John A. Schreifels
Chemistry 211
4
The Discovery of Atomic
Structure
•
•
•
•
Thompson - Cathode rays.
Milliken - Oil drops.
Rutherford - backscattering -particles.
Radioactivity, the spontaneous emission
of radiation from an atom led to the
discovery of -, -, and -rays.
John A. Schreifels
Chemistry 211
5
The Modern View of Atomic
Structure
• Building Blocks
– protons have a + charge, mp = 1.67 x 10-27kg
– neutrons are neutral, mn = mp
– electrons have a  charge, me = mp/1835
• Neutral atom: # electrons = # protons
• Mass of atom is found by adding the mass of
protons and neutrons
• Protons identify the element (# protons called
the atomic number, Z).
• Isotopes have varying numbers of neutrons,
1
2
3
1H , 1 H , 1 H
John A. Schreifels
Chemistry 211
6
Atomic and Molecular Weights
Atomic mass scale:
12
• A relative mass scale with the mass of the 6 C
isotope is defined as
exactly 12 amu (daltons) and used to determine the relative mass of all
elements.
• 1 amu = 1.6605x1024 g
• Mass of other atoms reported relative to this.
Average Atomic Masses
• Reported mass of carbon and other elements on periodic table do not
correspond to the expected value since they are weighted averages from all
of the isotopes.
AM obs  f1  AM1  f 2  AM 2  f3  AM 3  ...
where f1 = the fractional abundance of isotope 1 and AM = the atomic mass.
E.g. Determine the atomic mass of boron if the masses of the two isotopes are
10.013 amu and 11.009 amu and the fractional abundances are 0.1978 and
0.8022, respectively.
E.g. 2 Using the periodic table, determine the fractional abundance of the 35Cl
and 37Cl isotopes if their masses are 34.969 and 36.966, respectively.
John A. Schreifels
Chemistry 211
7
Periodic Table
1A
•
•
•
•
•
•
•
•
•
8A
H
2A
3A
4A
5A
6A
7A
He
Li
Be
B
C
N
O
F
Ne
Na
Mg
Al
Si
P
S
Cl
Ar
K
Ca
Sc
Ti
V
Cr
Mn
Fe
Co
Ni
Cu
Zn
Ga
Ge
As
Se
Br
Kr
Rb
Sr
Y
Zr
Nb
Mo
Tc
Ru
Rh
Pd
Ag
Cd
In
Sn
Sb
Te
I
Xe
Cs
Ba
La
Hf
Ta
W
Re
Os
Ir
Pt
Au
Hg
Tl
Pb
Bi
Po
At
Rn
---------------------------Transition Metals--------------------
Elements in a column have similar reactivity.
Blue elements are semi-metals (metalloids).
Elements to left of blue area are metals.
Elements to right of blue area are non-metals.
1A = Alkali metals
2A = Alkaline earth metals
6A =Chalcogens
7A = Halogens
8 A = Noble gases
John A. Schreifels
Chemistry 211
8
BONDING
•
•
An electron from each atom strongly interacts to form a bond.
Bonding can be either:
– Ionic: Occurs between metal atoms or between metal and nonmetal
atoms.
– Covalent: occurs between nonmetal atoms and forms molecules.
•
•
Covalent: sharing of electrons occurs.
Ionic: electron(s) is (are) transferred from one atom to the other to
produce
–
–
–
–
a positively charged substance (cation) and
a negatively charged substance (anion).
Ions bound by electrostatic attractions.
The formula of the ionic compound can be determined from the charge
on the cation and the anion (even with a polyatomic ion):
•
•
•
Mg2+ and Cl form an ionic compound with the formula: MgCl2.
Fe3+ and O2 form an ionic compound with the formula: Fe2O3.

Fe2+ and NO 3 form a compound with the formula: Fe(NO3)2
John A. Schreifels
Chemistry 211
9
NAMING INORGANIC
COMPOUNDS
IUPAC and Common Usage Methods of naming used for both organic and
inorganic compounds.
Organic compounds = predominantly carbon containing compounds.
Inorganic compounds = all others
Binary ionic compounds: compounds having a cation (a metal) and an anion
(one of the main group anions).
Cations:
• Accepted method: Roman numeral in parentheses to indicate the charge.
Not necessary when only one ionic charge possible. See Table 2.2.
• Common method: Remove ending and add either -ous or -ic to
• Latin form of the element used instead on some: Stannous, Stannic;
Ferrous, Ferric; Cuprous, Cupric.
Anions:
•
For monoatomic anions add -ide to the stem. Fluor-, Ox-, Nitr-, Sulf-, etc.
John A. Schreifels
Chemistry 211
10
NOMENCLATURE 2
Binary molecular compounds:
• More cationlike appears first; -ide ending is placed on
the anionlike substance.
– The more cationlike element appears to the left of or below the
other element in the periodic table
• With hydrogen as one of the two, hydrogen is first; place
an -ide on the other element.
• If a compound contains a group VI or VII element, an –
ide ending is added to it. Numerical prefixes are used
especially with the element listed second. Mono- not
used with the first element.
– When oxygen with fluorine, oxygen first in name: E.g. Oxygen
difluoride = OF2.
John A. Schreifels
Chemistry 211
11
Compounds with Polyatomic
ions
• Name these the same way that ionic binary compounds are named
replacing the name of the anion (in a few cases cation) with the
name of the polyatomic ion.
– Oxy anions (anions containing at least 1 oxygen atom): difficult
because there are often several possible anions.
– Add -ate to the stem (carbonate, sulfate, nitrate, etc); but
– Many oxyanions can have other proportions of oxygen e.g.SO32,  , SO 24 
These can be named by adding:
• per- x -ate for most oxygen
• -ite for a small number of oxygen
• hypo- x -ite gives least
• E.g. oxychlorides.
• If ion contains H, write: “hydrogen” + name of ion without hydrogen,
e.g. hydrogen sulfate.
• A prefix of mono- or di- to indicate the number of hydrogens may be
needed. E.g. dihydrogen phosphate- H
. 2 PO 4
John A. Schreifels
Chemistry 211
12
Oxyacids
• Binary compounds which are acids: Prefix
hydro- added to the anion part; change the
-ide ending to -ic.
H 2O
 HCl(aq) Hydrogen chloride
• HCl(g) 
becomes hydrochloric acid.
• The ending -ite is changed to -ous and ate to -ic.
John A. Schreifels
Chemistry 211
13
CHEMICAL EQUATIONS
•
•
Chemical reaction indicates the reactants and products.
Reactants on left; Products on right
–
–
–
•
•
2H2(g) + O2(g)  2H2O(l);
4Fe(s) + 3O2(g)  2Fe2O3(s)
NaCl(aq) + AgNO3(aq) AgCl(s) + NaNO3(aq)
Total number of each atom should be the same on each side of the
reaction. Law of Conservation of mass should guide us.
Steps to Balancing an Equation (simple):
–
–
–
Write an unbalanced equation with all reactants and products:
Balance by changing co-efficients
Reduce coefficients
E.g. the combustion of methanol produces water and carbon dioxide:
CH3OH(l) + O2(g)  CO2(g) + H2O(l)
E.g. Balance:
• P4 + N2O(g)  P4O6(s) + N2(g)
• P2O5 + H2O  H3PO4
John A. Schreifels
Chemistry 211
14