Compounds & Molecules
Compounds & Molecules
• COMPOUNDS are a combination of 2 or
more elements in definite ratios by mass.
• The character of each element is lost when
forming a compound.
NaCl, salt
• MOLECULES are the smallest unit of a
Ethanol, C2H6O
compound that retains the characteristics of
the compound.
Buckyball, C60
MOLECULAR FORMULAS
WRITING FORMULAS
• Formula for glycine is C2H5NO2
• Can also write glycine formula as
• In one molecule there are
– 2 C atoms
– 5 H atoms
– 1 N atom
– 2 O atoms
–H2NCH2COOH
to show atom ordering
g
• or in the form of a structural
formula
H H O
H N C C O H
H
ELEMENTS THAT EXIST AS
DIATOMIC MOLECULES
MOLECULAR MODELING
H H O
H N C C O H
H
Ball & stick
Drawing of glycine
Space--filling
Space
Page 1
Ion Formation
Polyatomic Ions are groups of atoms with a
charge.
MEMORIZE the names and formulas in Table 2.5,
page 67.
• Atoms lose or gain electrons to become more stable
• This causes unbalanced charge in the atom, which is now
called an ion
• If an atom loses electrons it is a CATION (positive)
• If an atom gains electrons it is an ANION (negative)
COMPLETE THE CHART
Symbol
#p+
#no
#e-
15
17
18
8
8
Net
charge
23 Na1+
11
-2
Periodic Table
Symbol
#p+
#no
#e-
Net
charge
23 Na1+
11
11
12
10
+1
32 P33
15
15
17
18
-3
3
16 O28
8
8
10
-2
• Dmitri Mendeleev developed
the modern periodic table.
Argued that element
properties are periodic
functions of their atomic
weights..
weights
• We now know that element
properties are periodic
functions of their ATOMIC
NUMBERS..
NUMBERS
Periods - Periodic Table
Regions of the Periodic Table
• A period is a horizontal row on the periodic
table
• As you go from left to right the elements
change from metals to metalloids to
nonmetals to noble gases
Groups/Families - Periodic Table
•A group or family is a vertical column on the
periodic table
•Elements in a family have similar
characteristics due to the fact that they have
the same number of outer (valence) electrons
Page 2
Group 1A: Alkali Metals
Group 3A: B, Al, Ga, In, Tl
Most active metals
Metals in this group form a 3+ ion
Form a 1+ ion
Cutting
g sodium metal
Boron is a metalloid
Soft metals – stored in oil to prevent
reaction with water in air
Group 2A: Alkaline Earth Metals
Form a 2+ ion
Less reactive with water
React with air to form coatings on metals
Aluminum
Boron halides
BF3 & BI3
Group 5A: N, P, As, Sb, Bi
Group 4A: C, Si, Ge, Sn, Pb
Nonmetals in this group form a 3ion
Silicon and Germanium are
metalloids
Arsenic and antimony are
metalloids
Tin and lead are treated as
transition metals
White and red phosphorus
Group 6A: O, S, Se, Te, Po
C
Carbon
and silicon
ii
generally
do not form ions
The nonmetals in this
group form a 2- ion
Diamond
Tellurium and polonium
are metalloids
Quartz, SiO2
Sulfuric acid dripping from snotsnot-tite
in cave in Mexico
Group 7A:
F, Cl, Br, I, At
All are
diatomic
Transition Elements
These are the halogens
Often exhibit various
charges
They are all nonmetals and
form a 1- ion
Need a roman numeral in
name
They are the most reactive
nonmetals
Roman numeral tells
positive charge
Group 8A:He, Ne, Ar, Kr, Xe, Rn
•
•
•
•
•
•
Sulfur from a
volcano
Lighter than air balloons
“Neon” signs
Do not form ions
Only xenon has been forced to react
Very stable
NOBLE GASES
Lanthanides and actinides
Iron in air gives iron(III) oxide
Page 3