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Atomic theory
Matters are built from atoms.
John Dalton
(1768 -1828)
• Atoms are small, cannot be separated (by
chemical means).
• All atoms of the same element are the
same.
• Atoms cannot be destroyed, so the mass is
conserved.
• Atoms can combine differently to make
different compounds.
• Compounds of the same kind always have
the same number of each type of atom.
Do you see the atom?
Thompson’s cathode ray experiment
- How electron was found
electron:
charge
mass
= - 1.76 x 10 11 C/kg
Millikan Oil Drop Experiment
- How electron charge was measured
Charge for each electron:
1.602 x 10-19 Coulomb
Mass of electron:
9.10 x 10-28 g
Picture of an atom (~1900)
Thompson model
Where to find the α particles?
- Rutherford’s experiment
http://www.metacafe.com/fplayer/109587/bullets_path.swf
Where to find the a particles?
- Rutherford’s experiment
Where to find the a particles?
- Rutherford’s experiment
Anatomy of atom
nucleus
Anatomy of atom
Atomic theory
Matters are built from atoms.
•
•
•
•
•
Atoms are small, cannot be separated (by chemical means).
All atoms of the same element are the same.
Atoms cannot be destroyed, so the mass is conserved.
Atoms can combine differently to make different compounds.
Compounds of the same kind always have the same number of each
type of atom.
Atomic theory
H
2 protons → He
100
___ protons → Fm
Au
79 protons → ____
1 proton →
How to denote an atom?
mass number (protons + neutrons)
number of protons
(atomic number)
23
Na
11
symbol of
the element
How to denote this atom?
A
X
Z
(1) How many protons?
(2) What is the symbol for this
element?
(3) How many neutrons?
(4) What is its mass
number?
What atom is it?
A
X
5
(1) How many protons?
(2) What is the symbol for this
element?
(3) How many neutrons?
(4) What is its mass
number?
What atom is it?
A
B
5
(1) How many protons?
(2) What is the symbol for this
element?
(3) How many neutrons?
(4) What is its mass
number?
What atom is it?
10
B
5
(1) How many protons?
(2) What is the symbol for this
element?
(3) How many neutrons?
(4) What is its mass
number?
What atom is this one?
What atom is it?
10
B
(1) How many protons?
(2) What is the symbol for this
element?
(3) How many neutrons?
(4) What is its mass
number?
How to denote these atoms?
1
1H
2
1H
(D)
3
1H
(T)
Isotopes:
• Same number of protons
• Different number of neutrons
Different
mass!
Isotopes
Ions
Electrons are loosely
bond to the nucleus.
An atom can lose or gain
electrons.
A neutral atom: number of protons (+) = number of electrons (-)
An ion: a neutral atom loses or gain electrons
number of protons (+) ≠ number of electrons (-)
cation: more protons, thus positively charged
anion: more electrons, thus negatively charged
Ions
12
C
(6 p+, 6e- )
neutral atom
take1 extra electron:
-
12
C
(6 p+, 7e- )
anion
Ions
12
C
(6 p+, 6e- )
neutral atom
lose 1 electron:
-
12
+
C
(6 p+, 5e- )
cation
Ions
Ca
lose or gain
? electrons
Ca
2+
Fill in the blanks
Symbol
O2-
16
Number of protons
1
6
Number of neutrons
0
7
Number of electrons
0
3
Mass number
Atomic number
Fill in the blanks
Symbol
Number of protons
O2-
16
1
6
Number of neutrons
0
7
Number of electrons
0
3
Mass number
Atomic number
8
Fill in the blanks
Symbol
Number of protons
O2-
16
1
6
Number of neutrons =16-8=8
0
7
Number of electrons
0
3
Mass number
Atomic number
8
Fill in the blanks
Symbol
Number of protons
O2-
16
1
6
Number of neutrons =16-8=8
0
7
Number of electrons =8+2=10
0
3
Mass number
Atomic number
8
Fill in the blanks
Symbol
Number of protons
O2-
16
1
6
Number of neutrons =16-8=8
0
7
Number of electrons =8+2=10
0
3
Mass number
Atomic number
8
16
Fill in the blanks
Symbol
Number of protons
O2-
16
8
1
6
Number of neutrons =16-8=8
0
7
Number of electrons =8+2=10
0
3
Mass number
16
Atomic number
8
Atomic theory
H2O
CO2
Atomic theory
?
?
Molecular compounds
• No ions!
• Mostly compounds by non-metal
atoms.
• Examples:
Empirical formulas
Empirical formulas give the lowest
whole-number ratio of atoms of
each element in a compound.
Molecular formula
Empirical formula
H2O2
HO
C2H4
CH2
C3H6
?
H2O
?
Empirical formulas
Empirical formulas give the lowest
whole-number ratio of atoms of
each element in a compound.
Molecular formula
Empirical formula
H2O2
HO
C2H4
CH2
C3H6
CH2
H2O
H2O
Ionic compounds
molecular formula for
magnesium nitride?
Mg2+ N3-
What is the molecular formula for
sodium oxide
Chromic bicarbonate
Iron(III) phosphate
What does each number
mean?
H 2SO 4
2 SO 4
2−
3 Mg
14
2
2+
N H3