CHEMISTRY 161 Chapter 2. MATTER ATOMS MOLECULES ELEMENTS John Dalton matter is composed of...
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Transcript of CHEMISTRY 161 Chapter 2. MATTER ATOMS MOLECULES ELEMENTS John Dalton matter is composed of...
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CHEMISTRY 161
Chapter 2
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MATTER
ATOMS
MOLECULES
ELEMENTS
John Dalton
matter is composed of
‘building blocks’
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Dalton’s postulates
1. Elements are composed of small particles called atoms;atoms of an element are identical with same properties (mass)
2. Compounds are composed of atoms of more than one element; in a compound, the ratio of the number of atoms is an integer or fraction
LAW OF DEFINITE PROPORTIONS
3. A chemical reaction involves separation and combination of atoms; atoms are neither created nor destroyed
an atom is the basic, undividable unit of any element
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1. Law of definite proportions
2. Law of conservation of mass
in a chemical reaction
no gain or loss of mass is observed
unit of mass is g (gram) or kilogram (kg)
each atom has a constant mass
atomic mass – atomic weight
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Structure of an Atom
subatomic particles
electrons
protons neutrons
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proton,p 1.67262 × 10-27 kg +1.6022 × 10-19 C +1
electron,e 9.10939 × 10-31 kg -1.6022 × 10-19 C -1
m(p) / m(e) ≈ 1836
the atom’s positive charge is located in a small, dense central core ‘nucleus’
protons are a constituent of the nucleus
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+ ++ +
+
1. mass of the nucleus constitutes most of the mass of the atom
2. the nucleus is positively charged and contains protons
3. the nucleus constitutes only about 1/1013 space of an atom
4. electrons are as clouds around the nucleus
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proton, p 1.67262 × 10-27 kg +1.6022 × 10-19 C +1
electron, e 9.10939 × 10-31 kg -1.6022 × 10-19 C -1
neutron, n 1.67493 × 10-27 kg 0 0
Neutron
m(n) / m(e) ≈ 1838
m(n) > m(p)
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Structure of an Atom
subatomic particles
electrons(‘cloud’)
protons(nucleus)
neutrons(nucleus)
neutrons are the ‘glue’ of the nucleus
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Atomic Number and Mass Number(PSE)
AZXatomic number
(number of protons)
(number of electrons)
mass number
(number of protons plus neutrons)
in an atom, the number of electrons and protons are identical (charge neutrality)
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136C
6 electrons 6 protons
12 protons plus neutrons6 neutrons 126C
13 protons plus neutrons7 neutrons
6 electrons 6 protons
elements with same number of electrons and protons but different number of neutrons
ISOTOPES
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11H
31H
21H
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168O
11H
126C
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Periodic Table of the Elements
period
group
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Periodic Table of the Elements
8 main groupsmetals
nonmetalsmetalloids (semi metals)
metals – shine, conduct electricitynonmetals – do not shine, do not conduct electricitymetalloids – properties between metals and nonmetals
10 transition metal groups
lanthanides/actinides
metals
metals
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HOW HEAVY ARE ATOMS?
CALCULATION
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CHEMICAL MASS SCALE
standard / calibration
atomic mass unit (amu, u)
one atom of carbon-12 12 u (exactly)
we have to correlate u with kg
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MOLE
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one mole of a compound contains the same number of molecules/atoms as the number of atoms
in exactly 12 g of 12C
Avogadro’s numberNa
6.023 x 1023
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1 mole of H2O 6.023 x 1023
1 mole of 12C
6.023 x 1023
6.023 x 10231 mole of NaCl
1 mole of Na
6.023 x 1023
Avogadro’s numberlinks micro and
macroscopic world
molecules
molecules
atoms
atoms
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H2O
O: 15.999 u
H: 1.008 u
H: 1.008 u
H2O: 18.015 u
PSE
formula mass: weight of one moleculecorrelation between u and kg
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H2OO: 15.999 u
H: 1.008 u
H: 1.008 u
H2O: 18.015 u
1 mole of H2O – 18.015 g
15.999 g/mol
1.008 g/mol
1.008 g/mol
Na
Na
Na
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CaO
O: 15.999 u
Ca: 40.08 u
CaO: 56.08 u
1 mole of CaO – 56.08 g
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2 H2 + O2 2 H2O
2 molecules 1 molecule 2 molecules
2 moles 1 mole 2 moles
4.03176g 31.9988g 36.03g
STOICHIOMETRY
x g y g 70.0g
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2 H2 + O2 2 H2O
2 molecules 1 molecule 2 molecules
2 moles 1 mole 2 moles
4.03176g 31.9988g 36.03g
STOICHIOMETRY
x g y g 70.0g
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Example I: How many grams of iron are in a 15.0 g
sample of iron(III) oxide?
1. molecular formula
3. weight of one mole Fe2O3
2. weight of one molecule
Fe2O3
159.7 u
159.7 g4. 1 molecule Fe2O3 contains 2 atoms of Fe
5. 1 mole Fe2O3 contains 2 moles of Fe
159.7 g 111.69 g
15.0 g x gx = 10.5 g
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Example II:
How many atoms are in 10 kg of sodium?
1 mole sodium = 22.98977 g
6.023 x 1023 atoms = 22.98977 g
x atoms = 10,000 g
x = 2.6 x 1026 atoms
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Example III
How heavy are 1 million gold atoms?
1 mole gold = 196.96654 g
6.023 x 1023 atoms = 196.96654 g
1,000,000 atoms = x g
x = 3.2 x 10-16 g = 0.32 fg
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MOLEAvogadro’s number
Na
6.023 x 1023