1. CHEMISTRY 161
Chapter 2

2. MATTER ATOMS MOLECULES ELEMENTS John Dalton matter is composed of
‘building blocks’
MOLECULES
ELEMENTS

3. an atom is the basic, undividable unit of any element
Dalton’s postulates
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

4. 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

5. Structure of an Atom
subatomic particles
electrons
protons
neutrons

6. protons are a constituent of the nucleus
proton,p × kg × C +1
electron,e × kg × 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

7. mass of the nucleus constitutes most of the mass of the atom + + + + +
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

8. Neutron m(n) / m(e) ≈ 1838 m(n) > m(p)
proton, p × kg × C +1
electron, e × kg × C -1
neutron, n × kg
m(n) / m(e) ≈ 1838
m(n) > m(p)

9. Structure of an Atom subatomic particles electrons (‘cloud’) neutrons
(nucleus)
protons
(nucleus)
neutrons are the ‘glue’ of the nucleus

10. Atomic Number and Mass Number
(PSE)
mass number
(number of protons plus neutrons)
atomic number
(number of protons)
(number of electrons)
in an atom, the number of electrons and protons are identical
(charge neutrality)

11. ISOTOPES 6 neutrons 12 protons plus neutrons 6 electrons 6 protons
elements with same number of electrons and protons but different number of neutrons
ISOTOPES

14. Periodic Table of the Elementsg r o u p

15. Periodic Table of the Elements
metals
nonmetals
metalloids (semi metals)
8 main groups
10 transition metal groups
metals
lanthanides/actinides
metals
metals – shine, conduct electricity
nonmetals – do not shine, do not conduct electricity
metalloids – properties between metals and nonmetals

16. HOW HEAVY ARE ATOMS?
CALCULATION

17. standard / calibration
CHEMICAL MASS SCALE
standard / calibration
atomic mass unit
(amu, u)
one atom of carbon u (exactly)
we have to correlate u with kg

18. MOLE

19. 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 number Na
6.023 x 1023

20. links micro and macroscopic world
6.023 x 1023
1 mole of H2O
molecules
6.023 x 1023
atoms
1 mole of 12C
6.023 x 1023
atoms
1 mole of Na
molecules
6.023 x 1023
1 mole of NaCl
Avogadro’s number
links micro and macroscopic world

21. formula mass: weight of one molecule
H2O
PSE
O: u
H: u
H2O: u
formula mass: weight of one molecule
correlation between u and kg

22. H2O O: 15.999 u H: 1.008 u H2O: 18.015 u 1 mole of H2O – 18.015 g Na
g/mol Na
1.008 g/mol Na
1.008 g/mol
1 mole of H2O – g

23. CaO
O: u
Ca: u
CaO: u
1 mole of CaO – g

24. 2 H2 + O2 2 H2O STOICHIOMETRY 2 molecules 1 molecule 2 molecules
2 moles mole moles
g g g
x g y g g
STOICHIOMETRY

25. 2 H2 + O2 2 H2O STOICHIOMETRY 2 molecules 1 molecule 2 molecules
2 moles mole moles
g g g
x g y g g
STOICHIOMETRY

26. How many grams of iron are in a 15.0 g sample of iron(III) oxide?
Example I:
How many grams of iron are in a 15.0 g
sample of iron(III) oxide?
1. molecular formula
Fe2O3
2. weight of one molecule
159.7 u
3. weight of one mole Fe2O3
159.7 g
4. 1 molecule Fe2O3 contains 2 atoms of Fe
5. 1 mole Fe2O3 contains 2 moles of Fe
159.7 g g
15.0 g
x g
x = 10.5 g

27. How many atoms are in 10 kg of sodium?
Example II:
How many atoms are in 10 kg of sodium?
1 mole sodium = g
6.023 x 1023 atoms = g
x atoms = 10,000 g
x = 2.6 x 1026 atoms

28. How heavy are 1 million gold atoms?
Example III
How heavy are 1 million gold atoms?
1 mole gold = g
6.023 x 1023 atoms = g
1,000,000 atoms = x g
x = 3.2 x g = 0.32 fg

29. MOLE
Avogadro’s number Na
6.023 x 1023