1. Atoms are the smallest particles that make up elements, consisting of a nucleus surrounded by electrons. John Dalton established the first atomic theory in 1808. 2. In the early 20th century, experiments by Thomson, Rutherford, and Chadwick led to discoveries about the internal structure of atoms, including the identification of protons, electrons, and neutrons within the nucleus. 3. Isotopes are atoms of the same element that differ in their number of neutrons. Molecules, ions, and compounds are formed through combinations and interactions between atoms.

1. Atoms, Molecules and Ions
Misch Puntod

2. 460
BC
Democritus develops the idea of
atoms
he pounded up materials
in his pestle and mortar
until he had reduced
them to smaller and
smaller particles which
he called ATOMA
(Greek for indivisible)

3. 1808
John Dalton
suggested that all
matter was made up of
tiny spheres that were
able to bounce around
with perfect elasticity
and called them
ATOMS

4. Dalton’s Atomic Theory (1808)
1. Elements are composed of extremely small particles
called atoms.
2. All atoms of a given element are identical, having the
same size, mass and chemical properties. The atoms of
one element are different from the atoms of all other
elements.
3. Compounds are composed of atoms of more than one
element. In any compound, the ratio of the numbers of
atoms of any two of the elements present is either an
integer or a simple fraction.
4. A chemical reaction involves only the separation,
combination, or rearrangement of atoms; it does not
result in their creation or destruction.

5. 2
Dalton’s Atomic Theory

6. 8 X2Y
16 X 8 Y
+

7. 1898
Joseph John Thomson
found that atoms
could sometimes
eject a far smaller
negative particle
which he called an
ELECTRON

8. J.J. Thomson measured the mass to charge ratio of the electron.
(1906 Nobel Prize in Physics)

9. Cathode Ray Tube

11. e– charge = –1.60 x 10–19 C
Thomson’s charge/mass of e– = –1.76 x 108 C/g
e– mass = 9.10 x 10–28 g
Measured mass of e-
(1923 Nobel Prize in Physics)
An X-ray beam
dislodges an electron
from air molecules
which becomes
attached to an oil
droplet.

13. (Uranium compound)

16. Check your Knowledge
What were the
observations of
ERNEST RUTHERFORD?

17. 1. atoms positive charge is concentrated in the nucleus
2. proton (p) has opposite (+) charge of electron (-)
3. mass of p is 1840 x mass of e- (1.67 x 10-24 g)
 particle velocity ~ 1.4 x 107 m/s
(~5% speed of light)
(1908 Nobel Prize in Chemistry)

18. atomic radius ~ 100 pm = 1 x 10–10 m
nuclear radius ~ 5 x 10–3 pm = 5 x 10–15 m
Rutherford’s Model of
the Atom
“If the atom is the Houston Astrodome, then
the nucleus is a marble on the 50-yard line.”

19. Chadwick’s Experiment (1932)
(1935 Noble Prize in Physics for discovery of neutron)
H atom has 1 p; He atom has 2 p
mass He/mass H should = 2
measured mass He/mass H = 4
 + 9Be 1n + 12C + energy
neutron (n) is neutral (charge = 0)
n mass ~ p mass = 1.67 x 10–24 g

20. mass p ~ mass n = 1840 x mass e–

21. Atomic number (Z) = number of protons in the nucleus.
Mass number (A) = number of protons + number of neutrons.
Isotopes are atoms of the same element (same number of
protons) but different numbers of neutrons in their nuclei.
X
A
Z
C
12
6 C
13
6 C
14
6
U
235
92 U
238
92
Mass Number
Atomic Number
Element Symbol
Atomic number, Mass number and Isotopes

22. The Isotopes of Hydrogen
Protium Deuterium Tritium
(radioactive)

23. 6 protons, 14 – 6 = 8 neutrons, 6 electrons
6 protons, 11 – 6 = 5 neutrons, 6 electrons
Do You Understand Isotopes?
How many protons, neutrons, and electrons are in C
14
6 ?
How many protons, neutrons, and electrons are in C
11
6 ?

24. Period
Group
Alkali
Metal
Noble
Gas
Halogen
Alkali
Earth
Metal

25. A molecule is an aggregate of two or more atoms in a
definite arrangement held together by covalent bonds.
H2 H2O NH3 CH4
A diatomic molecule contains only two atoms
H2, N2, O2, Br2, HCl, CO
A polyatomic molecule contains more than two atoms
O3, H2O, NH3, CH4

26. An ion is an atom, or group of atoms, that has a net
positive or negative charge.
Cation: ion with a positive charge
• If a neutral atom loses one or more electrons
it becomes a cation.
Anion: ion with a negative charge
• If a neutral atom gains one or more electrons
it becomes an anion.
Na
11 protons
11 electrons Na+ 11 protons
10 electrons
Cl
17 protons
17 electrons Cl-
17 protons
18 electrons

27. A monatomic ion contains only one atom.
A polyatomic ion contains more than one atom.
Na+, Cl–, Ca2+, O2–, Al3+, N3–
OH–, CN–, NH4
+, NO3
–

28. 13 protons, 13 – 3 = 10 electrons
34 protons, 34 + 2 = 36 electrons
Do You Understand Ions?
How many protons and electrons are in ?
Al
27
13
3+
How many protons and electrons are In ?
Se
78
34
2–

29. Common Monatomic Cations

30. Give the number of protons and
electrons in each of the following
common ions:
1) Na+ 5) Ca2+
2) Al3+ 6) I-
3) F- 7) S2-
4) O2- 8) N3-

32. A molecular formula shows the exact number of
atoms of each element in a molecule of the
substance.
An empirical formula shows the simplest
whole-number ratio of the atoms in a substance.
H2O
H2O
molecular empirical
C6H12O6 CH2O
O3 O
N2H4 NH2

33. Write the molecular
formula of A) methanol,
an organic solvent and
antifreeze; B) chloroform
(used as solvent and
cleaning agent) and C)
hydrogen peroxide from
its ball-and-stick model,
shown in the left.
C O
H
C
H
Cl
O
H

34. C
O
H
C
H
Cl
O
H

35. Write the empirical formulas for the
following molecules:
(a) acetylene (C2H2), which is used in welding
torches;
(b) glucose (C6H12O6), a substance known as
blood sugar;
(c) nitrous oxide (N2O), a gas that is used as
an anesthetic gas (“laughing gas”) and as
an aerosol propellant for whipped creams;
and
(d) caffeine (C8H10N4O2), a stimulant found in
tea and coffee.

36. An allotrope is one of two or
more distinct forms of an
element. Two allotropic forms of the
element carbon—diamond and
graphite—are dramatically different
not only in properties but also in their
relative cost.
Note that oxygen (O2) and ozone
(O3) are allotropes of oxygen.

37. ionic compounds consist of a combination of cations
and anions.
• the formula is always the same as the empirical formula
• the sum of the charges on the cation(s) and anion(s) in each
formula unit must equal zero
The ionic compound NaCl. Na+ to Cl– ratio = 1 to 1

38. Formula of Ionic Compounds
Al2O3
2 x +3 = +6 3 x –2 = –6
Al3+ O2–
CaBr2
1 x +2 = +2 2 x –1 = –2
Ca2+ Br–
Na2CO3
2 x +1 = +2 1 x –2 = –2
Na+ CO3
2–

39. Check Your Understanding
Match each of the diagrams shown
here in the following ionic
compounds: Al2O3, LiH, Na2S,
Mg(NO3)2. Green spheres represent
cations and red spheres represent
anions.

40. Monatomic negative ion names end in “ide.”

42. Write the formulas for the
following ionic compounds:
1) Sodium (Na+) oxide (O2-),
2) Iron sulfide (S2-)(containing
the Fe2+ ion),
3) Cobalt sulfate (containing
the Co3+ and SO4
2- ions), &
4) Barium fluoride (Ba2+, F-)

43. Chemical Nomenclature
Ionic Compounds
• often a metal + nonmetal
BaCl2 barium chloride
K2O potassium oxide
Mg(OH)2 magnesium hydroxide
KNO3 potassium nitrate

44. Transition metal ionic compounds
• Indicate the charge on the metal with Roman
numerals (the Stock naming system).
• Common names use the “ic” and “ous” endings.
FeCl2 2 Cl– = –2 so Fe is +2 iron(II) chloride
(ferrous chloride)
FeCl3 3 Cl– = –3 so Fe is +3 iron(III) chloride
(ferric chloride)
Cr2S3 3 S–2 = –6 so Cr is +3 chromium(III) sulfide

45. Cation Name Oxidation State
1) ________ Iron (III) 2) _________
Fe2+ 3) _______ 2+
4) ________ Cobalt (II) 2+
Ni2+ 5) ________ 2+

46. Anion Name Oxidation State
PO4
3- 6) _______ 3-
7) ________ sulfate 2-
OH- 8) ________ -

47. Name Formula
9) _______ N2O
Hydrogen sulfide 10) _____
Dichlorine heptoxide 11) ______

48. Molecular compounds
• Made of nonmetals or nonmetals +
metalloids.
• Use common names for these:
H2O, NH3, CH4
• The element further left in periodic
table is first.
• The element closest to bottom of
group is first.
• If more than one compound can be
formed from the same elements, use
the prefixes to indicate the number of
each kind of atom to specify the
compound.
• The last element ends in “ide.”

49. HI hydrogen iodide
NF3 nitrogen trifluoride
SO2 sulfur dioxide
N2Cl4 dinitrogen tetrachloride
NO2 nitrogen dioxide
N2O dinitrogen monoxide
Molecular Compounds
(Laughing Gas)

50. An acid can be defined as a substance that yields
hydrogen ions (H+) when dissolved in water.
• Pure substance, hydrogen chloride, HCl (g).
• Dissolve in water yields H+ and Cl– ions,
hydrochloric acid, HCl (aq).
An oxoacid is an acid that contains hydrogen,
oxygen, and another element.
HNO3 nitric acid
H2SO4 sulfuric acid
HNO3
HNO2 nitrous acid
H2SO3 sulfurous acid
H2CO3 carbonic acid

53. A base can be defined as a substance that yields
hydroxide ions (OH–) when dissolved in water.
NaOH sodium hydroxide
KOH potassium hydroxide
Ba(OH)2 barium hydroxide

54. Hydrates are compounds that have a specific
number of water molecules attached to them.
BaCl2•2H2O
LiCl•H2O
MgSO4•7H2O
Sr(NO3)2 •4H2O
barium chloride dihydrate
lithium chloride monohydrate
magnesium sulfate heptahydrate
strontium nitrate tetrahydrate
CuSO4•5H2O CuSO4