2. Atomic Theory
• What is an atom? In 430 BCE, Democritus proposed that all matter
consisted of small pieces that were indivisible
• He called them atomos (= “uncuttable”)
• Atom: The smallest particle that can still be considered an element
Lesson 1 Atomic Theory
3. History of Atomic Theory
John Dalton’s Theory (1600s):
1. All elements consist of atoms that cannot be divided.
2. All atoms of the same element are exactly alike and have the same
mass.
3. An atom of one element cannot be changed into an atom of
another element.
4. Compounds are formed when atoms of more than one element
combine in a specific ratio.
Lesson 1 Atomic Theory
4. History of Atomic Theory
• JJ Thomson (1897) discovered atoms contain negatively charged particles –
now called electrons
• Proposed that atoms contained electrons scattered in a ball of positive
charges
• “Plum Pudding Model”
Lesson 1 Atomic Theory
5. History of Atomic Theory
• Ernest Rutherford (1911)
discovered that atoms are
mostly empty space
• Also discovered the nucleus:
the dense positively charged
center
• Named the positive particles
in the nucleus of the atom
“protons”
Lesson 1 Atomic Theory
6. History of Atomic Theory
• Niels Bohr (1913)
revised Rutherford’s
model
• Suggested that
electrons move in
orbits around the
nucleus
• Each electron orbit
has a fixed energy
Lesson 1 Atomic Theory
7. History of AtomicTheory
• Cloud Model (1920s)
• Electrons found to move rapidly
through a cloudlike region –not
through specific orbits as Bohr
suggested
Lesson 1 Atomic Theory
8. History of Atomic Theory
• James Chadwick (1932) named
another particle in the atom: the
neutron.
• Neutron: Has no electric charge
Lesson 1 Atomic Theory
9. The Nature of Matter (In a Nutshell)
• Atom: Basic unit of matter…consist of
• Proton: Positively charged
• Neutron: No charge
• Electron: Negatively charged
Located in the nucleus
The number of protons in an
atom will always equal the
number of electrons in the
atom (for now at least, ions
are another story)
But why?
Having an equal amount of
positive charges and
negative charges ensures
that the atom will be
neutral
11. Recap
Periodic Table: (Thanks Mendeleev!) A chart showing all of the elements arranged
according to the repeating pattern of their properties.
Rows: Periods
Columns: Groups
Like Colors: Families
12. Using the Periodic Table
Element Name Atomic Number:
Represents number of
protons
…and electrons in a balanced atom
Element Symbol
Atomic Mass: Round
it to find the amount
of protons + neutrons
13. Periods in The Periodic Table
Some periods have special properties…
Lanthanides and Actinides, the lone rows under the table.
Found in nature
Rare earth metals
Not found in nature
(Except uranium and thorium)
Are all radioactive
Actinides that occur after uranium are called “transuranium elements”
--None of these elements are stable and they each radioactively decay
into other elements (WOAH!!!)
14. Groups in The Periodic Table
#1 Alkali Metals
• Very reactive
• Never found as free elements in nature (only in compounds)
• Shiny, soft
15. Groups in The Periodic Table
#2 Alkaline Earth Metals
• Hard, dense
• Very reactive –just not as much as the alkali metals
• Never free in nature
16. Groups in The Periodic Table
#3 Transition Metals
• Can be found in pure form in nature
• Metals –exactly as you’d expect them to be
• Good conductors of heat
17. Groups in The Periodic Table
#4 Alkaline Earth Metals
• Hard, dense
• Very reactive –just not as much as the alkali metals
• Never free in nature
18. Groups in The Periodic Table
#5 The Boron Family
• Contains Boron (shocker)
• Also other transition metals
19. Groups in The Periodic Table
#6 The Carbon Family
• Contains Carbon!
• And other metalloids
20. Groups in The Periodic Table
#7 The Nitrogen Family
• Contains two nonmetals
• Two metalloids
• Antimony
• And……. NITROGEN
21. Groups in The Periodic Table
#8 The Oxygen Family
• Oxygen and some nonmetals/metalloids
22. Groups in The Periodic Table
#9 The Halogen Family
• Nonmetals
• “Salt forming”
23. Groups in The Periodic Table
#9 The Noble Gases
• Do not typically form compounds
• Synthesized into compounds in labs
