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Transcript
The Atom: From Philosophical Idea to
Scientific Theory

Democritus first suggested the idea that atoms
existed but had no experimental support
◦ Atom: the smallest particle of an element that keeps the
properties of that element.
 (Greek: atomos = indivisible)
Dalton’s Atomic Theory
1.
All elements are composed of tiny
indivisible particles called atoms.
Dalton’s Atomic Theory
2.
Atoms of the same element are
identical in size, mass and other
properties. Atoms of one element are
different from those of another.
Dalton’s Atomic Theory
3.
Atoms can combine with other atoms
in whole number ratios to form
compounds
H2 O
C12H22O11
NOT
H2.5O¾
Dalton’s Atomic Theory
4.
Chemical reactions occur when
atoms are separated, joined or
rearranged. Atoms are not changed
into atoms of another!
Dalton’s Atomic Theory
5.
Atoms can not be subdivided,
created or destroyed.

Atoms are known to be made up of
smaller subatomic particles
◦ Electrons
◦ Protons
◦ Neutrons


Dalton
A simple sphere with no internal structure
Thomson
 Discovered electrons
 Plum pudding model

(negatively charged particles)



Rutherford
Dense positive nucleus surrounded by electrons
Protons – positively charged particles
BBC Video
Gold Foil Expt



Bohr
Electrons orbit nucleus in certain energy levels
Planetary model


Shrodinger
Electrons exist in clouds around the nucleus





Protons (p+) = + charge; nucleus of the atom
Neutrons (n) = no charge; nucleus of the atom
Electrons (e-) = - charge; orbit the nucleus
Protons and neutrons determine mass
Electrons occupy most of the volume of the atom
and determine charge
WORLD OF
CHEMISTRY
Crash
Course
Atoms of different elements have different
numbers of subatomic particles
Number of protons in the nucleus
 Elements are arranged by atomic number
on periodic table
 Identifies an element
 Also tells you how many electrons in a
neutral atom


Periodic Table
◦ How many p+?
◦ How many e-?

Total # of protons and neutrons in an atom

Mass numbers are ALWAYS whole numbers
◦ When using the periodic table, round the atomic mass
Mass Number???

# of protons = atomic number

# of electrons = # of protons

# neutrons = Mass # - Atomic #
(in a neutral atom)
Symbol
p+
n0
e-
Atomic #
Mass #


ION = charged atom due to the gain or loss of
electron(s)
If an atom GAINS an electron = negative ion
◦ anion
◦ Ex: Cl-

If an atom LOSES an electron = positive ion
◦ cation
◦ Ex: Ca2+
Symbol
Atomic #
Mass #
#
protons
#
#
neutrons electrons
Charge

Definition – atoms of the same element with
different numbers of neutrons
◦ Isotopes differ in mass number
◦ Identified by mass number (ex: C-12 vs C-14)

Definition = weighted average mass
of the isotopes of the element

Reported on the periodic table

Based on the mass and abundance of each isotope
Atomic mass =
Abundance x mass
ISOTOPE #1
+
Abundance x mass
ISOTOPE #2
Repeats for however many isotopes exist for that
element….
Atomic mass =
Abundance x mass
+
Abundance x mass
Carbon has 3 isotopes:
carbon-14 abundance of 0.001%
carbon-13 abundance of 1.11%
carbon-12 abundance of 98.89
What is the atomic mass of carbon?
Atomic mass =
Abundance x mass
+
Abundance x mass
Chlorine has 2 isotopes:
chlorine-37 abundance of 75.78%
chlorine-35 abundance of 24.22%
What is the atomic mass of chlorine?
Chapter 5

Dmitri Mendeleev (1834-1907) – first person to
organize the elements in a chart
◦ Arranged ~ 70 elements by increasing atomic mass
◦ Left blank spaces for elements which were not
discovered yet

Henry Moseley (1913) – rearranged Mendeleev’s
periodic table
◦ Arranged elements by increasing atomic number
◦ Also grouped elements by their properties
◦ Current configuration of the Periodic Table

Elements are arranged by atomic number
◦ Columns = groups/families
◦ Rows = periods

Periodic Law: periodic repetition of
physical and chemical properties

Alkali Metals (group 1)
◦ React Violently with water
 Lithium
 Sodium
 Potassium
 Rubidium
 Cesium
 Francium

Alkaline Earth Metals (group 2)
◦ Very common in the earth’s surface






Beryllium
Magnesium
Calcium
Strontium
Barium
Radium

Transition Metals (Groups 3-12)
◦ Most of the common metals

Inner Transition Metals
◦ Placed at bottom of periodic table to condense table
◦ Lanthanide & Actinide Series
◦ All actinides are radioactive (unstable)

Halogens (group 17)
◦ Highly reactive




Fluorine
Chlorine
Bromine
Iodine

Noble Gases (group 18)
◦ All gases
◦ Do not react or combine with any other element

Line of Demarcation: jagged “stairs” which separate
the left and right side
◦ Metals = left and below the line of demarcation
◦ Nonmetals = right and above the line of demarcation
◦ Metalloids = B, Si, Ge, As, Sb, Te

Properties of Metals
◦ Conduct electricity & heat
◦ Malleable
◦ Strong
◦ High melting and freezing points
◦ Mostly solids
◦ Have Luster

Properties of Nonmetals
◦ Insulators – do not conduct well
◦ Brittle
◦ Low melting and freezing points
◦ Contain gases and liquids
◦ Are dull
Properties of Metalloids
 have properties of both metals and
nonmetals


Ex) Silicon
◦ -semi-conductor
◦ -brittle



Answer the following in your composition
book
Questions found on page 129
#33, 36, 38-43, 45-46, 48-49, 53, 57