Transcript Elements - Heartland

Chapter 3
Elements
Periodic Table
Compounds
Elements
All words in the English language are the
result of the 26 letters of the alphabet.
All substances on our planet and the universe
are the result of about 88 known “building
blocks” called the elements.
Why 88?
Elements
An element cannot be decomposed into
a simpler substance.
The smallest particle of an element is
the atom.
Atoms are incredibly small.
Elements
Every element has a one or two letter
designation called its _____________.
In writing a symbol, the first letter is
capitalized and the second letter is
lowercase.
C = carbon
Co = cobalt
But, CO = a compound of carbon and
oxygen!
Distribution of the Elements
Most elements are solids at 25oC.
Br and Hg are liquids
 H, N, O, F, Cl, He, Ne, Ar, Kr, Xe, and Ra
are gases

Silicon and oxygen make up almost
75% of the Earth’s crust.
Distribution
Potassium
Sodium
2.4%
2.6%
Others
4.5%
Abundance
in Earth's
Crust
Calcium
3.4%
Iron
4.7%
Aluminum
7.5%
Silicon
25.7%
Oxygen
49.2%
History of the Elements
Some elements were known to ancient
man like Copper and Gold.
Names and symbols are based in Latin
language
Copper = Cuprum; symbol Cu
Gold = Aurum; symbol Au
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Common Elements
Aluminum
Argon
Arsenic
Barium
Boron
Bromine
Calcium
Carbon
Chlorine
Chromium
Cobalt
Copper
Fluorine
Helium
Hydrogen
Iodine
Iron
Lead
Lithium
Magnesium
Manganese
Mercury
Neon
Nickel
Nitrogen
Oxygen
Phosphorus
Potassium
Silicon
Silver
Sodium
Strontium
Sulfur
Tin
Titanium
Vanadium
Zinc
Periodic Table
Dimitri Mendeleev, 1869
Elements are arranged into vertical
columns called groups.

Elements within the same group tend to
react in the same way.
Horizontal row = period.
Periodic Table
Main (representative) groups = A
Transition groups = B
Groups with special names

Alkali metal, alkaline earth metal,
halogens, and the noble gases.
Actinide and lathanides.
Periodic Table
A stair-step line on the right-hand side
of the chart separates the metals from
the non-metals.
Metals are solids, have luster (shine),
are good conductors, are malleable,and
are ductile. Most have a high density
and high melting point.
Periodic Table
Non-metals are dull, are poor
conductors, and have low melting points
and densities.
Metalloids are elements that fall on or
near the line and have properties of
both metals and non-metals.

B, Si, Ge, As, Sb, Te, and Po
Hydrogen – a special exception.
Groups
Learning Check
Describe each in terms of a Group, Period,
and Metal, non-metal, or metalloid.
Element
Mg
C
Fe
As
Group
Period
M/NM
Elements in Nature
Elements are rarely found in their pure
form in nature.

Exceptions are metals like Gold, Silver,
and Platinum; non-metals like Nitrogen and
Oxygen; and the noble gases.
Most are combined with other elements
as compounds.
Diatomics
Some important elements occur as two
atoms bonded together.
The list is:
Compounds
Compounds are classified as either
Molecular or Ionic.
Molecular (aka covalent) compounds are
formed between two or more non-metals
who share electrons.
 Ionic compounds are formed between a
cation (+) and an anion (-).

Compounds
Metals lose electrons and form cations.

Na  Na+1 + 1e-
Non-metals gain electrons and form
anions.

Cl + 1e-  Cl-1
Thus, an ionic compound will have a
metal and a non-metal in its formula.
Compounds
Law of Constant Composition – any
sample of a compound will always have
the same ratio or mass percentage of its
elements.
Water always has two hydrogen atoms
and one oxygen atom per formula.
Sodium chloride always has one sodium
and one chlorine atom per formula.
Chemical Formulas
Are a shorthand method for writing
names.
Subscripts indicate the number of each
of the elements in the compound.
A subscript of one is NEVER written.
Ex) CO2, MgBr2, C6H12O6.
Learning Check
Decide whether the following would be a
molecular or ionic compound.
Compound
MgBr2
SO2
FeCl3
PF3
Type
Chapter 5
Atomic Theory
Discovery of Atomic Structure
Subatomic Particles
Nuclear Atom
Dalton’s Model
1.
2.
3.
4.
All matter is made up of tiny particles called atoms.
All atoms of a given element are similar to one
another; atoms of different elements are different
from each other.
Atoms of two or more different elements combine
to form compounds.
A chemical reaction involves the rearrangement of
atoms into new combinations. Atoms are never
created nor destroyed in a chemical reaction.
Parts of an Atom
Experiments performed around the turn
of the previous century (~1900),
showed that atoms were made of
several types of particles – collectively
referred to as subatomic particles.
These experiments showed that three
types of particles were present in an
atom.
Subatomic Particles
A proton has a +1 charge and an
approximate mass of 1 amu.
Note: an atomic mass unit (amu) is equal to
1/12 of the mass of a Carbon atom with 6
protons and 6 neutrons.
A neutron has no charge, but does have a
mass of about 1 amu.
An electron has a –1 charge and a mass so
small that we usually say that it weighs 0
amu.
Atomic Structure
Ernest Rutherford performed an experiment called
the “Gold Foil” experiment in 1911.
He used an alpha particle (2P + 2N) source and fired
them at a piece of very thin gold foil.
He expected all of the particles to pass straight
through. However, some were deflected and some
were even reflected backwards.
In Rutherford’s words, it was as if he had shot a
cannonball at a piece of tissue paper and have it
bounce backwards.
Gold Foil Experiment
Results
Only 1 in 8000 alpha particles is scattered.
Scattering occurs when an alpha particle encounters
a gold nuclei.
A nucleus is very small and contains both the protons
and the neutrons. Thus, it contains almost all of the
mass of an atom.
This very dense center is surrounded by the electron
cloud, which is occupied by the fast moving
electrons.
Thus, an atom is MAINLY EMPTY SPACE.
Atomic Model
Atomic Number & Mass Number
All atoms of the same element have the same
number of protons.
This distinguishes one element from another.
The number of protons is also called the
atomic number.
This is always the integer found on the
periodic chart with each chemical symbol.
Atomic Number & Mass Number
Atoms are electrically neutral. Thus, each
element must have an equal number of
protons and electrons.
The mass number of an atom is equal to the
sum total of the protons and neutrons in the
nucleus.
Mass number and atomic weight (found on
the periodic chart) are NOT the same thing.
Study Check
Name
Symbol
Atomic #
Carbon
Mass #
#P
#N
12
N
8
26
30
#e
Isotopes
All atoms of one element have the same
number of protons.
But, they can have different numbers of
neutrons, and hence, a different mass
number.
These different versions of atoms from
one element are called isotopes.
Isotopes
Use the chemical symbol, atomic
number (Z), and mass number (A) as
seen below.
Can also list symbol followed by mass
number.
Atomic Mass
The masses found for each element on
the periodic chart are the weighted
average of all the known isotopes for
that element.
Example: Chlorine has only two known
isotopes – Cl-35 and Cl-37. Cl-35 is
found 75.5% of the time and Cl-37 is
found 24.5% of the time.
Isotope Mass X Percent = Contribution
(approximate)
to total mass
35 amu
X
0.755
= 26.4 amu
37 amu
Totals
X
0.245
1.000
= 9.1 amu
35.5 amu
With all elements, round A.W.’s to one
decimal place.
Study Check
What is the Atomic Weight of each
element rounded to 0.1amu?
Na
 Si
 Cl
 K
