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Unit 6
Particles with
Internal Structure
The Elements

Remember, elements are combined to form molecules
the way letters are combined to form words.

Presently there are about 115 known elements.

Only 88 occur naturally, the rest are made in
laboratories.

Only 9 elements account for most of the compounds
found in the Earth’s crust.
Table 3.1
3-3
All living things
are made up,
mainly, of
oxygen, carbon,
hydrogen and
nitrogen.
3-4
Symbols For The Elements

Just as each state has a two-letter
abbreviation, each element has a oneor two-letter symbol to make life
simple for chemists.

Some elements found in the human
body are: As, Cr, Co, Cu, F, I, Mn, Mo,
Ni, Se, Si, & V.
 Notice
the first letter is
ALWAYS capitalized and the
second letter, if present, is
Not capitalized.
Symbols For The Elements

Some symbols make sense like O for
oxygen and H for hydrogen or Ni for
nickel.

Others, like Pb for lead or Fe for iron,
don’t automatically make sense; they
originated from the Greek or Latin
names of plumbum (Pb) and ferrum
(Fe).
Dalton’s Atomic Theory

Scientists studying matter in the eighteenth
century made the following observations:
 Most
natural materials are mixtures of
pure substances.
 Pure
substances are either elements or
combinations of elements called
compounds.
A
given compound always contains the
same proportions (by mass) of the
elements.
 John
Dalton attempted to explain these
observations in 1808.
Dalton’s Atomic Theory
1.
Elements are made of tiny particles called
atoms.
2.
All atoms of a given element are identical.
3.
The atoms of a given element are different
from those of any other element.
4.
Atoms of one element can combine with atoms
of other elements to form compounds. A given
compound always has the same relative
numbers and types of atoms.
5.
Atoms are indivisible in chemical processes.
That is, atoms are not created or destroyed in
chemical reactions. A chemical reaction
simply changes the way atoms are grouped
together.
Formulas of Compounds

The types of atoms and the number of each
type in each unit (molecule) of a given
compound are conveniently expressed by a
chemical formula.

The atoms are indicated by their symbols and
the number of each type is indicated by a
subscript (unless there is only one).
 Ex)
C6H12O6 or H3PO4
Practice

Write the formula for each of the following
compounds, listing the elements in the
order given:
a.
A molecule contains four phosphorous
atoms and ten oxygen atoms.
b.
A molecule contains one uranium atom
and six fluorine atoms.
c.
A molecule contains one aluminum atom
and three chlorine atoms.
What
is inside
an atom?
3-12
Modern Atomic Structure

Every atom is composed of the three basic
subatomic particles. (Protons, electrons,
neutrons)

Different elements have different numbers
of each of these subatomic particles.

The reason one element behaves differently
than another lies in the number and
arrangement of their electrons.

When atoms get close to each other their
electron “clouds” can overlap and interact.
Figure 3.9:
A nuclear atom
viewed in cross
section.
3-14

In any box on the Periodic Table, what information can you find?
6
C
12.01
Average Atomic Mass =
Protons + Neutrons
the weighted average of all
the mass numbers for each
isotope of the element
Atomic number = number of
protons, unique for every
element, no 2 elements have
the same atomic #
Element symbol = can be 1,2
or 3 letters, first letter is
always capitalized, and
succeeding letters are always
lower case
Isotopes

Two atoms of the same element (same number of
protons) with different numbers of neutrons.

Figure 3.10: Two isotopes of sodium.
Isotopes


There are two important numbers associated
with any given element:
1.
Atomic Number – The number of protons
in a nucleus.
2.
Mass Number – The SUM of the number of
protons AND neutrons (a.k.a. nucleons) in
a nucleus (NOT the sum of their masses).
We should note that two different isotopes
will have the same atomic number, but
different mass numbers.
Isotopes
 The
two previous examples of isotopes of
sodium would be:
23
11
Na
24
11
Na
•The example on the left would contain 11
protons and 12 neutrons (23-11=12).
•The example on the right would contain 11
protons and 13 neutrons (24-11=13).
Practice Problems

Write the symbol for each of the following atoms,
and list the number of protons, neutrons, and
electrons for each.
1)
The cesium atom with a mass number of 132.
2)
The iron atom with a mass number of 56.
3)
The krypton atom that has 48 neutrons.
4)
The nitrogen atom that has 6 neutrons.
Weighted Average Atomic Mass


Remember elements can have different isotopes which
means that they vary in their number of neutrons.
If you have 3 different isotopes of the same element:
 15 atoms have a mass of 21
 8 atoms have a mass of 23
 2 atoms have a mass of 19
We can calculate the weighted average by multiplying
the number of atoms by their mass:
(15) (21) = 315
537 = 21.48
(8) (23) = 184
25
(2) (19) =+ 38
average atomic mass
537
Using % to find Average Atomic Mass
Usually we only know the percents of
various isotopes that make up different
elements, we can use this to calculate the
average atomic mass.
 If we have 100% chlorine:
75.77% of mass is 35  .7577x35 = 26.52
24.23% of mass is 37.2423x37= 8.96
Add the 2 together to get the atomic mass:
26.52+ 8.96 = 35.48

Practice

Oxygen has 3 isotopes 16O, 17O, 18O
99.76% of mass is 16O
0.04% of mass is 17O
0.20% of mass is 18O
What is the average atomic mass?

Find the atomic mass if 99.64% of mass is
0.36% is 15N.
14N
and
A Simple Version of the Periodic Table
Periodic Table

When looking at periodic table elements are
arranged in horizontal rows by increasing atomic
number.

Horizontal rows are called “Periods”. Periods go
left to right
Periodic Table

The vertical columns are called “Groups” or
“Families”

Elements in families share similar properties
Metals, Semimetals, Non-Metals
All elements on the periodic table are grouped as
metals, semimetals or metalloids, or non-metals.
Due to the arrangement of the periodic table, it is
easy to identify each type of element.
Figure 3.12: Elements classified
as metals and nonmetals
Metals: Fall to left and under the stairs
Properties of Metals:
Efficient conduction of heat and electricity
Malleability
Ductility
A lustrous appearance
Positively charged ions
Non-Metals: Right and above the stairs
• Dull, Brittle
• Negatively charged ions
• Nonconductors
-insulators
Semimetals or Metalloids: Makeup the stairs
• Properties of both metals and nonmetals
• Semiconductors
Lanthanide and Actinide
Series

Mostly human made elements

Radioactive elements
Group 1A – Alkali Metals
Group 2A – Alkaline Earth Metals
Group 7A or 17: Halogen Family
Group 8A or 18: Noble Gases

Do not react easily with
anything, due stable electron
configuration

All other elements strive to
reach noble gas configuration
for maximum stability by
reacting with other elements.
Transition Metals: Group 3B-12B
Who is a solid, liquid or gas?
When we look at the elements on the
periodic table, who is a solid, liquid or
gas in their natural state?
 Most elements are not found in their
elemental state, most elements are
found in compounds with other
elements.
 Most elements on the periodic table are
solids, so we will point out those who are
gas or liquid.

Liquids
 Only
2 elements in their elemental
form are a liquid at 25 degrees
Celsius: Mercury and Bromine
Gases

More elements exist in
their elemental form as a
gas, but there are some
important distinctions to
make about these gases.

The noble gases are a gas,
called monatomic gases.
The prefix mono- means
one. And monatomic gases
exist as individual atoms.
Figure 3.13: A collection of argon
atoms.
Gases

There is another group of gases
called diatomic gases. The
prefix di- means two. These
elements travel in pairs as
molecules.
Figure 3.14: Nitrogen gas
contains NXN molecules.
Figure 3.14: Oxygen gas
contains OXO molecules.
Diatomic molecules
There are 7 elements that exist as diatomic molecules, you
will simply need to find a way to memorize these.
If you notice, all of the halogens fall in this category, and
then hydrogen, nitrogen, and oxygen.
What is an ion?

When we discussed atoms before, we were always
looking at a neutral atom.
Neutral atoms always have equal numbers of
protons and electrons.
protons = +1 charge
electrons = -1 charge

When atoms have unequal numbers of protons and
electrons, then the atom is a charged particle
called an ion.
Ion Facts

Ions are atoms, or groups of atoms,
with a charge.

The charge is created by different
numbers of protons and electrons.

In an atom ONLY electrons can move.

Atoms gain or lose electrons to become
ions.
Cations and Anions

There are 2 types of ions: cations and anions.

Cations are ions with a (+) positive charge. To form a
cation, an atom has lost electrons.
Example: Na loses an electron and becomes Na+

Anions are ions with a negative charge. To form an anion,
an atom has gained electrons.
Example: Cl gains an electron and becomes Cl-
Basic Names for Ions

Cations do not change names from their neutral
atoms.
Example: Magnesium loses 2 electrons and
becomes Mg2+ which is named magnesium ion.

Anions change the end of their name to –ide.
Example: Chlorine gains an electron and becomes
Cl-. We would change the name from chlorine to
chloride.
Some Common Anion Names
What would the names of the
following ions be?
 Chlorine =
 Fluorine =
 Bromine =
 Iodine =
 Oxygen =
 Sulfur =

How to Determine the Charge






When determining the charge for an atom we
can use the periodic table to help.
The number of valence electrons determines
the charge.
All atoms want 8 valence electrons.
If an atom has 1-3 valence electrons the atom
will lose them to become positive.
If an atom has 6-8 valence electrons the atom
will gain electrons to become negative.
We can determine the charge by looking at the
periodic table.
Figure 3.19: The ions formed by selected members
of groups 1, 2, 3, 6, and 7.
Practice

Determine the name and charge of the
following ions:
Potassium
Bromine
Calcium
Sulfur
Aluminum
Strontium
Cesium