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Key Terms
Nucleus Proton Neutron Electron Orbital Valence Electron -
Atomic Structure
What are atoms?
Atoms are tiny units that determine the
properties of all matter
4th Century BCE Democritus
Atom comes from the Greek word
meaning “unable to be divided”
He was unable to prove his ideas
In the 1700’s as chemistry developed, new
theories were developed
In 1808, John Dalton developed the
Atomic Theory
- all atoms of a given element were
exactly the same
- Atoms of different elements could join
to form compounds
Atoms are the building blocks of molecules
An atom is the smallest part of an element
that still has the elements properties.
What is an Atom?
atoms are made up of protons, neutrons,
and electrons
At the center of each atom is a small,
dense nucleus with a positive charge
The nucleus is made up of protons (+) and
neutrons (no charge)
protons and neutrons are almost
identical in size an mass but protons
have a positive charge and neutrons are
neutral
Outside the nucleus is a cloud of
negatively charged particles with very
little mass called electrons
The number of protons and electrons an
atom has is unique for each element.
Unreacted atoms have no charge.
Even though atoms are made up of
charged protons and electrons they are
not charged.
Atoms are not charged because they
have an equal number of protons and
electrons.
Models of the Atom
Bohr’s model compares electrons to
planets
In 1913 Niels Bohr suggested that
electrons of an atom move in a set path
around the nucleus.
Each electron has a certain energy that is
determined by its path around the
nucleus
* Gain energy to move to a higher energy
level (moving towards the nucleus)
* Lose energy to move to a lower energy
level (moving away form the nucleus)
Electrons act more like waves in their
movement
An electron’s exact location cannot be
determined. It is also impossible to
determine the speed and direction of an
electron.
Electrons exist in energy levels
The number of filled energy levels an atom
has depends on the number of electrons
1st energy level =
2nd energy level =
3rd energy level =
4th energy level =
2 e8e18e32e-
Electrons are found in an orbital within
energy levels
An orbital is the region in an atom where
there is a high probability of finding
electrons
There are four different kinds of orbital (s, p,
d, and f)
S-orbital is the simplest kind of orbital. Lowest
energy level
P-orbital has a dumbbell shaped orbital.
There are three different ways the orbits
can form higher than the S-orbit
D-orbital has five possible orbits
F-orbital has seven possible orbits highest
energy level
Every atom has between one and eight
valence electrons
A valence electron is an electron in the
outermost energy level of an atom. They
determine an atom’s chemical
properties and its ability to form bonds.
Key Terms
Periodic Law
Period
Group
Ion
Atomic Number
Mass Number
Isotope
Atomic Mass Unit (amu)
Average Atomic Mass
Organization of the Periodic Table
The periodic table groups similar
elements together. This organization
makes it easier to predict the properties
of an element based on where it is in the
periodic table.
The elements are represented by their
symbols and are placed in order based
on the number of protons an atom of
that element has in its nucleus.
Periodic Law states that when elements
are arranged by the number of protons,
similarities in their properties will occur in
a regular pattern.
The periodic table helps determine
electron arrangement
Horizontal rows (L - R) in the periodic
table are called periods
Elements in the same group (Up and
Down) have similar properties
Atoms of elements in the same group, or
column, have the same number of
valence electrons, so these elements
have similar properties
Some atoms form Ions
Atoms of group 1 elements are reactive
because their outer most energy level
contains only one electron.
Ionization is the process that an atom may go
through to gain or lose a valence electron.
This will allow the atom to have a full
outermost s and/or p orbital.
Ion is an atom or group of atoms that have
lost or gained one or more electrons and
have a negative or positive charge
Positive Ion is a cation
Negative Ion is an anion
Atomic number equals the number of
protons
The atomic number tells you how many
protons are in an atom. Since atoms are
always neutral it also tells you the
number of electrons.
The atomic number for a given element
never changes.
Mass number equals the total number of
subatomic (protons and neutrons)
particles in the nucleus.
The mass number of an atom equals the
number of protons plus the number of
neutrons.
The mass number only includes the number
of protons and neutrons because they
provide most of an atom’s mass.
Isotopes of an element have different
numbers of neutrons
Neutrons can be added to an atom
without affecting the number of protons
or electrons
Many elements only have one stable form
while others have different version of
their atoms (more neutrons)
These different versions are called isotopes
Isotopes very in mass but are still atoms of
the same element because they each
have the same number of protons and
electrons
Some isotopes are more common than others
Calculating the number of neutrons in an
atom
If you know the atomic number and the mass
number of an atom, you can calculate the
number of neutrons it has
Mass Number minus Atomic Number
The mass of an atom is very small
Atomic masses are usually expressed in
atomic mass units (amu)
Atomic mass is equal to one-twelfth of the
mass of a carbon-12 atom.
Average atomic mass for an element is a
weighted average, so the more commonly
found isotope has a greater effect on the
average than rare isotopes
Key Terms
Metal
Semiconductor
Alkaline-Earth Metal
Halogen
Nonmetal
Alkali Metal
Transition Metal
Nobel Gas
Families of Elements
How are elements classified?
By placing elements with similar physical
and chemical properties together
Elements are classified into three groups
Metal, Non-Metals, and Semiconductors
Metals
An elements that is shiny and conducts
heat and electricity well.
There are 4 types of Metals
1. Alkali
- very reactive
- located on the left edge of the
periodic table
- soft and shiny
- one valence electron
- not found in nature as elements
- stored in oil
2. Alkaline-Earth Metals
- compounds found in limestone and
human body
- located in group two (second column)
- two valence electrons
- less reactive than alkali metals
3. Transition Metals
- group 3-12
- not very reactive
- often found combined with other
elements as an ore
- conduct heat and electricity well
4. Synthetic Elements
- radioactive - continually decaying to
produce different elements
- all elements with an atomic number
greater than 92 are man made
Non-Metals
Except for hydrogen nonmetals are
located on the right side of the periodic
table.
They include some elements in groups 1316 and all elements in groups 17-18
Key Terms
Mole
Avogadro’s Constant
Molar Mass
Conversion Factor
Counting Things
There are many different counting units
The mole is useful for counting small particles
A mole (mol) is the base unit use to measure
the amount of substance whose number of
particles is the same as the number of atoms
of carbon in 12 g of carbon-12
Avogadro’s constant equals the number of
particles in one mol. 6.022 X 1023mol
Moles and grams are related
The mass in 1 mol of a substance is called its
molar mass.
Ex. 1 mol of carbon-12 atoms has a molar
mass of 12.00g.
The molar mass of an element in grams is the
same as its average atomic mass in amu,
which is listed in the periodic table.
Calculating with Moles
Conversion factors are ratios that are derived
from the equality of two different units and
that can be used to convert from one unit to
another
Using conversion factors
Relating amount to mass
An element’s molar mass can be used as a
conversion factor. Depending on which
conversion factor you use, you can solve for
either the amount of the element or its mass.