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What are elements?
On Earth, matter usually can be found as a
solid, liquid, or gas.
Elements and the Atomic
Structure
Elements
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All matter is made elements.
An element is a substance that cannot be
broken down into simpler substances by
physical or chemical means.
Ninety-two elements occur naturally on
Earth
and in the stars.
Elements are Made of Atoms
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Each element has distinct
characteristics.
An atom is the smallest particle of an
element that has all of the characteristics
of that element.
Elements are Made of Atoms
The nucleus, which is made up of
protons and neutrons, forms the center of
an atom.
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A proton (p+) is a tiny particle that has mass
and a positive electrical charge.
A neutron (n0) is a particle with about the
same mass as a proton, but it has no
electrical charge.
All atomic nuclei have a positive charge.
Elements are Made of Atoms
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The number of protons and neutrons in
different atoms varies widely.
The atomic number is the number of protons
in an atom’s nucleus.
The mass number or atomic mass is the
combined number of protons and neutrons,
which are in the nucleus.
Elements are Made of Atoms
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An electron (e ) has little mass, but it has
a negative electrical charge.
Surrounding the nucleus of an atom are
smaller particles called electrons.
An atom has an equal number of protons
and electrons which produces an atom that
has no overall charge.
Elements are Made of Atoms
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An energy level represents the area in
an atom where an electron is most likely
to be found.
Electrons in Energy Levels
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The number of electrons in the outermost
energy level determines the chemical behavior
of the different elements.
Valence electrons are the outermost electrons
in an atom.
Elements with the same number of valence
electrons have similar chemical properties.
Group 1 has 1 valence electron, group 2 has 2,
13 has 3, 14 / 4, 15 / 5, 16 / 6, 17 / 7, 18 / 8.
Isotopes
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The number of neutrons in the nuclei of
an element’s atoms can vary.
Isotopes are atoms of the same element
that have different mass numbers and the
same chemical properties.
What Elements are Most
Abundant?
Compounds
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A compound is a substance that is
composed of atoms of two or more different
elements that are chemically combined.
Most compounds have totally different
properties from the elements of which they
are composed.
Chemical bonds are the forces that hold the
elements together in a compound creating a
state of stability.
Ions
Ionic Bonds
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Positive and negative ions attract each other.
An ionic bond is the attractive force between
two ions of opposite charge.
Ionic Bonding
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Ions Travel
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Group 1 travels to group 17
Group 2 travels to group 16
 Metals and non metals attract
All compounds are looking to become stable
with 8 valence electrons.
Properties of ionic bonding
Brittleness
 High melting points
 Good electrical conductivity
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Compounds
Covalent Bonds
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A covalent bond is the attraction of two
atoms for a shared pair of electrons that holds
the atoms together.
Compounds
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A molecule is composed of two or more atoms
held together by covalent bonds.
Covalent Bonds
Covalent Bonding
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Formed when non-metal atoms share
valence electrons
7 + 7 =16
6 + 6 =16
 Use a dot diagram to predict how an atom will
share it’s valence electrons
Mixtures and Solutions
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A mixture is a combination of two or more
components that are NOT chemically
combined, and retain their identities.
Mixtures can be physically separated.
The identities of the substances DO NOT
change.
•A homogeneous mixture is also called a
solution.
Mixtures
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When a mixture’s components are easily
recognizable, such as pizza, it is called a
heterogeneous mixture.
• In a homogeneous mixture such as
chocolate milk, the component particles
cannot be distinguished, even though
they still retain their original properties.
Mixtures
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Common Techniques for Separating
Mixtures
Distillation – separates a mixture based on boiling
points of the component
Examples :
saltwater
crude oil into gasoline and kerosene
Magnet – separates iron from other objects.
Centrifuge – spins and separates according to densities.
Solutions
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A mixture that appears to be a single
substance but is composed of particles
of two or more substances that are
distributed evenly amongst each other.
•A solution may be liquid, gaseous, or solid.
Examples of solutions
Liquid - seawater
Gas - air
Solid - alloys
Solutions
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Dissolving – The process in which particles of
substances separate and spread evenly amongst
each other.
• Solute – substance that is dissolved. A solute is
soluble, or able to dissolve.
• A substance that is insoluble is unable to
dissolve, forms a mixture that is not
homogeneous, and therefore NOT a solution.
• Solvent – substance in which solute is dissolved.
Solubility
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The solubility of a solute is the amount of solute needed
to make a saturated solution using a given amount of
solvent at a certain temperature.
Solubility is usually expressed in grams of solute per 100
ml of solvent (g/100ml)
Three (3) methods that affect solubility
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Mixing, stirring, or shaking
Heating
Crushing or grinding
Suspension
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A mixture in which particles of a material
are dispersed throughout a liquid or gas
but are large enough that they settle out.
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Particles are insoluble, so they DO NOT
dissolve in the liquid or gas.
Particles can be separated using a filter.
Examples:
 Salad dressing
 Medicines that say “shake well before use”
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Colloids
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A mixture in which the particles are dispersed
throughout but are not heavy enough to settle
out.
Made up of solids, liquids and gases
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Examples :
Mayonnaise
Stick deodorant
milk