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Transcript
What are elements?
On Earth, matter
usually can be
found as a
solid,
liquid,
or gas.
Elements and the Atomic
Structure
Elements



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 larger than 92 are
man-made and radioactive.
Elements are Made of Atoms


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
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.
–
The nucleus, which is made
up of protons and neutrons,
forms the center of an atom.


All atomic nuclei have a positive charge.
Elements are Made of Atoms
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



Surrounding the nucleus of an atom are
smaller particles called electrons.
–
An electron (e ) has little mass, but it has
a negative electrical charge.
An atom has an equal number of protons
and electrons which produces an atom
that has no overall charge.
Elements are Made of Atoms

An energy level represents the area in
an atom where an electron is most likely
to be found.
Electrons in Energy Levels





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


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.
Almost all atoms have isotopes
What Elements are Most
Abundant?
Compounds
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
–
–
Positive and negative ions attract each other.
An ionic bond is the attractive force between
two ions of opposite charge.
Ionic Bonding

Ions Travel




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

Compounds
Covalent Bonds
–
A covalent bond is the attraction of two
atoms for a shared pair of electrons that holds
the atoms together.
Compounds
–
A molecule is composed of two or more atoms
held together by covalent bonds.
Covalent Bonding
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

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

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

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

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
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



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



Mixing, stirring, or shaking
Heating
Crushing or grinding
Suspension
A mixture in which particles of
a material are dispersed throughout a liquid or gas but are large
enough that they settle out.
 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”

Colloids


A mixture in which the particles are
dispersed throughout but are not heavy
enough to settle out.
Made up of solids, liquids and gases.

Examples :
Mayonnaise
 Stick deodorant
 milk
