Download File

Chemistry
The Organization of Matter
The Organization of Matter
• Chemistry is the study of how all of the substances
that we know are structured and organized.
• Chemists are looking to try to better understand
how our world functions.
• What are the ingredients of matter?
• How do those ingredients form all of the matter
that we know?
• How do we classify the different types of matter
that exist?
The Atom
• All matter is composed of tiny particles that are
invisible to the naked eye. They are called atoms.
• Atoms are like the letters of the alphabet: they
allow us to arrange and re-arrange them in order
to create new substances.
• Atoms can be combined to create different
molecules. These molecules create all of the
matter that we know.
Atomic Theory
1. All matter is composed of tiny particles called
atoms.
2. Atoms themselves are formed of even smaller
particles: protons, neutrons and electrons.
3. Atoms are distinguished one from the other by
the number of protons, neutrons and electrons
that they have.
…
4. Atoms which have the same number of protons
are called elements.
▫
▫
Atoms of the same element are identical to each
other.
Atoms of different elements have different
properties and masses.
5. Atoms can be combined in chemical reactions to
form molecules.
The Atomic Model in History
• Many chemists in our history have contributed to
the understanding of atoms.
• Each of these chemists have propsed different
models to show this understanding of atoms and
to show how different atoms are related to one
another.
The Atom according to Democritus, 400
BCE.
• Democritus was the first to suggest that atoms
made up matter. The problem? The technology
didn’t exist to prove his theory.
• Atom = Greek for ‘cannot be divided’.
John Dalton, (1766-1844)
• Towards thw 1800’s, John Dalton, an English
scientist, proved the existence of atoms based on
his experiments with gases. He isolated and
classified six atoms: hydrogen, carbon, oxygen,
nitrogen, phosphorus and sulfur.
…
• Dalton’s model includes the use of balls of
different sizes and colours. These represent the
different atoms.
• A bar connects atoms together to show a chemical
bond, (a molecule).
The others…
• Many scientists have since improved atomic theory
in the 1800’s ad 1900’s, (Thomson, Rutherford,
Bohr, Chadwick).
• Today, we use the Bohr-Rutherford model,
represented like this:
Protons and neutrons in
the nucleus.
Electrons orbit the nucleus
on orbitals, (2 on the first,
8 on the second, 8 on the
third).
The Structure of the Atom
• Each atom contains protons, neutrons and electrons.
These are called subatomic particles.
• The protons have a positive charge, are found in the
nucleus of the atom and contribute to the mass of the
atom.
• The neutrons have no charge – they are neutral. They
are also found in the nucleus and contribute to the
mass of the atom.
• The electrons are found around the nucleus on
orbitals. They have a negative charge and no mass.
There are the same number of protons and electrons.
Molecules
• Atoms that are chemically linked together are
called molecules. The atoms in molecules can be
the same or different.
• Atoms link together after chemical reactions, when
the electrons of the two atoms react together.
• Molecules make up most of the matter that we
know. It is relatively rare for atoms to exist on
their own.
Chemical Formulas
Symbol for Hydrogen
Symbol for Oxygen
Indicates that there are 2 atoms
of hydrogen.
No number means
that there is only
one of that atom.
Rules for Writing Chemical Formulas
• Each capital letter indicates a new atom.
▫ If there is a lower-case letter, it is simply the seond
letter in the symbol of one atom.
• A small number, (subscript), indicates the quantity
of atoms. When there is no subscript, there is only
one of that atom.
• A large number before a chemical formula means
that there are multiples of that particular molecule.
▫ 2 H₂O
Mixtures
• Many types of matter are actually mixtures. A
mixture contains many elements and compunds
which are not chemically linked together, but just
exist together.
• Ex – Air, juice, tap water, etc.
Elements
• An element is all atoms with the same number of
protons.
• Ex – oxygen, hydrogen, gold.
• The number of protons is a characteristic property
of the elements.
• There are 118 different elements, 92 of which are
found naturally. The others were created in a lab.
The Periodic Table: The Building Blocks of
Matter
• The periodic table contains all of the elements,
natural and artificial that are currently known.
• These elements form all of the visible and invisible
matter that surround us.
• The periodic table is organized in a specific way to
show how the elements are related to one
another, and to tell us important informations
about them.
…
• The elements are classified according to their
horizontal and vertical axes.
• Horizontally:
▫ The elements are placed in increasing order of their
atomic number.
▫ The atomic number is the number of protons.
▫ Each horizontal line is called a period.
• Vertically:
▫ Each column represents a family.
▫ A family groups together elements with similar
properties.
▫ Ex – Group 18 is called the noble gases.
…
• Each box in the periodic table includes the same
information.
• Name of the Element:
▫ Hydrogen, oxygen, potassium, etc.
• Symbol of the Element:
▫ Either one capital letter or a capital letter and a lowercase letter. Ex – H, O, Ca
• Atomic Number:
▫ Indicates the number of protons that the element has.
• Atomic Mass:
▫ Indicates the number of protons + the number of
neutrons.
Summary
Atom
One type of matter. Na
Cl
O
Element
Multiple atoms of
the same type.
Molecule
Two atoms or more, O₂
same or different.
H₂
Compound
Two atoms or more, NaCl
but they are
H₂O
different. A
CO₂
molecule that
contains two
different atoms.
O₂
H₂
Na
Ar
NaCl
CO₂