Download Classification of Matter

Ch. 19: Properties
of Atoms and the
Periodic Table
Elements
 Remember
that elements are pure
substances that are made of only one
type of atom.
 Each element has its own name and
symbol.
 These names and symbols are displayed
on the periodic table.
 Elements are placed in the periodic table
based on what their atoms are like.
Atoms
 Atoms
are the smallest pieces of matter
that still act like an element.
 Atoms are made of three particles:
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Protons – have a positive charge and are
found in the center the atom (nucleus).
Neutrons – have NO charge and are found
in the center of the atom (nucleus).
Electrons – have a negative charge and
orbit OUTSIDE the center of the atom
Atoms
Atoms
An element gets its identity from the
number of protons that it has in its nucleus,
or center.
An element’s atomic number is equal to the
number of protons that it has.
If oxygen’s atomic number is 8, how many
protons does it have?
No two elements have the same atomic
number or the same number of protons.
Atoms
 To
be “happy” atoms need to have the
same number of electrons as they do
protons.
 For example, if an oxygen atom has 8
protons then it must also have 8 electrons.
 If the element carbon has an atomic
number of 6, how many protons and
electrons do its atoms have?
Electrons






When atoms bond, it is actually their electrons
that interact.
Electrons orbit the nucleus in levels. Each level
can hold a certain number of electrons.
1st level = 2
2nd -7th level = can hold up to 8
When one level is full, electrons begin to fill in
the next level.
All atoms want to have their outermost level
full of electrons.
Electrons
 The
electrons at the outermost edge of an
atom are what do all the bonding.
 These are called valence electrons.
Atoms
 Different
elements not only have different
atomic numbers but also different mass
numbers.
 Mass number is equal to the number of
protons added to the number of neutrons.
 Neutrons = mass number – atomic number