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Elements
Ch. 2
CHAPTER
6
• Matter is made of atoms and every element has its own unique
type of atom.
• Elements are identified by names and chemical symbols.
• Atoms have a structure that determines their properties.
• Every atom is composed of three types of subatomic particles:
protons, neutrons, and electrons.
• The number of electrons in the outer shell of an element’s atoms
determines the properties of the element.
Ch. 2
CHAPTER
6
• The Periodic Table organizes elements in different ways.
• Metals are found on the left,
non-metals on the right,
and metalloids in between.
• Chemical families are arranged
in vertical groups.
• Periodic Tables can indicate the chemical symbol, atomic number, atomic
mass, ion charge, density, and other information about each element.
Ch. 2
• Elements are listed in order by atomic number
– Rows of elements (across) are called periods.
– All elements in a family have similar properties,
and bond with other elements in similar ways
•
•
•
•
Ch. 2
Group 1 = alkali metals
Group 2 = alkaline earth metals
Group 17 = the halogens
Group 18 = noble gases
CHAPTER
6
Ch. 2
6.1
VOCABULARY
• Physical properties can be observed
without changing the chemical
structure of a substance.
physical properties
chemical properties
mixtures
pure substances
elements
atoms
compounds
• Chemical properties describe a
possible chemical
change.
Ch. 2
6.2
The Nucleus
Ch. 2
Atomic Theory
VOCABULARY
subatomic particles
nucleus
protons
neutrons
atomic number
mass number
atomic mass
electrons
electron shells
unpaired electrons
paired electrons
Ch. 2
Atomic Theory
Name
Symbol
Charge
Location
Relative Mass
Proton
p
1+
nucleus
1836
Neutron
n
0
nucleus
1836
Electron
e
1–
area surrounding
the nucleus
1
Ch. 2
6.2
• Every atom of any one element will have the same
number of protons
• Atomic number = # of protons = # of electrons
• There are an equal number of protons and
electrons in an atom.
• Ions form when the number of electrons changes.
• The number of electrons in the outer shell
determines the properties of the element.
Ch. 2
Bohr Diagrams
• Bohr diagrams show how many electrons
appear in each electron shell around an atom.
– Each shell holds a maximum number of electrons
– 2 electrons in the first shell, 8 in the 2nd shell, and 8
in the 3rd shell.
– Electrons in the outermost shell are called valence
electrons
– Think of the shells as being 3D like spheres, not 2D
like circles
Ch. 2
– The period # = # of shells in the atom.
– Except for the transition elements,
the last digit of the group # = # of
electrons in the valence shell
Ch. 2
Bohr Diagrams
What element is this?
Ch. 2
Bohr Diagrams
•It has 2 + 8 + 8 = 18
electrons, and
therefore 18 protons
•It has 3 electron
shells, so it is in
period 3
•It has 8 electrons in
the outer (valence)
shell
Ch. 2
18 p
22 n
Argon!
Patterns of Electron Arrangement
in Periods and Groups
 The noble gas elements have full electron shells,
and are very stable.
Ch. 2
The Periodic Table
INCREASING REACTIVITY
Where are the
following?
• Atomic
Number
• Period
• Group/Family
• Metals
• Non-metals
• Transition
metals
• Metalloids
• Alkali metals
• Alkaline earth
metals
• Halogens
• Noble gases
Ch. 2