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4.1 Atomic Theory & Bonding
ATOM: smallest particle of an element, has a neutral charge.
PEN = proton(s) + electron(s) + neutron(s)
ELEMENT: made up of 1 type of atom (eg.oxygen O)
IONS: atoms with charges (eg. oxygen is O2-)
MOLECULES: groups of covalently bonded atoms (eg. oxygen molecules are O2)
COMPOUNDS: are made up of at least 2 atoms bonded together.
Hydrogen and oxygen are atoms/elements
H2O is a compound
Structure of an Atom:
Name Symbol Charg
e Location
Atomic
Mass
Proton p 1+ nucleus 1 AMU
Neutron n 0 nucleus 1 AMU
Electron e 1– area surrounding
the nucleus 1/1836 (0)
Numbers to Remember :
Protons = Atomic Number
Neutrons = Mass number – Atomic number (Mass # - proton #).
Neutrons + Protons = Mass #
Electrons in an atom = atomic number (also proton #)
Electrons in an ion = atomic number – ion charge
Families of the Periodic Table:
Columns of elements are called groups, or families
All elements in a family have…
similar properties
bond with other elements in similar ways
have the same number of valence electrons
Family names (on the periodic table!):
Group 1 = alkali metals (1+, highly reactive)
Group 2 = alkaline earth metals (2+, reactive)
Group 17 = the halogens (1-, very reactive)
Group 18 = noble gases (0, unreactive)
Periods are horizontal rows on the periodic table.
INC
RE
AS
ING
RE
AC
TIV
ITY
Where are the
following?
• Atomic
Number
• Period
• Group/Family
• Metals
• Non-metals
• Transition
metals
• Metalloids
• Alkali metals
• Alkaline earth
metals
• Halogens
• Noble gases
Periodic Table & Ion Formation:
Ions: Atoms that gain and lose electrons to become
stable (full valence shells).
1. Cations: metals that lose electrons & form
positive ions (Na+)
Multivalent: Some metals can have more than
one charge (Fe2+ or Fe3+).
2. Anions: Non-metals gain electrons & form
negative ions (O-2)
Bohr Diagrams:
Bohr diagrams show how many electrons
appear in each electron shell around an
atom. (2, 8, 8, 18, 18)
Valence electrons: electrons in the outermost
shell ONLY.
If the valence shell is full = stable
If the valence shell is not full = reactive
What element is this?
Bohr Diagrams
•It has 2 + 8 + 8 = 18
electrons, and therefore
18 protons
•It has 8 electrons in the
outer (valence) shell
18 p
22 n
Argon!
Ionic Bonds:
Formed between Metals (cations) & non-metals (anions).
Valence electrons are transferred from metal to nonmetal.
Eg. Li2O
Lithium Oxygen
+
Electrons are transferred from
the cations to the anion Li+ O2- Li+
Lithium oxide,
Li2O
Formed between two or more non-metals
Valence electrons are shared between atoms
Eg. HF
Covalent Bonds:
Hydrogen Fluorine
+
Electrons are shared
Hydrogen fluoride
Lewis Diagrams:
Only valence electrons are shown
Dots representing valence electrons are placed around the element symbols (on 4 sides, imagine a box around the symbol)
Electron dots are placed singularly,
then they are paired.
Ex: Nitrogen
atom
Lewis Diagrams for Ions:
Ex. Nitrogen ion
Remove or add electron dots to
make full valence shells.
Square brackets and the charge
are placed around each ion
Be Cl
• •
• •
• •
• •
Each beryllium has two
electrons to transfer
away, and each chlorine
wants one more electron
Be Cl Cl • •
• •
• •
• •
• •
• •
• •
• •
• •
• •
• •
• •
Be Cl Cl • •
• •
• •
• •
• •
• •
• •
• •
• •
• •
• •
• •
Since Be2+ wants to
donate 2 electrons and
each Cl– wants to
accept only one, two Cl–
ions are necessary
The ionic compound
Beryllium chloride is
formed
2+ – • •
• •
• •
• •
–
Lewis Diagrams For Covalent Bonds:
valence electrons are drawn to show sharing of electrons.
Remember: All atoms “like” to have a full valence shell
The shared pairs (“bonding pairs”) of electrons are usually drawn as a straight line
“lone pairs” are the electrons not shared