Download Note - Science 10

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, 8, 8, 18, 18)
 Electrons in the outermost shell are called
valence electrons
 If the valence shell is full = the atom is stable
 If the valence shell is not full = the atom is not
stable
Note: Think of the shells as being 3D like spheres, not 2D like circles!
Bohr Diagrams
What element is this?
• It has 18 protons and it
has 2 + 8 + 8 = 18
electrons.
18 p
22 n
•It has 8 electrons in the
outer (valence) shell
Argon!
Bohr Diagrams for the first 20 elements
 Note: The noble gas
elements have full electron
shells, and are very stable.
Bonding Types:
 When two atoms get close together, their
valence electrons interact.
Ionic Bonds:
 Metals give electrons to non-metals (transfer of
valence electrons)
 cations (+ ions) and anions (- ions) form
 For example, lithium and oxygen form an ionic
bond in the compound Li2O
+
Lithium
Oxygen
Electrons are transferred from
the cations to the anion
Li+
O2Li+
Lithium oxide,
Li2O
 Bohr Diagram for LiF - Lithium fluoride
On board
Covalent Bonds:
 Formed between two or more non-metals
 Valence electrons are shared between atoms
 A group of covalently bonded atoms are called a
molecule
+
Hydrogen
Hydrogen fluoride
Fluorine
Electrons are shared
 Bohr Diagram for CH4 – Methane (or
carbon tetrahydride)
On Board
Lewis Diagrams:
 Like simplified Bohr diagrams
 Only valence electrons are shown
 Dots representing electrons are placed around
the element symbols (on 4 sides, imagine a box
around the symbol)
 Electron dots are placed singularly, until the fifth
electron is reached, then they are paired.
Example:
Nitrogen atom
Lewis Diagrams:
 Note: the Lewis diagrams are the same
(except for the symbols) for elements in the
same family because they have the same
number of valence electrons
Lewis Diagrams for Ions:
 For positive ions: one electron dot is removed
from the valence shell for each positive charge
of the ion.
 For negative ions: one electron dot is added to
each valence shell for each negative charge of
the ion.
 Square brackets and the charge are placed
around each ion
Example:
Nitrogen ion
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
•
Lewis Diagrams For Ionic Bonds:
–
•
••
• •
•
•
Be
•
•
Cl
••
••
•
•
••
••
Each
beryllium has
two electrons to
transfer away, and
each chlorine wants
one more electron
•
•
Cl
••
••
••
Be
••
••
••
••
••
Cl
•
•
• •
Since Be2+ wants to
donate 2 electrons and
each Cl– wants to accept
only one, two Cl– ions are
necessary
•
•
Cl
••
••
•
••
Be
•
•
••
2+
••
•
–
••
Cl
•
•
••
The ionic compound
Beryllium chloride is
formed