Chemistry
Chapter 8
Notes #1
Ions
Compounds

2 or more elements combined



Example: Sodium + Chlorine = Sodium
Chloride (which is table salt)
A compounds properties are different from the
properties of the individual elements that
make it up
Compounds can be represented by chemical
formulas

Ex. NaCl (salt)
Compounds

Compounds are held together by chemical
bonds
 Attractive forces that hold atoms or ions
together
 Ionic (referred to as formula units)
 Metallic
 Covalent (referred to as molecules)
Valence Electrons …
The electrons responsible for the
chemical properties of atoms, and are
those in the outer energy level.
 Valence electrons - The s and p electrons
in the outer energy level
 the highest occupied energy level
 Core electrons –the inner electrons
(those in the lesser energy levels)

Valence Electrons …

Atoms in the same column...


Have the same outer electron
configuration.
Have the same valence electrons.
The number of valence electrons are
easily determined: the group number
for a representative element
 Group 2A: Be, Mg, Ca, etc.


have 2 valence electrons
Electron Dot diagrams …





A way of showing & keeping
track of valence electrons.
How to write them?
Write the symbol - it
represents the nucleus and
inner (core) electrons
Put one dot for each valence
electron (8 maximum)
They don’t pair up until they
have to (Hund’s rule)
X
Electron Dot diagrams …
Nitrogen has 5 valence
electrons to show.
 First we write the symbol.

Then
N
add 1 electron at a
time to each side.
Now they are forced to pair up.
We have now written the electron dot
diagram for Nitrogen.
Stable Electron Configurations
All atoms react to try and achieve a noble
gas configuration.
 Noble gases have 2 s and 6 p electrons.
 8 valence electrons = already stable!
 This is the octet rule (8 in the outer level
is particularly stable).

Ar
Ions
Ions – atoms that have lost or gained
valence electrons, resulting in an overall
charge
 They lose or gain to meet the octet rule


Cations – positive ions (loss of electrons)


Metals form positive ions
Anions – negative ions (gain of electrons)

Nonmetals form negative ions
Cations



Form when metals lose electrons
Trying to meet the octet rule-Achieve a noble gas
configuration
Ex. Sodium (Na) becomes Na+
 Loses its 1s electron- Then has the same electron
configuration as Neon
Cations

calcium has only 2 valence electrons

It’s easier to lose 2 than gain 6
+2
Ca Ca
Cations

Example

Magnesium = 1s22s22p63s2
Mg+2
= 1s22s22p6
Neon
= 1s22s22p6

Drawings


cations
Cations

Transition Metals
 Most of the time will have a +2 or +3
charge
 They lose both electrons from their
outermost s sublevel
 Then, they can also lose inner unpaired d
sublevel e Which leads to a charge of more than +2

Pseudo noble gas configurations (Non octets with stability)
 Example: A pseudo-noble gas configuration is: 1s2
2s2 2p6 3s2 3p6 3d10 (and they have 2 in 4s)
 This is found in Cu+
Zn2+ Ga3+ and Ge4+
Anions
Nonmetals will have many valence
electrons (usually 5 or more)
 They will gain electrons to fill outer shell.

P
3P
This is called the
phosphide ion
Electron Configurations for Anions

Example




Oxygen
O-2
Neon
= 1s22s22p4
= 1s22s22p6
= 1s22s22p6
Drawings
Oxygen
Ions
Polyatomic Ions
Al individual elements that have lost or
gained electrons are monatomic ions
 Binary compound – 2 monatomic ions
combine
 Oxidation Number – the charge of the ion
 Polyatomic ions – a group of more than 1
atom that loses and gains electrons




They act like an individual ion
Have one charge (as a unit)
Oxyanions = polyatomics with oxygen