Transcript Atoms and Ions

Atoms and Ions
SNC2D
The Bohr-Rutherford Model
Helium Atom
• 2 positive protons
in nucleus
• 2 neutral neutrons
in nucleus
• 2 negatively
charged electrons
in the first energy
level
Standard Atomic Notation
(for a neutral atom)
Atomic symbol
Mass number
80
35
Atomic number
Br
Number of
protons
Atomic
number (35)
35 p+
Number of
electrons (for
neutral atom)
Atomic
number (35)
35 e-
Number of
neutrons
Mass number
– Atomic
number
(80-35=45)
45 n0
Neutral Atoms and Ions
• When using standard atomic notation
you can assume the atom is neutral and
the number of electrons is equal to the
number of protons
• A charge is shown if it is an ion.
80
35
Br
1–
Ionic charge
(1 extra electron)
Terms to Know
• Valence
– The combining capacity of an element
• Valence shell
– The outer electron shell of an atom, the electrons
in this shell are called valence electrons
• Isoelectric with a noble gas
– The same number of electrons as a noble gas
Ions
• Many elements want to form stable ions
where the number of electrons in the
valence shell is the same as a noble gas.
• Metals tend to become positively charged
cations.
• Non-metals tend to become negatively
charged a n i o n s .
• They become ions by gaining or losing
electrons (which ever is easier).
The Why of Ions
The Noble Gases do not react and do not
form ions because they already have
what all atoms want: full outer shells.
Anions
1Cl
Cl
• Easier to gain 1 electron than lose 7.
• Therefore the atom becomes an anion by gaining an electron.
• It becomes more stable by gaining an electron. It becomes iso-electric
with Ar.
Cations
1+
Na
Na
• Easier to lose 1 electron than gain 7.
• Therefore the atom becomes a cation by losing an electron.
• It becomes more stable by losing an electron. It becomes iso-electric
with Ne.
The How of Ions
Non-metals, when they form ions,
change their names to:
the first syllable + the suffix “ide”
Anion names
chlorine
fluorine
bromine
oxygen
sulphur
nitrogen
phosphorus
Valence Practice
Given the following Bohr diagram, what
will the valence of the ion be?
TRY THESE
1. Name these ions: [K]
a)
Mg2+
b) S2-
c) Br-
d) N3-
2. List three atoms or ions that have the same number
of electrons as each of the following: [I]
a)
Al3+
b) P3-
c) Kr
d) Cs+
3. Suppose that a new element has been made.
Chemical tests show that it is an alkaline earth
metal. [I]
a)
b)
Predict how many electrons there will be in the outer orbit.
Predict the ionic charge of the ion that this element forms.
4. Justify why these ions do not exist under normal
conditions. [A]
a)
K2+
b) O-
Credits
•
http://commons.wikimedia.org/wiki/File:Helium-Bohr.svg