Download available here

Atomic Structure and Bonding
Week 2





Atomic structure and bonding related to
properties of materials
Nuclide notation. Isotopes and relative atomic
mass. Ions. Ionic bonding.
Covalent molecular, covalent network and
ionic lattices.
Physical properties of chemicals explained
through bonding.
Chemical and ionic formulae including group
ions.
1st electron shell
holds 2 electrons

2nd electron shell
holds 8 electrons

3rd Electron shell
holds 8 electrons

REMEMBER THE NUCLEUS
HAS A
POSITIVE CHARGE
Subatomic
particle
Proton
Neutron
Electron
Position
in atom
Charge
Mass
In
nucleus
In
nucleus
Outside
nucleus
1+
1
No
charge
1-
1
0

Is overall Neutral
◦ Because has the same number of positive protons
and negative electrons


Different elements have different number of
protons
Recognised as an ATOMIC NUMBER

Unique for every element

Equals the
◦ Number of protons
◦ Number of electrons (for an atom)

The only two particles which have mass in an
atom are
◦ Protons
◦ Neutrons
BOTH ARE FOUND IN
NUCLEUS

The only two particles which have mass in an
atom are
◦ Protons
◦ Neutrons

BOTH ARE FOUND IN
NUCLEUS
MASS NUMBER =
◦ PROTONS + NEUTRONS

NO. OF NEUTRONS =
◦ MASS NUMBER – ATOMIC NUMBER

Number of protons = never changes
◦ Is like the elements DNA, will never change

Number of neutrons = affect mass of atom
◦ Some heavier, some lighter atoms

Number of electrons = affects the mood the
element in
◦ Neutral
◦ Positive
◦ Negative
Note the numbers are
written at LHS of symbol



Atomic Number is at the bottom – can be
checked using data book if you forget
Mass Number (the bigger number) at the top.

No. of protons = Atomic Number
◦ = 17

No. of electrons = Atomic Number
◦ = 17

No. of neutrons = Mass No. – Atomic No.
◦ = 37- 17 = 20

Are atoms with the
◦ Same atomic number
◦ But, Different mass number
 i.e. Different number of neutrons

Most elements exist as a mixture of isotopes

This is rarely a whole number
◦ WHY?

The relative atomic mass is an average of all
the different Isotopes taking into account the
proportion of each present.

Relative Atomic Mass = 36.5

Would expect Average to be = 36

Closer to 37 = Grater proportion of 37
isotope present


Relative Atomic Mass = 36.0
This tells you that there is exactly 50% of
each isotope present as the average lies
exactly in the middle.

Charged particles

Group 1 – Alkali Metals
◦ Reactive

Group 7 – Halogens
◦ Reactive

Group 8 (0) – Nobel gases
◦ Unreactive


Atoms held together by bonds
Bonds are formed so elements can achieve a
stable electron arrangement
◦ i.e. a full outer shell like the noble gas elements.
REMEMBER GROUP 8 ARE UNREACTIVE AND SO
NOT BOND

Non-metals only

Atoms share electrons

Covalent bond held together by
◦ Attraction between the positive nuclei and the
negative shared electrons

Molecule = group of atoms held together by
COVALENT bonds

2 elements bonded together

Diatomic Elements
◦ H, N, O, F, Cl, Br, I

Diatomic Compounds
◦ CO, NO



Low Mp and Bp
Because strong
covalent bonds not
broken
Weak forces BETWEEN
molecules broken
MOLECULAR
High Mp and Bp
 Because strong
covalent bonds need to
be broken and this
required a lot of
energy.
 E.g.
Diamond
Sand (SiO2)

NETWORK

(usually) soluble in non-aqueous solvents
(usually) insoluble in aqueous solvents(water)

NEVER CONDUCT ELECTRICITY!!!!

Try
CH4
NH3
HCl
CO2 – very tricky!

Charged Particle

Metals – lose electrons – form +ve Ions
MP

Non-metals – gain electrons – form –ve Ions


Between metals and non-metals
Bond held together by electrostatic attraction
between POSITIVE AND NEGATIVE IONS
Crystal Lattice
Structure of
oppositely
charged ions



Do not conduct when solid as
IONS NOT FREE TO MOVE
Conduct when in solution or molten as
IONS ARE FREE TO MOVE
Solid at room temperature
◦ Strong forces of attraction that need to be broken

Soluble is aqueous solvent (i.e. water)