Unit 2
From atoms to molecules
Periodic Table:
Electronic configuration
Chemistry MYP4 2021/22
n° neutrons + n° protons (+) =
Mass Number
Atomic Number =
n° protons (+) = n° electrons (-)
(is the number on the periodic table)
The Atom is made of subatomic particles:
- Protons: in the nucleus, positive charge
- Neutrons: in the nucleus, no charge
- Electrons: moving around the nucleus, negative charge
Mass​
1,672 × 10-24 g​
0,000000000000000000000001672 g
1,672 × 10-24 g​
0,000000000000000000000001672 g
9,109 × 10-27 g​
0,000000000000000000000000009109 g
Since the mass value of the electrons (-) is negligible versus
the mass value of the other particles, the mass in the atom is
given only by the particles in the nucleus: protons (+) and neutrons.
Rutheford model (planetary model)
The electrons are moving in orbits around the nucleus and the orbits are at a fixed
distance from the nucleus (defined also as "shells")
In the very 1st shell, there could be only 2 electrons.
And there are 8 electrons for any other shell starting from the 2nd one.
​Electrons in the most external
orbit (outer shell) are very important to deter
mine chemical and physical properties.​
Electrons in the outer shell are
called VALENCE ELECTRONS.​
The number of electrons/protons is increasing one by one along
the periodic table from left to right and row by row.​​
Elements in
the same group have the same valence electron number (represented by the
number of the group)
Periodic table
The periodic table arranges all the elements in groups according to
their properties.
The horizontal rows are called periods and are labeled from 1 to 7.
The vertical columns are called groups are labeled from 1 to 8 (or 18).
G
r
o
u
p
It is like playing Battleship!
period
Hydrogen
1 electron (-)
1 proton (+) in the nucleus
Only one shell
1st shell is the outer shell
One electron in the outer shell
Period 1
Group 1
He - Helium
2 electrons (-)
2 protons (+)
2 neutrons
in the nucleus
Only one shell
Two electron in the outer shell
1st shell is the outer shell and it
is full
Period 1
Group 8
Exception!
It should be group 2 but...
It goes in Group 8 because it is the group with
full outer shells
3 electrons (-)
3 proton (+)
4 neutrons
Li - Lithium
in the nucleus
Z = Mass Number = 7
Two total shells.
One electron in the outer shell.
Three total electrons.
Period 2
Group 1
A = Atomic number = 3
4 electrons (-)
Be - Berillium
4 protons (+) in the nucleus
5 Neutrons
Z = Mass Number = 9
Two total shells.
Two electron in the outer shell.
Four total electrons.
Period 2
Group 2
A = Atomic number = 4
5 electrons (-)
B - Boron
__ Protons (+) in the nucleus
__ Neutrons
?
Z = Mass Number =
Two total shells.
Three electron in the outer shell.
Five total electrons.
Period 2
Group 3
A = Atomic number =
?
5 electrons (-)
B - Boron
5 Protons (+) in the nucleus
6 Neutrons
Z = Mass Number = 11
Two total shells.
Three electron in the outer shell.
Five total electrons.
Period 2
Group 3
A = Atomic number = 5
6 electrons (-)
C- Carbon
__ Protons (+) in the nucleus
__ Neutrons
?
Z = Mass Number =
Two total shells.
Four electron in the outer shell.
Six total electrons.
Period 2
Group 4
A = Atomic number =
?
HOMEWORK
Design at the same way the electronic
configuration of the atoms
from Nitrogen to Magnesium
Symbols
Na Sodium (from Natrium, lat.)
K Potassium (from Kalium, lat.)
Cu Copper (from Cuprum, lat. "from Cyprus", where the major part of this
metal was extracted at the time)
Au Gold (from Aurum, lat.)
Ag Silver (from Argentum, lat.)
Pb Lead (from Plumbum, lat.)
Hg Mercury (from Hydrargirium, gr. "silver water")
W Tungsten (from Wolframio/Wolf ram, ted. "wolf black" or Tung sten, sved.
"heavy stone")
Sb Antimony (from Stibium, lat. "stick")
Formula
one or more symbols with numerical subscripts that represents the single unit
atomic composition of the fundamental particle that makes up the substance.
Elements:
Monatomic: The formula is the same as the symbol, eg. He, Ar, Na.
Diatomic: When the natural form in which the element exists is made by two
atoms of the same element: H2, O2, N2, Cl2, F2, I2, Br2
Compounds:
Formula is given by the symbols of each atom in the molecule together with
numerical subscripts that mean the quantity of each atom forming the
molecule.
e.g.
CO2 = one atom of Carbon and two atoms of Oxygen
Classification
Elements are classified in three big families:
Metal
Metalloid/Semi
metal
Non-metal
The physical and chemical properties depend on the valence of the
elements.
The valence of the elements is the number electrons that the atom has on
the outer shell and is directly connected to the number of bonds that
the atom is able to form with a standard element and it is closely
correlated with position in the periodic table.
Elements are divided in groups by their valence electrons number
Groups
Alkali Metals
Alkaline Earth Metals
1st column on the periodic table
(Group 1) not including hydrogen.
Second column on the periodic table.
(Group 2)
Very reactive metals, always
combined with something else in
nature (like in salt).
Reactive metals that are always
combined with nonmetals in nature.
They form cations (positive ions)
Soft metals with low melting points
They BOTH form compounds with alkaline properties (Hydroxides).
Most reactive elements together with Group 7 Halogens.
Several of these elements are important mineral nutrients (such as Na, K, Mg and
Ca) very important for the maintenance and regulation of the body physiology.
Halogens
The Noble Gases
Elements in group 8 have a full
valence shell.
monatomic gases
Elements in group 7.
Very reactive, volatile, diatomic,
nonmetals
Always found combined with other
element in nature.
They form anions (negative ions)
Transition Metals
VERY stable, inert = unreactive
(very suitable in applications where
reactions are not wanted)
(i.e. Used in lighted “neon” signs)
• good conductors of heat and electricity.
• they can be hammered or bent into shape
easily (ductility).
• high melting points (but mercury is a
liquid at room temperature)
• usually hard and tough.
• high densities.
Non Metals and semi-metals
Group 3
Boron is commonly classified as a (metalloid) while the
rest are considered post-transition metals.
Carbon family. Carbon is the building block of organic
chemistry together with Hydrogen. Silicon and
Germanium are important semiconductors.
Group 5
Group 4
Nitrogen family. Nitrogen is the main component of the air
together with Oxygen (78% and 20%) and Argon, CO2, etc…
The tip of matches is made of phosphorus.
Oxygen family. Elements of this group are called
"chalcogens" that means "ore formers" from the greek.
Selenium has some biological functions (in aminoacids)
but it is also toxic. Tellurium and Polonium are toxic
too; Polonium has also a radioactive isotope.
Group 6