Chemistry 1 from 3
Chapter 1 MATTER
RELATIVE ATOMIC MASS (RAM)It is the weighted mean of the mass of constituent isotopes, taking an account the relative abundance of each isotope.
Example: Calculate the RAM of Chlorine if it’s isotopic abundance is 75% for 1735Cl
and 25% for1737Cl
.
Solution
RAM=75100*35+25100*37=35.5
Electronic Configuration (Ec)
This is the arrangement of electrons on the shells of an atom.
The 1st shell = K shell and takes a maximum of 2 electrons
The 2nd shell = L shell and takes a maximum of 8 electrons
The 3rd shell = M shell and takes a maximum of 8 electrons
The 4th shell = N shell and takes a maximum of 18 electrons
The 5th shell = O shell and takes a maximum of 8 electrons
The 6th shell = P shell and takes a maximum of 8 electrons
|
|
Example 24Be
has the electronic configuration
|
Elements |
Atomic Number |
Electronic Configuration |
|
H |
1 |
1 |
|
Li |
3 |
2:1 |
|
Mg |
12 |
2:8:2 |
|
K |
19 |
2:8:8:1 |
Groups and Electronic Configuration
Lithium (Li), Sodium (Na) and Potassium (K) all has one electron in their outermost shell (valence shell). So they are found in group 1.
Magnesium (Mg) and Calcium (Ca) has two electrons in their outer most shell (valence shell) and are found in group 2.
Fluorine (F), Chlorine (Cl), Bromine (Br) all have seven electrons in their outermost shell and are found in group 7.
Therefore, the number of electrons in the outermost shell tells us the group to which the element belongs.
|
Element |
Symbol |
Atomic Number |
Electronic Configuration |
|
Hydrogen |
H |
1 |
1 |
|
Helium |
He |
2 |
2 |
|
Lithium |
Li |
3 |
2.1 |
|
Beryllium |
Be |
4 |
2.2 |
|
Boron |
B |
5 |
2.3 |
|
Carbon |
C |
6 |
2.4 |
|
Nitrogen |
N |
7 |
2.5 |
|
Oxygen |
O |
8 |
2.6 |
|
Fluorine |
F |
9 |
2.7 |
|
Neon |
Ne |
10 |
2.8 |
|
Sodium |
Na |
11 |
2.8.1 |
|
Magnesium |
Mg |
12 |
2.8.2 |
|
Aluminum |
Al |
13 |
2.8.3 |
|
Silicon |
Si |
14 |
2.8.4 |
|
Phosphorus |
P |
15 |
2.8.5 |
|
Sulphur |
S |
16 |
2.8.6 |
|
Chlorine |
Cl |
17 |
2.8.7 |
|
Argon |
Ar |
18 |
2.8.8 |
|
Potassium |
K |
19 |
2.8.8.1 |
|
Calcium |
Ca |
20 |
2.8.8.2 |
It is the weighted mean of the mass of constituent isotopes, taking an account the relative abundance of each isotope.
Example: Calculate the RAM of Chlorine if it’s isotopic abundance is 75% for 1735Cl and 25% for1737Cl.
Solution
RAM=75100*35+25100*37=35.5
Electronic Configuration (Ec)
This is the arrangement of electrons on the shells of an atom.
The 1st shell = K shell and takes a maximum of 2 electrons
The 2nd shell = L shell and takes a maximum of 8 electrons
The 3rd shell = M shell and takes a maximum of 8 electrons
The 4th shell = N shell and takes a maximum of 18 electrons
The 5th shell = O shell and takes a maximum of 8 electrons
The 6th shell = P shell and takes a maximum of 8 electrons
|
|
Example 24Be has the electronic configuration
|
Elements |
Atomic Number |
Electronic Configuration |
|
H |
1 |
1 |
|
Li |
3 |
2:1 |
|
Mg |
12 |
2:8:2 |
|
K |
19 |
2:8:8:1 |
Groups and Electronic Configuration
Lithium (Li), Sodium (Na) and Potassium (K) all has one electron in their outermost shell (valence shell). So they are found in group 1.
Magnesium (Mg) and Calcium (Ca) has two electrons in their outer most shell (valence shell) and are found in group 2.
Fluorine (F), Chlorine (Cl), Bromine (Br) all have seven electrons in their outermost shell and are found in group 7.
Therefore, the number of electrons in the outermost shell tells us the group to which the element belongs.
|
Element |
Symbol |
Atomic Number |
Electronic Configuration |
|
Hydrogen |
H |
1 |
1 |
|
Helium |
He |
2 |
2 |
|
Lithium |
Li |
3 |
2.1 |
|
Beryllium |
Be |
4 |
2.2 |
|
Boron |
B |
5 |
2.3 |
|
Carbon |
C |
6 |
2.4 |
|
Nitrogen |
N |
7 |
2.5 |
|
Oxygen |
O |
8 |
2.6 |
|
Fluorine |
F |
9 |
2.7 |
|
Neon |
Ne |
10 |
2.8 |
|
Sodium |
Na |
11 |
2.8.1 |
|
Magnesium |
Mg |
12 |
2.8.2 |
|
Aluminum |
Al |
13 |
2.8.3 |
|
Silicon |
Si |
14 |
2.8.4 |
|
Phosphorus |
P |
15 |
2.8.5 |
|
Sulphur |
S |
16 |
2.8.6 |
|
Chlorine |
Cl |
17 |
2.8.7 |
|
Argon |
Ar |
18 |
2.8.8 |
|
Potassium |
K |
19 |
2.8.8.1 |
|
Calcium |
Ca |
20 |
2.8.8.2 |