Learning check
Once you have watched the video, check your learning with this quiz.
Dmitri Mendeleev
- Middle of the 19th century: Some 60 elements discovered.
- Mendeleev organizes them by atomic mass.
An early periodic table.
Dmitri Mendeleev.
Groups and periods
In a modern periodic table, the atoms are ordered by atomic number.
The groups of the periodic table are the vertical ↓ columns. The atoms in the same group contain the same number of valence electrons.
The periodic table.
The periods of the periodic table are the horizontal → rows. The atoms in the same period contain the same number of electron shells.
Trends in the periodic table
Trends in the periodic table. The arrows show an increase in the specified character.
Metals are generally to the left of the periodic table, nonmetals to the right.
The size (atomic radius) decreases as we move to the right of the periodic table
- Increased nuclear charge ⇒ electrons tighter around the nucleus.
Reactivity increases downward in groups 1 and 2 because of lower ionization energy.
Reactivity increases upward in groups 16 and 17 because of higher electron affinity.
To learn by heart
| Name | Group | Number of valence electrons |
| Alkali metals | 1 | 1 |
| Alkaline earth metals | 2 | 2 |
| Boron group | 13 | 3 |
| Carbon group | 14 | 4 |
| Nitrogen group | 15 | 5 |
| Oxygen group | 16 | 6 |
| Halogens | 17 | 7 |
| Noble gases | 18 | 8 (He: 2) |
