ZON PENA

The period

• Period is the horizontal rows of elements in the Periodic Table.
• The modern periodic table has 7 periods.
• The period number indicates the number of electron shell.
• Elements in the same period have same number of electron shells.
• The proton number of elements increases from left to right crossing the period.
• The number of electrons is also increases from left to right crossing the period.

Physical Change Across a Period

• There are a few major changes in physical properties across a period.
• For example,

1. the state of matter changes across the period.
2. The size of the molecule changes across the period, too.

State of Matter

• The diagram above shows that the state of matter of the elements in period 2 and period 3 change from solid to gas across the period (At room temperature).
• In period 2, the first 4 elements are solid whereas the last 4 elements are gases. The melting point of lithium is low while the melting point of boron and carbon is very high.
• In period 3, the first 6 elements are solid whereas the last 2 elements are gases. In fact, it is very difficult to find elements exist as liquid state at room temperature. The only one that I know is bromine.

Atomic Size

• As shown in the diagram above, the atomic size of elements in period 2 and period 3 decreases across a period.
• This is because

1. The number of proton in the nucleus increases whereas the number of electron shell remain unchanged across a period.
2. As the number of proton in the nucleus increases, the positive charge of the nucleus will also increases.
3. The negative charge of the valence electrons will also increases due to the increase of number of valence electrons across a period.
4. Thus, the attraction force between the nucleus and the valence electrons is getting stronger and stronger across a period.
5. This force will pulls the valence electrons closer to the nucleus and thus reduces the atomic radius.
6. Therefore the size of atom decreases across a period from left to right.

• Diagram below shows the change of the atomic size of the elements in all seven period. The trends can be conclude as below:

1. The size of atom increases down the group.
2. The size of atom decreases across a period from left to right.
3. For transition metal, the size of atom does not has obvious change across a period.

Chemical Properties Change Across a Period

• There is gradual chemical change across a period.

1. The acidity (or basicity) of the oxide of element changes across a period.
2. The metallic property, the electronegativity of element also change across a period.

Acidic Oxide or Basic Oxide

1. From left to right across a period the oxides change from alkaline/basic (with metals e.g. Na2O) to acidic (with non-metals e.g. SO2).

Metal, Metalloid and Non-metal

Metal and Non-metal

• As we go across a period from left to right, the elements change from metals to non-metals.
• Most of the known elements are metals.
• Only about 19 elements in the periodic table are non-metal.
• There are about 7 elements in the periodic table are classified as semi-metals.
• The metals in the periodic table are mainly found in the left hand columns (Groups 1 and 2) and in the central blocks of the transition elements.
• On the right hand side of the periodic table, there are 7 semi-metals (blue colour) form a staircase like pattern, act as a divider between metal and non-metal.
• The semi-metals are also called the metalloid.
• All the elements on the right hand side of the staircase are non-metals.

Uses of Metalloids

• The most widely used semi-metals are silicon and germanium.
• It is used to make diodes and transistors in electronic industry.
• Discussion of electronic can be found in SPM form 5 Physics.

Electronegativity

• Electronegativity is a measure of the potential of atoms to attract electrons to form negative ions.
• It is indicated bya number between 0 and 4.0. For example, the electronegativity of fluorine is 3.98 and the the electronegativity of sodium is 0.93.
• Metals have low electronegativities.
• Non-metals have high electronegativities.
• Electronegativities of the elements increase across a period with increasing proton number. This is because

1. as the proton number increases, the positive charge of the nucleus will increase accordingly.
2. this will increase the ability of the atom to attract electrons from the surrounding and thus increase the electronegativity of the atom.

• The table in the external link provided below shows the electronegativity of elements in periodic table. Nevertheless, the electronegativities of each elements are not important in SPM syllabus.