Chemistry Topic: Properties of Groups in the Periodic Table and Particles Of The Atom

The periodic table contains vertical columns called groups and horizontal rows called periods. Elements in the same group generally have the same number of electrons in their outermost shell (valence electrons). This gives them similar chemical properties.

The number of valence electrons helps determine how an element reacts with other elements and the ions it can form.

Properties of Periodic Table Groups

In the older group classification used in many secondary school chemistry textbooks, the main groups are represented as Groups I, II, III, IV, V, VI, VII and O.

Note: In the modern periodic table, these groups correspond to Groups 1, 2, 13, 14, 15, 16, 17 and 18 respectively.

Helium has only two electrons in its outermost shell, but it is placed in Group O (modern Group 18) because its only electron shell is complete. Other noble gases have eight electrons in their outermost shells.

Properties of Periods in the Periodic Table

The horizontal rows of the periodic table are called periods.

Elements in the same period have the same number of occupied electron shells. For example, elements in Period 2 have two occupied electron shells, while elements in Period 3 have three.

Classification of Elements into Groups

The main groups in the older classification are:

1. Group I
2. Group II
3. Group III
4. Group IV
5. Group V
6. Group VI
7. Group VII
8. Group O

Some Questions on the Properties of Groups in the Periodic Table

1. Explain the discovery of the electron by J. J. Thomson.
2. Explain the discovery of positive rays by Eugen Goldstein and the identification of the proton by Ernest Rutherford.
3. Explain the properties of elements in Groups I, II, III, IV and O.

Solution 1: Discovery of the Electron by J. J. Thomson

J. J. Thomson discovered the electron in 1897 through experiments using a cathode ray tube. He passed an electric current through a gas at very low pressure and observed rays travelling from the cathode towards the anode.

The rays were called cathode rays. His experiments showed that they consisted of negatively charged particles, which were later called electrons.

The characteristics of cathode rays include:

1. They travel in straight lines, as shown by the shadows they cast when opaque objects are placed in their path.
2. They are deflected towards the positive plate in an electric field, showing that they carry negative charges.
3. They are also deflected by magnetic fields.
4. They carry energy and can cause certain substances to glow.

Solution 2: Discovery of Positive Rays and Identification of the Proton

Discovery of positive rays

Eugen Goldstein discovered positive rays, also called canal rays, in 1886. He used a discharge tube fitted with a perforated cathode. He observed rays travelling in the opposite direction to cathode rays and passing through the holes in the cathode.

The characteristics of positive rays include:

1. They travel in straight lines.
2. They carry positive charges.
3. They are deflected towards the negative plate in an electric field.
4. Their particles have different masses depending on the gas used in the discharge tube.

Identification of the proton

Ernest Rutherford identified the hydrogen nucleus as a positively charged particle called the proton through his nuclear experiments. The proton has a positive charge equal in magnitude to the negative charge of an electron.

Solution 3: Properties of Groups I, II, III, IV and O

Properties of Groups I, II and III

1. Elements in Groups I, II and III generally have one, two and three electrons respectively in their outermost shells.
2. Most of these elements are metals and tend to lose their outermost electrons during chemical reactions.
3. When they lose electrons, they form positively charged ions called cations.
4. They are generally electropositive because they tend to donate electrons.
5. Elements in the same group usually have similar chemical properties.

Examples:

• Group I: Lithium, sodium and potassium.
• Group II: Magnesium, calcium and barium.
• Group III: Aluminium and gallium. Boron is an exception because it is a metalloid.

Properties of Group IV Elements

1. Elements in Group IV have four electrons in their outermost shells.
2. They may form covalent bonds by sharing electrons with other atoms.
3. Their chemical properties vary because the group contains non-metals, metalloids and metals.
4. Carbon is a non-metal, silicon and germanium are metalloids, while tin and lead are metals.
5. They do not all gain or lose four electrons to form ions.

Properties of Group O Elements

Group O elements are also called noble gases or inert gases. Examples include helium, neon, argon, krypton, xenon and radon.

Their properties include:

1. They have complete outermost electron shells.
2. Helium has two electrons in its outermost shell, while the other noble gases have eight.
3. They have stable electronic configurations.
4. They are generally unreactive because their outermost electron shells are complete.
5. They exist as single atoms under normal conditions.
6. They are colourless gases at room temperature.
7. Some noble gases, such as xenon, can form compounds under special conditions.

Related Articles:

• Calculation of Isotopes and Relative Atomic Mass in Chemistry
• Definition of Isotopes and Relative Atomic Mass (Solutions)