Question

A common trend to both groups I and VII elements in the periodic table as the atomic number increases is (1) oxidising power increases (2) atomic radius increases (3) maximum valence increases (4) reactivity with water increases

Short answer

The atomic radius increases.

Step-by-step solution

Understand Group Trends

Group I elements are alkali metals and Group VII elements are halogens. Consider the general trends of these groups as the atomic numbers increase.

Consider Oxidising Power

Typically, the oxidising power of halogens (Group VII) increases as the atomic number decreases. This trend does not hold for both groups.

Evaluate Atomic Radius

As we move down either group in the periodic table, additional electron shells are added. This increases the atomic radius for both Group I and Group VII elements.

Assess Maximum Valence

Maximum valence is related to the group number and does not change as you move down a group. Hence, this trend does not increase with atomic number for either group.

Check Reactivity with Water

Group I metals become more reactive with water as the atomic number increases. However, Group VII elements do not generally react with water in the same way.

Conclusion

The only trend that holds for both groups as the atomic number increases is the increase in atomic radius.

Key concepts

Atomic Radius

The atomic radius refers to the size of an atom. It is the distance from the center of the nucleus to the outermost electrons. As you move down the periodic table in a group, the atomic radius increases for both Group I and Group VII elements.

Why does this happen? As you go down a group in the periodic table, each element has an additional electron shell compared to the one above it. This increase in the number of electron shells results in a larger atomic radius.

In simpler terms, think of each step down the group as adding another layer around the atom. The more layers, the bigger the atom gets!

• In Group I: Elements like lithium, sodium, and potassium get bigger as you move down the group.
• In Group VII: Elements like fluorine, chlorine, and bromine also increase in size as you go down the group.

So, the key trend to remember is: More shells mean a larger atomic radius.

Group I Elements

Group I elements in the periodic table are known as alkali metals. These include lithium, sodium, potassium, rubidium, cesium, and francium. They display several important trends:

Reactivity with Water
As you go down the group, alkali metals become more reactive with water. For example, potassium reacts more vigorously with water than sodium.

Increasing Atomic Radius
Just like we discussed, the atomic radius of alkali metals increases as you move down the group. This is due to the addition of electron shells.

Low Ionization Energy
Alkali metals have low ionization energies, which makes it easy for them to lose their single valence electron. This low ionization energy decreases further as you move down the group.

• Alkali metals have one electron in their outermost shell.
• They are highly reactive, especially with water.
• They are soft metals and can be cut with a knife.

Remember, alkali metals are always looking to lose their one valence electron to achieve a stable electron configuration!

Group VII Elements

Group VII elements are known as halogens. This group includes fluorine, chlorine, bromine, iodine, and astatine. Halogens have some distinct trends as well:

Oxidizing Power
Halogens are strong oxidizing agents, meaning they readily gain electrons. The oxidizing power, however, decreases as you move down the group.

Increasing Atomic Radius
Similar to Group I, the atomic radius of halogens increases down the group because additional electron shells are added.

Reactivity
Halogens are highly reactive, but unlike alkali metals, their reactivity decreases as you move down the group.

• They have seven electrons in their outer shell.
• They are one electron short of a full octet; hence, they readily gain an electron.
• Fluorine is the most reactive, while iodine is less so.

In summary, while Group I elements react by losing one electron, halogens react by gaining one electron to achieve a stable electron configuration.