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The modern periodic table organizes elements based on their atomic number.

There are 18 vertical columns, which are called groups.
There are 7 horizontal rows, which are called periods.

There are $\boxed{18 \text{ groups}}$ and $\boxed{7 \text{ periods}}$ in the modern periodic table.

Question 3: An element has atomic number 17.

*a) To which group and period does it belong?

*b) Is it a metal or a non-metal?

*c) What type of ion will it form?

a) To which group and period does it belong?

The electronic configuration is $2, 8, 7$.

Since there are 3 electron shells (K, L, M), the element belongs to Period 3.

Since there are 7 valence electrons, the element belongs to Group 17.

The element belongs to $\boxed{\text{Group 17}}$ and $\boxed{\text{Period 3}}$.

b) Is it a metal or a non-metal?

Elements with 5, 6, or 7 valence electrons are typically non-metals.

With 7 valence electrons, the element is a non-metal.

The element is a $\boxed{\text{non-metal}}$.

c) What type of ion will it form?

To achieve a stable octet, an element with 7 valence electrons will gain 1 electron.

Gaining an electron results in a negative charge. Therefore, it will form a uninegative ion.

The element will form a $\boxed{\text{uninegative ion}}$ (e.g., $\text{Cl}^{-}$).