the modern periodic table

What is the periodic table?

A table that arranges all known elements in order of increasing atomic number, showing patterns in their properties.

What is the atomic number of an element?

The number of protons in the nucleus of an atom.

How are elements arranged in the modern periodic table?

By increasing atomic number.

What does the group number tell you?

The number of electrons in the outer shell of an atom.

What does the period number tell you?

The number of electron shells in an atom.

Why do elements in the same group have similar chemical properties?

Because they have the same number of electrons in their outer shell.

How many electrons do Group 1 elements have in their outer shell?

1 electron.

How many electrons do Group 7 elements have in their outer shell?

7 electrons.

How many electrons do Group 0 (noble gases) have in their outer shell?

8 electrons (except helium, which has 2).

Why does reactivity increase down Group 1?

Outer electron is further from the nucleus, so it is lost more easily.

What happens to reactivity in Group 7 (halogens) as you go down the group?

Reactivity decreases.

Why does reactivity decrease down Group 7?

Outer shell is further from the nucleus, so it is harder to gain an extra electron.

What happens to reactivity in Group 1 (alkali metals) as you go down the group?

Reactivity increases.

How can the periodic table help predict properties of elements?

By using patterns in groups and periods (reactivity, electron structure, etc.).

What is the electronic configuration of magnesium (atomic number 12)?

2,8,2.

Why is magnesium placed in Group 2?

Because it has 2 electrons in its outer shell.