In the early 1800s, scientists ordered elements by their physical and

properties and their

In

Dmitri

arranged the elements by their

but switched the order if their

were

to those in a different

were left to ensure this worked.

The

number is how many electrons are in the

Elements in the same group have

Each new

represents another

The transition metals are good

and are very

they have a

surface and can have more than one

They also make good

As you move

group 1, there is

reactivity, and decreasing

They are

reactive down the group because the attraction between the

and the electrons is

as the shells are

Alkali metals are in group

They are all

and very

and have a

Alkali metals react violently with

to produce hydrogen and a

Alkali metals react violently with

when heated, to produce

Alkali metals react with

to produce a

As you move down group 7, the elements become

reactive, and they have

melting and boiling points.

Elements in group 7 are called the

and they all exist in

Elements in group 7 form

when they are bonded covalently and form -1 ions called

when they form

A displacement reaction can occur between a

halogen and the

of a

one.