Front

Vertical columns on the periodic table are called ___?

Back

Groups (or Families)

Front

Periods on the periodic table are __________.

Back

Horizontal Rows

Front

Who developed the first periodic table in 1869?

Back

Dmitri Mendeleev

Front

What is the name of the element with the symbol 'Na'?

Back

Sodium

Front

Groups on the periodic table are __________.

Back

Vertical Columns

Front

What does the atomic number represent in the periodic table?

Back

The number of protons in an atom's nucleus.

Front

What is the significance of the periodic table's arrangement?

Back

It shows the periodic trends and properties of elements.

Front

What are the horizontal rows in the periodic table called?

Back

Periods

Front

What is the name of the element with atomic number 12?

Back

Magnesium

Front

What is the main organizing principle of the modern periodic table?

Back

Atomic number.