Investigation

How did Mendeleev arrange elements?

By increasing atomic mass, grouping elements with similar properties.

What did Moseley change about the periodic table?

He arranged elements by increasing atomic number.

What is the Periodic Law?

Properties repeat periodically when elements are arranged by atomic number.

What happens to atomic radius across a period?

It decreases from left to right.

What happens to atomic radius down a group?

It increases because atoms gain energy levels.

What is ionization energy?

The energy required to remove a valence electron.

What happens to ionization energy across a period?

It increases from left to right.

What happens to ionization energy down a group?

It decreases because valence electrons are farther from the nucleus.

What is electronegativity?

An atom's ability to attract electrons when forming a compound.

What is the shielding effect?

Inner electrons shield valence electrons from the nucleus's attraction.