He 3. What is the Heisenberg Uncertainty Principle? __ 4. The behavior of an atom is determined mostly by the number of __ it contains, specifically the number of __ __ electrons it has. This is why elements in the same __ of the periodic table are most similar. 5. When moving ACROSS a period on the periodic table, atomic radius __ and ionization energy 6. When moving DOWN a column on the periodic table, atomic radius __ and ionization energy __ This is because the atom is gaining more __ , which means there is a __ attraction for electrons. 7. Elements in group 1 and group 17 are highly reactive because they only need to gain or lose __ electron in order to complete the __ (8 valence electrons)

## Step 1<br />The Heisenberg Uncertainty Principle is a fundamental concept in quantum mechanics. It states that it is impossible to know both the exact position and momentum of a particle at the same time. This principle is a result of the wave-particle duality of matter, which is a fundamental concept in quantum mechanics.<br /><br />## Step 2<br />The behavior of an atom is determined mostly by the number of protons it contains, specifically the number of electrons it has. This is why elements in the same group of the periodic table are most similar.<br /><br />## Step 3<br />When moving across a period on the periodic table, the atomic radius decreases and ionization energy increases. This is because as you move across a period, the number of protons increases, which increases the positive charge of the nucleus and pulls the electrons closer to the nucleus, decreasing the atomic radius.<br /><br />## Step 4<br />When moving down a group on the periodic table, the atomic radius increases and ionization energy decreases. This is because as you move down a group, the number of electron shells increases, which increases the distance between the nucleus and the outermost electrons, increasing the atomic radius.<br /><br />## Step 5<br />Elements in group 1 and group 17 are highly reactive because they only need to gain or lose one electron in order to complete the octet (8 valence electrons). Group 1 elements have one electron in their outermost shell and can easily lose it to achieve a stable electron configuration. Group 17 elements have seven electrons in their outermost shell and can easily gain one electron to achieve a stable electron configuration.