1. a. The first number below the diagram represents the atomic radius.
b. The units for the atomic radius are picometers (pm).
c. The atomic radius is the distance from the center of an atom's nucleus to the outer edge of its electron cloud.
2. In general, the atomic radius increases as you go down a group. This is because each successive element in a group has an additional energy level (electron shell), which increases the distance between the nucleus and the outermost electrons. For example:
- Group 1: H < Li < Na < K
- Group 17: F < Cl < Br
3. As you move down a group, the number of energy levels (electron shells) increases. Each new energy level is farther from the nucleus, which increases the atomic radius. Although the number of protons in the nucleus also increases, the addition of new electron shells has a greater effect on the size of the atom than the increased nuclear charge.
4. In general, the atomic radius decreases as you go across a period from left to right. This is because the number of protons in the nucleus increases, leading to a stronger positive charge that pulls the electrons closer to the nucleus. The electrons are added to the same energy level, so there is no significant increase in shielding. For example:
- Period 2: Li > Be > B > C > N > O > F > Ne
- Period 3: Na > Mg > Al > Si > P > S > Cl > Ar
5. As you move across a period, the number of protons in the nucleus increases, which increases the nuclear charge. The electrons are added to the same energy level, so the shielding effect remains relatively constant. The increased nuclear charge pulls the electrons closer to the nucleus, resulting in a smaller atomic radius.
Parent Tip: Review the logic above to help your child master the concept of trends in the periodic table worksheet answers.
