Periods and Atomic Size (8.2.1)

Question 1

• Atomic radii increase with increasing electron shielding.

Answer 1

• Atomic radii increase with increasing electron shielding.

Question 2

• Atomic radii decrease with increasing effective nuclear charge.

Answer 2

• Atomic radii decrease with increasing effective nuclear charge.

Question 3

• Cations have smaller radii than their neutral atoms.

Answer 3

• Cations have smaller radii than their neutral atoms.

Question 4

• Anions have larger radii than their neutral atoms.

Answer 4

• Anions have larger radii than their neutral atoms.

Question 5

For main block elements:
Atomic size increases moving down a column.
Atomic size decreases moving from left to right
across a period.

Moving down:
More electron shielding leads to larger size.
Moving across:
Higher effective nuclear charge pulls the
electrons closer.

Answer 5

For main block elements:
Atomic size increases moving down a column.
Atomic size decreases moving from left to right
across a period.

Moving down:
More electron shielding leads to larger size.
Moving across:
Higher effective nuclear charge pulls the
electrons closer.

Question 6

With a higher effective nuclear charge and less electron
shielding, the cation has a smaller radius than the
neutral atom.

With a lower effective nuclear charge and more electron
shielding, the anion has a larger radius than the neutral
atom.

Answer 6

With a higher effective nuclear charge and less electron
shielding, the cation has a smaller radius than the
neutral atom.

With a lower effective nuclear charge and more electron
shielding, the anion has a larger radius than the neutral
atom.

Question 7

What happens to the size of an atom when it loses an electron?

Answer 7

The atom becomes smaller. (A)

Question 8

Which of the following phenomena illustrates the difficulty in calculating the size of an atom?

Answer 8

Heisenberg uncertainty principle. (A)

Question 9

How does the size of the cation compare to its corresponding atom?

Answer 9

The cation is smaller. (A)

Cations are formed when an atom loses one or more electrons and takes on a positive charge. Losing an electron causes the nucleus to pull harder on the remaining electrons. This causes a decrease in size. Therefore, the cation is smaller than its corresponding atom.

Question 10

Which of the following is the periodic trend for size of an atom?

Answer 10

The correct answer is B:

Increasing from right to left and from up to down.

Explanation:
As you move down a group, the size of the atoms increases because each atom has a larger nucleus and more electrons. As you move across the periodic table from left to right, the nuclear charge increases causing the electrons to move in closer to the nucleus, which causes the size of the atom to decrease.

Question 11

For a given element, how does the size of the anion compare to the size of the atom?

Answer 11

The anion is larger. (B)

An atom becomes an anion by gaining one or more electrons. When an atom gains an electron, it becomes larger because the attractive forces from the nucleus are distributed among more electrons. The result is that the ion expands.

Question 12

What is the maximum number of electrons that may be found in a 3p energy sublevel?

Answer 12

6. (C)

Question 13

Why is it difficult to measure the size of an atom?

Answer 13

The outer edge of an atom is difficult to determine. (D)

Determining exactly where the outer edge of an atom is presents scientists with the greatest problems. The outer edge is usually defined by a boundary where all the electrons are inside of 90%, 95%, or 99% of the time.

Question 14

Why do groups on the periodic table have similar chemical properties?

Answer 14

All members of the group have similar electron configurations. (D)

Question 15

Within a period, what happens to the size of an atom as the atomic mass increases?

Answer 15

The atom gets smaller (D).

Within a period, as the atomic mass increases, the size of the atom decreases. The increase in atomic mass increases the atomic force the nucleus exerts on the electrons. The increased atomic forces pull the electrons in and reduces the size of the atom.

Question 16

Which of the following represents the orbital configuration for oxygen at its ground state?

Answer 16

(C).

This diagram correctly shows the electrons in the orbital filling diagram for oxygen. Note that in the p energy sublevel, there are two electrons in one of the orbitals and one each in the other two orbitals. According to Hund’s Rule, the electrons must singly fill all the orbitals before they double up.