Question

q2 chemistry: u3l2 effective nuclear charge
prepwork part 2: atomic radius
directions: read the passage below. as you read, annotate the important information and vocabulary words. then answer the questions.
**part 1: read & annotate:
periodic trend: atomic radius
atomic radius is a measure of the size of an atom, usually from the nucleus to the outermost electron. the trend in atomic radius across the periodic table can be explained by two main factors: effective nuclear charge (zeff) and energy levels, both of which relate directly to the electrostatic forces described by coulombs law.
across a period (left to right):
as you move from left to right across a period, the number of protons in the nucleus increases. this leads to an increase in zeff, which is the effective nuclear charge felt by valence electrons. although electrons are being added, they go into the same energy level, and the amount of shielding from inner electrons remains relatively unchanged. according to coulombs law, the electrostatic attraction between the positively charged nucleus and negatively charged electrons becomes stronger as the number of protons increases. this stronger attraction pulls the electrons closer, resulting in a smaller atomic radius. therefore, atomic radius decreases across a period.
down a group (top to bottom):
as you move down a group, new electron shells (energy levels) are added. even though the number of protons also increases, the increase in distance from the nucleus causes a decrease in the electrostatic force according to coulombs law. additionally, increased shielding by inner electrons further reduces the attraction between the nucleus and valence electrons. the result is a weaker pull on the outermost electrons, and atoms become larger. so, atomic radius increases down a group.
part 2: multiple choice questions

1. **what causes atomic radius to decrease across a period?

a. more neutrons
b. more shielding
c. increased zeff
d. added energy levels

1. **why does atomic radius increase down a group?

a. decreased proton count
b. more shielding and energy levels
c. lower zeff
d. loss of electrons

1. *which atom has the smallest atomic radius?

a. li
b. b
c. f
d. na

1. which atom is the largest?

a. mg
b. ca
c. sr
d. ba
part 3: true or false

1. atomic radius increases across a period. ____
2. **more protons mean a stronger pull on electrons. ____
3. the atom gets larger when more energy levels are added. ____
4. *atomic radius decreases from na to cl. ____
5. ** all elements in the same period have the same number of energy levels. ____

be uncommon. change history.
page 8
bohr model:
coulombic force of attraction
how nucleus attracts electrons
the bromine
of net electrons
force of +7. this
takes into account
nuclear charge of br(35e
shielding - repulsive force
valence shell (28)

Explanation:

Step1: Answer question 1

The passage states that as you move left - to - right across a period, the number of protons increases, leading to an increase in \(Z_{eff}\), and this causes the atomic radius to decrease.

Step2: Answer question 2

When moving down a group, new energy levels are added, and there is more shielding by inner electrons. This is in line with option B.

Step3: Answer question 3

Fluorine (\(F\)) is on the far right of its period among the given options (\(Li\), \(B\), \(F\), \(Na\)). Since atomic radius decreases across a period, \(F\) has the smallest atomic radius.

Step4: Answer question 4

Among \(Mg\), \(Ca\), \(Sr\), and \(Ba\), \(Ba\) is the lowest in its group. As atomic radius increases down a group, \(Ba\) is the largest.

Step5: Answer question 5

The passage clearly says that atomic radius decreases across a period. So the statement “Atomic radius increases across a period” is False.

Step6: Answer question 6

According to Coulomb's Law, more protons (more positive charge) mean a stronger electrostatic attraction (pull) on electrons. So the statement “More protons mean a stronger pull on electrons” is True.

Step7: Answer question 7

When more energy levels are added (moving down a group), the atomic radius increases (the atom gets larger). So the statement “The atom gets larger when more energy levels are added” is True.

Step8: Answer question 8

\(Na\) and \(Cl\) are in the same period. Since atomic radius decreases across a period, atomic radius decreases from \(Na\) to \(Cl\). So the statement “Atomic radius decreases from \(Na\) to \(Cl\)” is True.

Step9: Answer question 9

Elements in the same period have the same number of energy levels (electron shells). So the statement “All elements in the same period have the same number of energy levels” is True.

Answer:

1. C. Increased \(Z_{eff}\)
2. B. More shielding and energy levels
3. C. \(F\)
4. D. \(Ba\)
5. False
6. True
7. True
8. True
9. True