Question

1. collect data: beginning with na, record the number of energy levels, number of protons, and atomic radius for each element in period 3.

element na mg al si p s cl ar
number of energy levels
number of protons
atomic radius (pm)

1. observe: what happens to the radius as you move across a period?
2. explore: investigate other periods in the periodic table. does the same trend occur?

does the same trend occur?
hypothesize why this trend occurs.

1. analyze: consider how the number of protons might affect the size of the electron cloud.

a. as you move across a period, are new energy levels added?
b. what happens to the number of protons in the nucleus as you move from one element to the next across a period?
c. if the proton number increases while the number of energy levels remains constant, what happens to the attractive force

Explanation:

Step1: Recall periodic - table properties

Elements in the same period have the same number of energy levels.

Step2: Analyze trends across a period

As we move across period 3 from Na to Ar:

• The number of energy levels for all elements in period 3 is 3.
• The number of protons for Na is 11, Mg is 12, Al is 13, Si is 14, P is 15, S is 16, Cl is 17, and Ar is 18.
• The atomic radius of Na is approximately 186 pm, Mg is 160 pm, Al is 143 pm, Si is 118 pm, P is 110 pm, S is 103 pm, Cl is 99 pm, and Ar is 97 pm. As we move across a period, the atomic radius decreases. This is because the number of protons increases (nuclear charge increases), while the number of energy levels remains the same. The increased nuclear charge pulls the electrons closer to the nucleus, reducing the atomic radius.
• For other periods in the periodic table, the same trend occurs. The increased nuclear charge with a constant number of energy levels causes the atomic radius to decrease across a period.
• Regarding the effect of protons on the electron - cloud:
• A. As you move across a period, new energy levels are not added.
• B. The number of protons in the nucleus increases by 1 as you move from one element to the next across a period.
• C. If the proton number increases while the number of energy levels remains constant, the attractive force between the nucleus and the electrons increases.

Answer:

Element	Na	Mg	Al	Si	P	S	Cl	Ar
Number of protons	11	12	13	14	15	16	17	18
Atomic radius (pm)	186	160	143	118	110	103	99	97

1. The atomic radius decreases as you move across a period.
2. Yes, the same trend occurs. Hypothesis: The increased nuclear charge (more protons) with a constant number of energy levels pulls the electrons closer to the nucleus, reducing the atomic radius.
3. A. No.

B. The number of protons increases by 1.
C. The attractive force between the nucleus and the electrons increases.