1. Which of the following has the largest size? A. Cl B. Cl-, C. F, D. F-
QUESTION:
Which of the following has the largest size? A. Cl B. Cl-, C. F, D. F-
SCRIPT:
Which of the following has the largest size?
A chlorine atom… a chloride ion.. A fluorine atom… or a fluoride ion
PAUSE
Let’s look up these elements in the periodic table.
CLICK

2. decreasing SCRIPT, slide 2 Here’s chlorine CLICK and here’s fluorine
Both are members of the halogen family. They both belong to group seven A.
The trend in atomic size going up a group is decreasing.
Therefore, fluorine is smaller than chlorine.

3. Which of the following has the largest size? A. Cl B. Cl-, C. F, D. F-
QUESTION:
Which of the following has the largest size? A. Cl B. Cl-, C. F, D. F-
Cl vs. F: Cl is larger
Valence shell
is farther from
the nucleus
Cl vs. Cl-:
Cl: [Ne] 3s2 3p5
Cl-: [Ne] 3s2 3p6
[Ne]
SCRIPT:
Compared to fluorine, chlorine is a larger atom.
CROSS OUT choice C.
Since both have the same valence configuration, chlorine is larger than fluorine simply because the valence electrons of chlorine are in the third shell,
while those of fluorine are in the second shell. The third shell is farther away from the nucleus.
Let’s compare chlorine and chloride ion.
The electron configuration of chlorine is…. Neon core, 3s2, 3p5
It has seven valence electrons
HIGHLIGHT 3s2 3p5
Let’s try to visualize this….
Here’s the nucleus of chlorine…
CLICK Here’s the core, which has ten electrons…
CLICK and here’s the valence shell, with seven electrons
The electrons in valence shell will feel an inward pull from the nucleus…
CLICK
Remember that unlike charges attract. The nucleus is positive and electrons are negative.
But they won’t feel the full nuclear charge because the electrons in the core will exert an outward push
Electrons repel each other.
Each electron in the valence shell will also feel and repulsive force from other electrons in the valence shell
Now, let’s look at chloride ion. The electron configuration of chloride ion is… neon core, 3s2, 3p6.
HIGHLIGHT configuration
We have one extra electron in the valence shell.
HIGHLIGHT the 6 in 3p6
The nucleus is the same,… the core is the same… But the additional electron in the valence shell increases
Repulsion among electrons in the valence shell…. This makes the electrons spread out more…
Causing chloride ion to be larger than a chlorine atom.
This means, choice A ---chlorine--- is not the correct answer.
CROSS OUT choice A.
In general, when an atom gains electrons to form a negative ion, the ion formed is larger than the original atom.
Therefore, we can also say that choice C, fluorine, is smaller than fluoride.
So now, we just need to compare chloride and fluoride.
We can say that chloride is larger than fluoride for the same reason that chlorine is larger than fluorine.
They have the same valence configuration, but the valence shell of chloride ion is larger. The electrons are simply farther away from the nucleus.
CROSS OUT choice D.
The correct answer is B.
PAUSE
END RECORDING

4. Video ID: © 2008, Project VALUE (Video Assessment Library for Undergraduate Education), Department of Physical Sciences Nicholls State University Author: Glenn V. Lo Narrator: Funded by Louisiana Board of Regents Contract No. LA-DL-SELECT-13-07/08