Tuesday Do Now:
Which of the following has a LARGER atomic radius:
1)
2)
3)
4)
5)
Sulfur, Oxygen, Technetium
Aluminum, Phosphorus, Argon
Boron, Gallium, Indium
Carbon, Fluorine, Oxygen
Neon, Xenon, Krypton
Let’s see a review (6 min) – Note – This has to be done through finding the video via Google
search.
http://education-portal.com/academy/lesson/atomic-and-ionic-radii-trends-among-groups-andperiods-of-the-periodic-table.html#lesson
Introduce ion, cation, and anion definitions
Ion – an atom or group of atoms that have a positive or negative charge.
Atom – NEUTRAL: electrons balance out protons
Ions form when electrons are transferred between atoms. Why do atoms want to transfer
electrons? Atoms try to have a complete valence shell.
An ion with a positive charge is a cation.
An ion with a negative charge is an anion.
A trick you can use to remember is think of a cat. Cats are cute, everybody (ok most people)
love cats. Cats are lovable and positive. Cations are positively charged ions.
Let’s look at lithium. What’s the easiest way to have a complete valence shell for lithium? By
losing one electron.
So what happens to lithium when it loses an electron? Before losing an electron, it had 3 p and 3
e, thus the charge was 0 (neutral). Now, when lithium lost an electron it still has 3p but only 2e,
so it’s charge is? +1
Work through sodium: 11p 11e -> 11p 10e = +1
Label your periodic table with a +1 over group 1A.
Work through beryllium: What’s easiest way to a complete valence shell? Lose 2 electrons:
4p 4e -> 4p 2e = +2
Work through Calcium:
20p 20e -> 20p 18e = +2
Label your periodic table with a +2 over group 2A
Skip over the transition metals. For group 3A, what’s the shortest path for boron to get a
complete valence shell? How many electrons does it need to gain? How many does it need to
lose?
Easier to lose 3 than gain 5. Label your table with a +3 over group 3A.
What about group 4A? They would need to lose 4 or gain 4, which is hard either way, so we
skip over group 4A.
Group 5A, what does nitrogen need? Gain 3 or lose 5. Gain 3:
Nitrogen = 7p 7e -> 7p 10e = -3
Phosphorus = 15p 15e -> 15p 18e = -3
Place a -3 over group 5A
Group 6A, what does oxygen need? Gain 2 electrons or lose 6, so oxygen prefers to gain 2
electrons:
Oxygen: 8p 8e -> 8p 10e = -2
Label group 6A with a -2 charge
Group 7A – fluorine can either gain 1 electron or lose 7! Fluorine prefers to gain 1 electron:
Fluorine: 9p 9e -> 9p 10e = -1 charge
Label group 7A with a -1 charge.
What about group 8A? They don’t need to change, they already have a completed valence shell!
They don’t want to gain or lose ANY electrons!
Practice Problems:
Predict the ionic charge for the following atoms when they form ions:
1)
2)
3)
4)
5)
6)
Gallium
Iodine
Neon
Potassium
Magnesium
Bismuth
Trends in ionic size:
Li -> Li+ Neutral to having more protons than electrons! Size gets smaller. There’s overall a net
+ charge, holding all of the electrons very close.
What happens to the size of a cation as you go across a period? The same thing as when you go
across a period for atomic radius, which is??
What happens to the size of a cation as you go down a group? The same thing as when you go
across a period for atomic radius, which is??
F -> F- neutral atom to having more negative chagres than positive ones. The ion has trouble
controlling all of the negative charges, letting them spread out more. Thus the size gets bigger.
What happens to the size of an anion as you go across a period? The same thing as when you go
across a period for atomic radius, which is??
What happens to the size of an anion as you go down a group? The same thing as when you go
across a period for atomic radius, which is??
Draw a periodic Table:
Label arrows across a period and down a group explaining what happens for each of the
following:
Shielding (increase, decrease, stays the same)
Effective Nuclear Charge (increases, decreases, stays the same)
Atomic Size (increases, decreases, stays the same)
Ionic Size (increases, decreases, stays the same)