Define isoelectronic series. Put the K+, Ca2+, Cl-, and Ar ions and atoms in order of increasing size and explain the trends.
Count the number of electrons for each atom
Then, explain the (column) size trend for Mg2+ versus Ca2+ ions
Is the order cl k ca Ar? How would you count electrons? What would the size trend be?
Ah, isoelectronic series, a fancy term for a group of atoms or ions that have the same number of electrons. It's like dressing up a bunch of clowns in the same outfit. Now, let's sort our circus animals here.
First up is K+, the potassium ion. Since it has a positive charge, it lost an electron, so it has 18 electrons.
Next is Ca2+, the calcium ion. The 2+ means it lost two electrons, leaving it with 18 electrons as well.
Then we have Cl-, the chloride ion. With a negative charge, it gained an electron, giving it a total of 18 electrons.
Lastly, we have Ar, which is argon, an atom rather than an ion. It has 18 electrons too, just like the other clowns in this series.
Now, let's organize them by size. From smallest to largest, it would be K+, Cl-, Ca2+, and Ar. The trend is that the size increases as we go from right to left, or from positive ions to negative ions to atoms.
As for the size trend between Mg2+ and Ca2+ ions, Mg2+ is actually smaller than Ca2+. This is because Ca2+ has two more protons in its nucleus, which pulls the electrons in closer and makes the ion smaller. It's like squeezing a balloon filled with clowns, but with protons and electrons instead.
An isoelectronic series refers to a set of ions or atoms that have the same number of electrons. In this case, we have K+, Ca2+, Cl-, and Ar.
To determine the order of increasing size, we need to consider the atomic number and the charge of the ions.
The number of electrons for each atom is as follows:
- K+: This ion is formed by removing one electron from a neutral potassium atom (K). Therefore, it has 18 electrons.
- Ca2+: This ion is formed by removing two electrons from a neutral calcium atom (Ca). Therefore, it has 18 electrons.
- Cl-: This ion is formed by gaining one electron by a neutral chlorine atom (Cl). Therefore, it has 18 electrons.
- Ar: This is a neutral atom of argon, and it has 18 electrons.
To determine the order of increasing size, we need to consider the effective nuclear charge experienced by the electrons. The effective nuclear charge refers to the attraction the electrons feel towards the nucleus of an atom. The greater the effective nuclear charge, the more tightly the electrons are drawn towards the nucleus, resulting in a smaller atomic size.
In this case, comparing K+ and Cl-, they both have 18 electrons, but K+ has a greater effective nuclear charge due to its higher atomic number. As a result, the K+ ion will be smaller than Cl-.
Next, comparing Ca2+ and Ar, they also both have 18 electrons. However, Ar has a greater effective nuclear charge compared to Ca2+ because of its higher atomic number. Therefore, Ar will be smaller than Ca2+.
So the order of increasing size is:
- Cl- < K+ < Ca2+ < Ar
The general trend is that as you move from left to right across a period (horizontal row) on the periodic table, the effective nuclear charge increases, leading to a decrease in atomic size. Additionally, as you move down a group (vertical column), the number of electron shells increases, resulting in an increase in atomic size.
An isoelectronic series refers to a group of atoms or ions that have the same number of electrons. In other words, they possess identical electronic configurations. To determine the size trend and order of K+, Ca2+, Cl-, and Ar ions and atoms, we need to consider the number of electrons in each species.
First, let's count the number of electrons for each atom:
K+: To determine the number of electrons for K+, we need to consider its atomic number. Potassium (K) has an atomic number of 19, which means it has 19 protons and, in a neutral atom, 19 electrons. However, K+ has a positive charge due to the loss of one electron, so it has 18 electrons.
Ca2+: Calcium (Ca) has an atomic number of 20, meaning it has 20 protons and, in a neutral atom, 20 electrons. Ca2+ has a positive charge because it loses two electrons, leaving it with 18 electrons.
Cl-: Chlorine (Cl) has an atomic number of 17, which means it has 17 protons and, in a neutral atom, 17 electrons. However, Cl- has a negative charge due to gaining one electron, resulting in a total of 18 electrons.
Ar: Argon (Ar) has an atomic number of 18, meaning it has 18 protons and, in a neutral atom, 18 electrons.
Now that we have determined the number of electrons for each atom/ion, let's put them in order of increasing size:
Increasing size: Cl-, K+, Ca2+, Ar
The general trend for size follows this pattern: as you move down a group (column) in the periodic table, the size of atoms and ions increases. This trend is due to the addition of extra energy levels or shells, which results in an increased atomic radius. However, within a group, when comparing ions, the size decreases as the positive charge increases. This occurs because the increased positive charge attracts and pulls the negatively charged electrons closer to the nucleus, leading to a smaller ionic radius.
In the case of Mg2+ versus Ca2+ ions, both ions have the same number of electrons (18), but calcium (Ca2+) is larger. This is because calcium, being in the third period of the periodic table, has one additional energy level or shell compared to magnesium (Mg2+), which is in the second period. The added energy level in Ca2+ causes an increase in size despite both ions having the same number of electrons.
I looked up the neutral atom and ionic species and this is what I found from smallest to largest. It isn't what I expected.
Ar < Cl^- < Ca^2+ < K^+
I thought in an isoelectronic series (which this is since all atoms/ions have 18 electrons) that Cl^- would be larger than Ar because you are adding an extra electron to make the -1 ion, the electrons repel each other, and that makes the size larger. On that basis then, Ar, the next element after Cl will be slightly smaller because there is an extra + charge in the nucleus (18 vs 17) and that pulls the outside electrons in a little more. So far so good. That makes sense and is true. Ar is slightly smaller than Cl^-. Then my reasoning goes that the K^+ should be slightly smaller than Ar because the same number of electrons are there and there is one more proton in the nucleus. That should pull the electrons in more and the trend to Ca^2+ should continue BUT that doesn't fit the data.
That is the trend for O^2-, F^-, Ne, Na^+, Mg^2+. I don't know why it isn't the trend in your series.
Here is a site showing the trend in decreasing size for an isoelectronic group. Scroll down part way to see the diagram. http://chemwiki.ucdavis.edu/Inorganic_Chemistry/Descriptive_Chemistry/Periodic_Trends_of_Elemental_Properties/Periodic_Trends_in_Ionic_Radii
Here is the site where I picked up the atom/ion sizes. Scroll to almost the bottom of the page.
http://www.angelo.edu/faculty/kboudrea/periodic/trends_atomicradius.htm