# Strontium Valence Electrons

### Learning Objectives

1. Anaturally occurring amino acid with the formula c9h11no3 gives the following proton nmr spectrum when determined in deuterium oxide solvent with dcl added. The amino, carboxyl, and hydroxyl protons merge into a single peak at 5.1 ppm (4 h) in d2o. Determine the struc- ture of this amino acid and explain it.
2. Valence electrons - electrons in outermost shell, for Sr this is energy level 6 Strontium has 6 energy levels and 4 valence electrons. Note: If you are in a grade 12 class or later then you probably need to use the more complex (but correct) energy level model, but this is the simple Bohr model you use through most of high school: 2 electrons.
3. Strontium S Element 38 Mass Number: 88 Atomic weight: 87.62 g/mol Atomic number (Z): 38 Electrons: 38 Protons: 38 Neutrons: 50 Period: 5 Group: 2 Block: s.
4. Comprehensive information for the element Strontium - Sr is provided by this page including scores of properties, element names in many languages, most known nuclides and technical terms are linked to their definitions.

Determining Valence Electrons 1. Give the correct number of valence electrons for the element strontium, Sr, atomic #38. Which of the following electron dot notations is correct for the element calcium, Ca, atomic #20? Which of the noble gases does not have eight electrons in its outermost shell?

By the end of this section, you will be able to:

• Write Lewis symbols for neutral atoms and ions

## Lewis Symbols of Monoatomic Elements

In almost all cases, chemical bonds are formed by interactions of valence electrons in atoms. To facilitate our understanding of how valence electrons interact, a simple way of representing those valence electrons would be useful.

A Lewis electron dot diagram (or electron dot diagram or a Lewis diagram or a Lewis structure) is a representation of the valence electrons of an atom that uses dots around the symbol of the element. The number of dots equals the number of valence electrons in the atom. These dots are arranged to the right and left and above and below the symbol, with no more than two dots on a side. (It does not matter what order the positions are used.)

For example, the Lewis electron dot diagram for calcium is simply

Figure 1 shows the Lewis symbols for the elements of the third period of the periodic table.

Figure 1. Lewis symbols illustrating the number of valence electrons for each element in the third period of the periodic table.

Lewis symbols can also be used to illustrate the formation of cations from atoms, as shown here for sodium and calcium:Likewise, they can be used to show the formation of anions from atoms, as shown below for chlorine and sulfur:Figure 2 demonstrates the use of Lewis symbols to show the transfer of electrons during the formation of ionic compounds.

Figure 2. Cations are formed when atoms lose electrons, represented by fewer Lewis dots, whereas anions are formed by atoms gaining electrons. The total number of electrons does not change.

### Example 1: Writing Lewis DoT SYmbols of Elements

What is the Lewis electron dot diagram for each element?

1. aluminum
2. selenium
1. The valence electron configuration for aluminum is 3s23p1. So it would have three dots around the symbol for aluminum, two of them paired to represent the 3s electrons (or three single dots around the atom):

2. The valence electron configuration for selenium is 4s24p4. In the highest-numbered shell, the n = 4 shell, there are six electrons. Its electron dot diagram is as follows:

#### Check Your Learning

What is the Lewis electron dot diagram for each element?

1. phosphorus
2. argon

### Example 2: Writing Lewis DoT SYmbols of Ions

What is the Lewis electron dot diagram for each ion?

1. Ca2+
2. O2−
1. Having lost its two original valence electrons, the Lewis electron dot diagram is just Ca2+.

Ca2+

2. The O2− ion has gained two electrons in its valence shell, so its Lewis electron dot diagram is as follows:

#### Check Your Learning

The valence electron configuration of thallium, whose symbol is Tl, is 6s25d106p1. What is the Lewis electron dot diagram for the Tl+ ion?

### Key Takeaways

• Lewis electron dot diagrams use dots to represent valence electrons around an atomic symbol.
• Lewis electron dot diagrams for ions have fewer (for cations) or more (for anions) dots than the corresponding atom.

### Exercises

1. Explain why the first two dots in a Lewis electron dot diagram are drawn on the same side of the atomic symbol.

2. Is it necessary for the first dot around an atomic symbol to go on a particular side of the atomic symbol?

3. What column of the periodic table has Lewis electron dot diagrams with two electrons?

4. What column of the periodic table has Lewis electron dot diagrams that have six electrons in them?

5. Draw the Lewis electron dot diagram for each element.

a) strontium

b) silicon

6. Draw the Lewis electron dot diagram for each element.

a) krypton

b) sulfur

7. Draw the Lewis electron dot diagram for each element.

a) titanium

b) phosphorus

8. Draw the Lewis electron dot diagram for each element.

a) bromine

b) gallium

9. Draw the Lewis electron dot diagram for each ion.

a) Mg2+

b) S2−

10. Draw the Lewis electron dot diagram for each ion.

a) In+

b) Br

11. Draw the Lewis electron dot diagram for each ion.

a) Fe2+

b) N3−Movies about knives.

12. Draw the Lewis electron dot diagram for each ion.

a) H+

b) H

1. The first two electrons in a valence shell are s electrons, which are paired.

3. The second column of the periodic table

5.

a)

b)

7.

a)

b)

9.

a) Mg2+

b)

11.

a) Fe2+

b)

### One of the outermost electrons in a strontium atom in the ground state can be described by what sets of four quantum numbers?

#### Explanation:

Your starting point for this problem will be the electron configuration for a neutral strontium atom in its ground state, which looks like this

$' S r : ' 1 {s}^{2} 2 {s}^{2} 2 {p}^{6} 3 {s}^{2} 3 {p}^{6} 3 {d}^{10} 4 {s}^{2} 4 {p}^{6} \textcolor{red}{5} {s}^{2}$

As you can see, strontium's outermost electrons are located on the fifth energy level, in the 5s-orbital.

In order to completely describe these two electrons, you need to list the values of the four quantum numbers used to characterize their location and spin.

So, you know that the two electrons are located on the fifth energy level, which means that the principal quantum number, $n$, will be equal to $\textcolor{red}{5}$.

The angular momentum quantum number, $l$, which describes the subshell in which the electrons reside, will take the value specific for the s-subshell, i.e. $l$ will be equal to $0$.

For the s-subshell, the magnetic quantum number, ${m}_{l}$, can only take one possible value, and that is ${m}_{l} = 0$. Here ${m}_{l} = 0$ describes the s-orbital found in the s-subshell.

Finally, the spin quantum number, ${m}_{s}$, can take two possible values, ${m}_{2} = \pm \frac{1}{2}$.

### Strontium Ion Valence Electrons

Since two electrons occupy the 5s-orbital, one will have ${m}_{s} = \frac{1}{2}$, which describes spin-up, and the other ${m}_{s} = - \frac{1}{2}$, which describes spin-down.

Therefore, the quantum sets that describe the two outermost electrons electrons in a strontium atom will be

$n = 5 , l = 0 , {m}_{l} = 0 , {m}_{s} = + \frac{1}{2}$

and

### Ground State Electron Configuration Strontium

$n = 5 , l = 0 , {m}_{l} = 0 , {m}_{s} = - \frac{1}{2}$