Electron configurations PDF

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Electron Configurations

AP Chemistry – 6.7-6.9

When we add more electrons to the atom, the model becomes a little more complicated than the relatively simple hydrogen atom. For example, the subshells with a shell will having differing energy levels, where they increase with the angular momentum quantum number (l). In other words, the subshells for level n in order of increasing energy are ns < np < nd < nf. Orbitals within the same sublevel (e.g. 2px, 2py, 2pz) have the same energy and are said to be degenerate. When considering more than one electron, we will take another quantum number into consideration. Spin magnetic quantum number (ms) can have two possible values: +½ and –½ . When placing multiple electrons into orbitals, only two electrons may occupy the same orbital and they must have opposite spins. According to the Pauli Exclusion Principle no two electrons can have the same four quantum numbers. The electron configuration of an atom describes how the electrons are distributed among the atom’s orbitals. The ground state configuration is obtained by placing electrons in the lowest possible energy (the Aufbau Principle). When placing multiple electrons in degenerate orbitals, Hund’s Rule tells us the lowest energy configuration is the one that maximizes the number of electrons with the same spin. In other words, we must first fill each empty orbital with single electrons of matching spins before doubling up electrons in a single orbital. The periodic table is a useful guide for writing electron configurations.

We can write an electron configuration by starting in the upper left (at hydrogen) and then moving left to right, and top to bottom, until we arrive at the element in question. We will record all sublevels we go through as well as the number of electrons occupying each. We will follow the same procedure for writing condensed configurations, except rather than starting at hydrogen, we will begin with the noble gas that comes before the element in question. Groups of elements on the periodic table have similar electron configurations. For example, the halogens (group 7A or 17) all end in ns2 np5. Valence electrons are those found in the outermost shell and are involved in bonding. Core electrons are found in the full shells with n values less than the outermost shell.

Solved Examples 1) What is the maximum number of electrons in an atom that can have the following quantum numbers: n = 4, l = 1, ml = 1 Here we must remember that when l = 1, it is a p orbital and ml=1 represents one of those p orbitals. Each orbital can only hold two electrons, so there would be two possible electrons with these quantum numbers. They would only be different in their spin numbers (ms). 2) Consider the element phosphorus… a. How many valence electrons does it have? b. How many core electrons does it have? c. How many unpaired electrons does it have? We can answer these questions by first writing the electron configuration for phosphorus. [Ne] 3s2 3p3 Here we can see that the outermost level is n=3, and it contains 5 valence electrons. The core electrons are those represented by neon, which has 10 electrons. Finally, the 3p electrons should all be unpaired because there are three p orbitals, allowing them to each have their own orbital. 3) Write the condensed electron configurations for the following atoms. a. Ga

[Ar] 4s2 3d10 4p1

b. Ca

[Ar] 4s2

c. V

[Ar] 4s2 3d3

d. I

[Kr] 5s2 4d10 5p5

e. Pt

[Xe] 6s2 4f14 5d8

4) Identify the following elements based on their electron configurations. a. 1s2 2s2 2p4 2

2

6

2

7

By counting the superscripts we get the total number of electrons 1

b. 1s 2s 2p 3s

a=O

b = Na

c = Co

d = Tl

c. [Ar] 4s 3d

d. [Xe] 6s2 4f14 5d10 6p1 5) In which “block” of the periodic table would you find each of the following elements? a. Ni

Nickel is found in the d block, specifically the 3d sublevel

b. S

Sulfur is found in the p block, specifically the 3p sublevel

c. Ba

Barium is found in the s block, specifically the 6s sublevel

d. Pu

Plutonium is found in the f block, specifically the 5f sublevel

Name ________________________________

Period ______

ELECTRON CONFIGURATIONS

AP Chemistry – 6.7-6.9

Directions: Complete the following items related to the electron configurations. Show your work for all calculations. 1) The drawing to the right shows part of the orbital diagram for an element. a. As drawn, the drawing is incorrect. Why?

b. How would you correct the drawing without changing the numbers of electrons?

c. To which group in the periodic table does the element belong?

2) The average distance from the nucleus of a 3s electron in a chlorine atom is smaller than that for a 3p electron. In light of that fact, which orbital is higher in energy?

3) What is the maximum number of electrons that can occupy each of the following subshells? a. 3p

b. 5d

c. 2s

d. 4f

4) What is the maximum number of electrons in an atom that can have the following quantum numbers? a. n = 2, ms = -½

b. n = 5, l = 3

c. n = 4, l = 3, ml = -3

5) What are valence electrons? Core electrons?

6) Consider the element carbon in its ground state. a. How many valence electrons does it have?

b. How many core electrons does it have?

c. How many unpaired electrons does it have?

7) Write the condensed electron configurations for the following atoms, using the appropriate noblegas core abbreviations: a. Cs

b. Ni

c. Se

d. U

e. Pb

8) Identify the specific element that corresponds to each of the following electron configurations: a. 1s2 2s2 b. 1s2 2s2 2p4 c. [Ar] 4s1 3d5 d. [Kr] 5s2 4d10 5p4 e. 1s1

9) Identify the group of elements that corresponds to each of the following generalized electron configurations: a. [noble gas] ns2 np5 b. [noble gas] ns2 (n-1)d2 c. [noble gas] ns2 (n-1)d10 np1 d. [noble gas] ns2 (n-2)f6

10) What is wrong with the following electron configurations for atoms in their ground states? a. 1s2 2s2 3s1 b. [Ne] 2s2 2p3 c. [Ne] 3s2 3d5...