1279 words - 6 pages

Worksheet 11 - Electronic Structure of Atoms

The Schroedinger equation defines wave equations which describe the

distribution of electrons around the nucleus. The wave functions that satisfy the

Schroedinger equation are called atomic orbitals. They define the allowed

energy states of the electrons.

The energy levels are described by three quantum numbers, n, l and ml.

n is the principal quantum number and has values of 1, 2, 3, ...

The value of n determines the size of the orbital and the energy of electrons in

that orbital.

l is the angular momentum quantum number as has values of 0 through n -1.

The value of l determines the shape of the orbital.

ml is the magnetic quantum number and has values of -l through +l and

determines the orientation of the orbital.

1. Complete the first two columns of the chart shown below for n = 1

through n = 4.

n l ml orbital name # e- total e- in level n

1 0 0 1s 2

2 0 2

1 -1, 0, 1 6

3 0

3d

4

The l = 0 orbitals are called s orbitals. The l = 1 orbitals are called p orbitals.

For l = 2, 3 and 4, they are called d, f and g orbitals. Each orbital can contain a

maximum of 2 electrons.

2. Fill in the orbital names and the number of electrons per orbital

and per energy level in the chart.

3. How many orbitals are present in each of the principal levels?

n = 1 n = 2 n = 3 n = 4 n = 5

The s orbitals are spherical. They increase in size with increasing values of n.

The p orbitals are dumbbell shaped. Each of the three p orbitals is oriented

differently in space, as shown below.

Again, size of these orbitals increases with n.

The shapes of the d and f orbitals are more complex and are shown in the

textbook.

4. Which of the following orbitals can not exist?

1s 3p 1p 7d 3f 4s 2d 8g

5. Name the orbitals described by the following quantum numbers

(e.g. n = 2, l = 1 would be 2p)

n = 3, l = 0 n = 3, l = 2 n = 3, l = 3 n = 5, l = 0 n = 3, l = 1

6. How many orbitals in an atom can have the designation:

5p 3s n=4 4d n=3

1s 2s 3s

px py pz

The importance of these orbitals is apparent when we look at the Periodic

Table. Period 1 (H and He) is the n = 1 energy level. This means that there is

only one orbital (1s) available. H has 1 electron and He has 2, completely filling

the 1s orbital. Electrons in the same orbital must have different spin states ( a

4th quantum number), either spin up (↑) or spin down (↓).

So, the electron configuration for H is 1s1 and He is 1s2, since each s orbital can

hold two electrons.

These can also be drawn out as:

H 1s __ and He 1s __

In He, the electrons are paired, one spin up and one down. Parallel spins are

not allowed in an orbital. Electron spin is the 4th quantum number, ms, with

values of +½ and -½ .

The next element is Li with 3 electrons or 1s2 2s1

The 2s orbital is higher in energy than the 1s orbital

Li 2s __

1s __

7. The next element is ______ with ...

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