Activity Electron Configurations

Transcription

1 Activity Electron Configurations Directions: This GLA worksheet goes over two different ways to write the electron configuration for a specific element. Electron configurations are a way of specifying where the electrons of an element reside within its electron cloud. In other words, it is like writing the addresses of the electrons of a specific element. Part A introduces determining the number of electrons in a neutral element. Part B discusses writing the complete electron configuration for specific elements. Part C discusses writing the electron configuration for ions. The worksheet is accompanied by instructional videos. See for additional materials. Part A Counting Electrons for a Neutral Element The first step in writing the electron configuration of a specific element is to determine the total number of electrons that the element has. The total number of electrons in a neutral element is equal to the total number of protons. Recall that the number of protons for any element is equal to its atomic number, and can be found on the periodic table. For each of the following neutral elements, determine the total number of electrons. a) Mg 12 total electrons b) Fe 26 total electrons Example #1: a) Ag total electrons b) Cl total electrons c) Ca total electrons Part B Writing Electron Configurations Within an atom, electrons reside in orbitals that are located at specific, fixed distances away from the nucleus. These orbitals are specified by both a number and a letter. The number, called the principle quantum number (n = 1, 2, 3, ), specifies the principle shell. The principle shells that are closest to the nucleus (smaller n value) are at a lower energy than those further from the nucleus (larger n value). Within each principle shell, there are subshells (specified by the letters s, p, d and f) that indicate specific areas where the probability of finding an electron is greatest. Activity Page 1 of 4

2 Writing electron configurations can be thought of as filling the electron cloud, beginning with the lowest energy orbital first. The order in which the orbitals should be filled can be determined using the diagram below. Starting at 1s, the red arrows and dotted lines follow the order of filling. For example, as the diagram demonstrates, the 3d subshell begins filling only after the 4s has been filled. Orbitals and subshells can also be partially filled if the element does not have enough electrons to completely fill it. The maximum amount of electrons you can place in a specific subshell depends on the shape of the subshell (represented by the letters s, p, d, or f). Once a subshell is full (contains the maximum number of electrons), the next subshell then begins filling. The maximum number of electrons that can be placed in a specific subshell is shown below: Maximum Subshell Number of Electrons s 2 p 6 d 10 f 14 The number of electrons that are contained within a specific subshell are represented as a numerical superscript. For example, the electron configuration for lithium (Li), which has 3 total electrons, is 1s 2 2s 1. This shows that 2 electrons exist in the 1s subshell and 1 electron exists in the 2s subshell. Write the complete electron configuration for each of the following elements: a) Si 1s 2 2s 2 2p 6 3s 2 3p 2 b) Co 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 7 Example #2: a) Na b) Mn Activity Page 2 of 4

3 Electron configurations can also be written in the shorthand noble gas form, which is especially useful for larger atoms that have many electrons. If we take a look at the electron configuration for sodium (Na), for example, it contains the electron configuration of the noble gas neon (Ne), plus one additional electron. We can put this noble gas in brackets and then write the rest of the electron configuration next to it, as shown below: Write the shorthand noble gas electron configuration for each of the following elements: a) Br [Ar] 4s 2 3d 10 4p 5 b) Ir [Xe] 6s 2 4f 14 5d 7 Example #3: a) Te b) Ba c) Po Part C Writing Electron Configurations for Ions Ions form when a neutral atom gains or loses electrons. The charge of an ion is given by: CChaaaaaaaa = pppppppppppppp eeeeeeeeeeeeeeeeee Metal atoms will lose electrons, and the number of electrons lost is equal to the positive charge. For example, a Li + ion started with 3 electrons (as determined from the atomic number), and lost one electron (because it has a +1 charge), so has 2 remaining electrons. The electron configuration for Li + is 1s 2. Write the electron configuration for each of the following ions: a) Ca 2+ 1s 2 2s 2 2p 6 3s 2 3p 6 b) N 3-1s 2 2s 2 2p 6 Example #4: a) Br - b) Pb 2+ Activity Page 3 of 4

4 Part D Extra Practice Write both the complete and shorthand noble gas electron configurations for each of the following elements or ions: a) Be b) S c) K d) I e) Se 2- f) Sn 2+ g) Ba 2+ Activity Page 4 of 4

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