The element having chemical properties most similar to As is. The properties of the elements are determined by the arrangement of in their atoms.

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1 Group 17 (7A) Halogens - Colorful and corrosive nonmetals - Found in nature only in with other elements, such as with sodium in table salt (sodium chloride, NaCl) - All except At are as pure elements. - They exist in : i.e., F 2, Cl 2, Br 2, I 2-3 additional elements are diatomic: H 2, N 2, O 2 Group 18 (8A) Noble Gases - Colorless gases - Labeled the noble gases because of their of chemical reactivity. - Helium, neon, and argon don t combine with any other elements. Krypton and xenon combine with very few. - Previously known as gases. (Groups 3-12) Transition Metals & (no group number) Lanthanide/Actinides Series - Transition elements are common - Lanthanides and Actinides are not common The element having chemical properties most similar to As is. a. S b. Sb c. Se d. Si 2.6 Electronic Structure of Atoms The properties of the elements are determined by the arrangement of in their atoms. Ch 2 Page 13

2 This arrangement is understood using the quantum mechanical model developed by Erwin Schrödinger. (According to this theory), atoms are not completely free to move around the atom. Each electron is restricted to specific _ that are known as. The energy associated with each orbital is different The energy that electrons can have is (can only have discreet values) e.g., stairs quantized, a ramp is. Energy values available to electrons change only in. Electrons have both - like and - like properties. The behavior of electrons can be described using an equation called a wave function. The wave function also provide each electron with an address within an atom consisting of a. Shells, Subshells, and Orbitals Orbitals are grouped into shells and subshells. Shells Electrons are grouped in layers or shells around the nucleus. The farther out from the nucleus, - the the shell - the electrons it can hold, and - the the energy level of the electrons. - The first shell can hold electrons. - The second shell can hold electrons. - The third shell can hold electrons. Ch 2 Page 14

3 Shell Numbering (primary quantum number, ): Shells are numbered with integers starting with n=1. A shell can have as many subshells as the shell value. Subshells Subshells Numbering : Subshells are lettered in order s, p, d, f in order of energy. Therefore: - Shell n=1 has subshell (only an subshell) - Shell n=2 has subshells ( and subshells) - Shell n=3 has subshells (,, and subshells) - Shell n=4 has subshells (,, and subshells) subshell designation Orbitals Within each subshell, electrons are grouped into orbitals: regions of space within an atom where the specific electrons are to be found. s subshells can have orbital d subshells can have orbitals p subshells can have orbitals f subshells can have orbitals number of orbitals Each orbital can hold electrons of opposite spin. Ch 2 Page 15

4 Orbital Summary Problem: What is the maximum # of e - that can occupy the following subshells? Problem: What is the maximum # of electrons that can occupy the third shell? Problem: How many electrons are present in an atom in which the 1s, 2s, and 2p subsells are filled? Name the element. Orbital Shapes Orbitals are probability regions. They have shapes that include where the electrons are located 95% of the time. s orbitals are spheres. p orbitals are dumbbells. (usually lobes per orbital) (usually lobes per orbital) Ch 2 Page 16

5 The shapes of d orbitals f orbitals (usually lobes per orbital) and (usually lobes each) Electronic Configurations and the Periodic Table The exact arrangement of electrons in an atom s shells and subshells is the atom s electron configuration. It can be predicted by applying 3 rules. The 3 Principles for Order of Filling Energy Levels Rule 1: Always fill the energy levels first. (Aufbau Principle) - This is complicated by crossover of energies above the 3p sublevel. - The energy diagram can be used to predict the order of filling, but there are easier ways! Rule 2: Each orbital can hold a maximum of 2 electrons of spin. (Pauli Exclusion Principle) Rule 3: If you have orbitals of the same energy ( ), you fill 1 in each orbital before you double up. All unpaired e- all have the spin. (Hund s Rule) Ch 2 Page 17

6 The periodic table provides a method for remembering the order of orbital filling. It can be divided into blocks elements according to the last subshell filled. Atomic Electron Configurations An electron configuration is a summary of the orbital locations for all electrons in an atom. Electron configurations are described by writing the shell and subshell in order of increasing energy. The number of electrons occupying each subshell is indicated by a. A summary of the orbital location of each electron is written as, for example: Mg 1s 2 2s 2 2p 6 3s 2 etc. Shell # Subshell Type The number of electrons in the subshell A graphic representation can be made by indicating each orbital as a line or box and each electron as an arrow. The head of the arrow indicates the electron spin. Ch 2 Page 18

7 Problem: Determine the electron configuration and orbital box diagram for: H Li C V An alternate trick that can be used to determine the order or sublevel filling is: Problem: Determine the full electron configuration for the following elements. Also show the orbital diagram for each. Determine the number of unpaired electrons. Al V Ch 2 Page 19

8 Problem: Determine the noble gas shorthand electron configuration for the following: Se Sn Bi 2.9 Electron Dot Symbols Since electrons (those in the outer shell) are so important in the behavior of atoms, it is useful to be able to show them with the chemical symbol. Electron-dot symbol An atomic symbol with dots placed around it to indicate the number of valence electrons. These are cartoons and do not imply actual shapes. (Don t pair up until you get to the 5 th electron, except for He.) Gr 7A Valence Shell Electron Configuration Problem: Write the electron dot symbols for lead and Sr. Ch 2 Page 20