Unit Two: Elements & Matter February 1, 2016
Warm-Up: 2/1/2016 1. Fill in the following information: Atomic Symbol Ca 2+ Atomic Number Proton Neutron Electron 34 36 Mass Num. 2. Identify which family the following elements belong in: Chlorine Xenon Curium Barium 3. Solve the periodic pun: A prize element Atomic Mass
How can we communicate the location of an element on the periodic table?
The Location of Electrons Problem of defining nature of electrons in atoms solved by W. Heisenberg. Cannot simultaneously define the position and momentum (= m v) of an electron. We define e- energy exactly but accept limitation that we do not know exact position.
The Arrangement of Electrons Electrons in atoms are arranged as LEVELS (n) SUBLEVELS (l) ORBITALS (m l )
Energy Levels Each energy level has a number called the PRINCIPAL QUANTUM NUMBER, n Currently n can be 1 thru 7, because there are 7 periods on the periodic table
Energy Levels 6d 7s 5d 6s 4d 4p 5f 6p 4f 5p 5s 7s 6s 5s 6p 5p 6d 5d 4d 5f 4f 4s 3p 3d 4s 4p 3d Energy 3s 3s 3p 2p 2s 2p 2s 1s 1s
Types of Orbitals The most probable area to find these electrons takes on a shape So far, we have 4 shapes. They are named s, p, d, and f. No more than 2 e- assigned to an orbital
S-Orbital
P-Orbitals
D-Orbitals
F-Orbitals
Periodic Patterns 1 2 3 4 5 6 7 1s s 2s 3s 4s 5s 6s 7s d (n-1) 3d 4d 5d 6d p 2p 3p 4p 5p 6p 7p 1s f (n-2) 6 7 4f 5f
Electron Configuration A list of all the electrons in an atom (or ion) 2 electrons per orbital, maximum We need electron configurations so that we can determine the number of electrons in the outermost energy level. These are called valence electrons. The number of valence electrons determines how many and what this atom (or ion) can bond to in order to make a molecule
Maximum # of Electrons Maximum Number Electrons In Each Sublevel Maximum Number of Electrons In Each Sublevel Maximum Number Sublevel Number of Orbitals of Electrons s 1 2 p 3 6 d 5 10 f 7 14
Format for electron configuration 1s 1 row # shell # possibilities are 1-7 7 rows subshell possibilities are s, p, d, or f 4 subshells group # # valence e- possibilities are: s: 1 or 2 p: 1-6 d: 1-10 f: 1-14 Total e- should equal Atomic # What element has an electron configuration of 1s 1?
Rules for Electron Configuration Aufbau Principle: Electrons are added one at a time to the lowest energy orbitals available until all the electrons of the atom have been accounted for. Pauli Exclusion Principle: An orbital can hold a maximum of two electrons. To occupy the same orbital, two electrons must spin in opposite directions. Hund s Rule: Electrons occupy equal-energy orbitals so that a maximum number of unpaired electrons results.
Orbital Diagram Graphical representation of an electron configuration One arrow represents one electron Shows spin and which orbital within a sublevel
Notation Orbital Diagram 8 O 15.9994 O 8e - 1s 2s 2p Electron Configuration 1s 2 2s 2 2p 4 Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
Example Problems Write the electron configuration for the following elements Li N Ne K Zn Pb U
Shorthand Configuration A way of abbreviating long electron configurations Since we are only concerned about the outermost electrons, we can skip to places we know are completely full (noble gases), and then finish the configuration
Shorthand Configuration Step 1: Find the closest noble gas to the atom (or ion), WITHOUT GOING OVER the number of electrons in the atom (or ion). Write the noble gas in brackets [ ]. Step 2: Find where to resume by finding the next energy level. Step 3: Resume the configuration until it s finished.
Shorthand Configuration A B neon's electron configuration (1s 2 2s 2 2p 6 ) third energy level [Ne] 3s 1 C D one electron in the s orbital orbital shape Na = [1s 2 2s 2 2p 6 ] 3s 1 electron configuration
Shorthand Configuration Write the following in shorthand configuration: Ne K Zn Pb U
What about Ions? Electrons are lost or gained like they always are with ions negative ions have gained electrons, positive ions have lost electrons The electrons that are lost or gained should be added/removed from the highest energy level (not the highest orbital in energy!)
Common Charges 1 2 3 4 5 6 7
Example: Tin Tin Atom: [Kr] 5s 2 4d 10 5p 2 Sn +4 ion: [Kr] 4d 10 Sn +2 ion: [Kr] 5s 2 4d 10 Note that the electrons came out of the highest energy level, not the highest energy orbital!
Exceptions to the Rule Electron Configuration Exceptions Copper EXPECT: [Ar] 4s 2 3d 9 ACTUALLY: [Ar] 4s 1 3d 10 Copper gains stability with a full d-sublevel.
Why? s s 1 p 2 3 d 4 K 4s 1 Ca 4s 2 Sc 3d 1 Ti 3d 2 V 3d 3 Cr 3d 45 Mn 3d 5 Fe 3d 6 Co 3d 7 Ni 3d 8 Cu 3d 9 3d 10 Zn 3d 10 Ga 4p 1 Ge 4p 2 As 4p 3 Se 4p 4 Br 4p 5 Kr 4p 6 Energy n = 4 n = 3 n = 2 n = 1 4f 4d 4p 3d 4s 3p 3s 2p 2s 1s Cr 4s 1 3d 5 4s Cu 4s 1 3d 10 3d Cr 4s 1 3d 5 Cu 4s 1 3d 10
Valence Electrons Electrons are divided between core and valence electrons B = 1s 2 2s 2 2p 1 Core = [He], valence = 2s 2 2p 1 Br = [Ar] 3d 10 4s 2 4p 5 Core = [Ar] 3d 10, valence = 4s 2 4p 5
Valence Electrons & Octet Rule No. of valence electrons of a main group atom = Group number (for A groups) Atoms like to either empty or fill their outermost level. Since the outer level contains two s electrons and six p electrons (d & f are always in lower levels), the optimum number of electrons is eight. This is called the octet rule.