11.4 Electron Configurations And the Periodic Table

11.4 Electron Configurations (p377) The electron configuration of hydrogen is “1s1” This means there is one electron in the 1s orbital.

11.4 Electron Configurations Rule 1: Electrons occupy the lowest orbital energies first. 2p Energy 2s Then here 1s First here

11.4 Electron Configurations Rule 2: Pauli Exclusion Principle: Two electrons can occupy the same orbital. They have different “spins” 2p Energy 2s 1s One Two

11.4 Electron Configurations Rule 3: Electrons will not “pair up” in the same orbital until all energy levels are occupied. 2p Energy 2s 1s

Example: Sodium (Na) Start by drawing a dashed line for each sub-orbital needed in the correct order. 1s 2s 2px 2py 3s 2pz

11.4 Electron Configurations Look at your field diagram The order of the “seats” is the same as the order of orbitals. Notice the 4th energy level has seats closer than some of the 3rd energy level. Which orbital fills up first, 4s or 3d? Yes, 3d.

Electron Configuration Quicker way to write the orbital notation Example: sodium Becomes 1s22s22p63s1 1s 2s 2px 2py 3s 2pz

11.4 Electron Configurations Examples: Li (Z=3), N (7), O(8) (See book) Mg can be written as [Ne]3s2 Valence electrons are the electrons in the highest principal energy level of an atom. They are involved in bonding with other atoms. Nitrogen has electrons in n = 1 and 2. Level 2 is the valence level. 1s22s22p3 Nitrogen has 5 valence electrons.

11.4 Electron Configurations The core electrons are the inner electrons, and are not involved in bonding. Question: What elements have the same number of valence electrons as N? Where are they on the periodic table? Elements with the same number of valence electrons have similar chemical properties.

Number one less than row number Number two less than row number B. Electron Configurations and the Periodic Table. Helium actually part of s-block 1 2 s-block 3 p-block d-block Number one less than row number 4 5 6 7 f-block Number two less than row number

Example: Germanium (Ge) Do the orbital notation 1s 2s 2p 2p 2p 3s 3p 3p 3p 4s 3d 3d 3d 3d 3d 4p 4p 4p

11.4 C. Atomic Properties and the Periodic Table Representative Elements - groups 1A-8A Ionization – ionization is when an atom loses an electron. Remember: ______________ lose electrons. _______________ gain electrons. Going down a group, atoms are more likely to lose an electron. Cs is more likely to lose an electron than Li. Metals Nonmetals

11.4 C. Atomic Properties and the Periodic Table Atomic size – decreases going up and right. Decreases going up because electrons are closer at lower principal energy levels. Decreases going right because the + charge in the nucleus is stronger.

Atomic Size Size generally decreases Size generally decreases

11.4 C. Atomic Properties and the Periodic Table Ionization energy - the energy required to remove an electron from an atom in the gas phase. increases up a group increases to the right

Ionization Energy Increases increases

Checkpoint Which element has a larger atomic size? Sulfur or chlorine? Answer: Sulfur Which element has the larger ionization energy? Sodium or potassium? Answer: Sodium http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/atomic4.swf http://video.google.com/videoplay?docid=-2134266654801392897