Valence Electrons: PDF

Valence Electrons What is a Valence Electron? The electrons that are in the highest (outermost) energy level. That level is also called the valence shell Of the atom. Electrons not in the outermost shell are called core electrons. Bohr Atomic Structures Electron Co...

Valence Electrons What is a Valence Electron? The electrons that are in the highest (outermost) energy level. That level is also called the valence shell Of the atom. Electrons not in the outermost shell are called core electrons. Bohr Atomic Structures Electron Configuration of Na: 1s22s22p63s1 The first energy level contains 2 electrons. (s orbital…1s2) The second level contains 8 electrons. (2s and 2p orbitals…2s22p6) How many electrons do you see in the outermost level? 3s1… 1electron! This is the Valence number. Sodium has 1 Valence Electrons How many valence electrons are in the following atoms? Ne O Na Cl  How many valence electrons are in the following atoms? 1s22s22p6 1s22s22p63s23p64s23d104p4 [Kr]5s24d105p2 [Ne]3s23p3  Valence electron trends 1) As you go down a group the number of electrons in the valence shell stays the same 2) As you go across a period (left to right) the # of e- in the valence shell of the main group elements increases one by one - This ignores the transition metals Notice the e- trends in the Groups and Periods Lewis dot Structures for the atoms of groups 1-2 and 13-18 of The periodic table The Main group elements 9 The number of valence electrons in an atom determines: The properties of the atom The way that atom will bond chemically As a rule, the fewer electrons in the valence shell, the more reactive the element is. When an atom has eight electrons in the valence shell, it is stable.  Noble Gas Stability Noble gases are usually unreactive This is because they have full valence shells An element with a full valence shell is a happy element  For two atoms to join together atoms must gain, lose or share electrons Elements with full valence shells do not easily gain or lose electrons  Noble Gas Stability Atoms want to gain stability Atoms will try to gain or lose electrons to have a full valence shell Metals try to lose electrons Non-Metals try to gain electrons Electron Dot Structure Electron-dot structure consists of the element’s symbol representing the nucleus, surrounded by dots representing the element’s valence electrons. Lewis Theory Gilbert N. Lewis (1875-1946) recognized valence (outmost) electrons fundamental to bonding electron transfer resulting in ionic bonds sharing electrons resulting in covalent bonds atoms tend to acquire a noble-gas electronic  Lewis Dot Structure Lewis wrote in a memorandu m dated March 28, 1902 Basic Chemical Bonding  Lewis Structures Lewis structures show ONLY valence electrons. Examples: Sodium (Na) is in group 1A, so we know it has 1 valence electron. Group 1A is known as the alkali metals Beryllium (Be) is in group 2A, so we know it has 2 valence electrons. Group 2A is known as the alkaline earth metals  Lewis Structures Lewis structures for oxygen Oxygen is in group 6A, so it has 6 valence electrons. How to Draw Lewis Structures 1) Look at the element you want to draw the structure for and see what group it is in. 2) Draw dots around the symbol according to how many valence electrons it has. Example: Draw a Lewis Structure for calcium 1) We see calcium (Ca) is in group 2A, so it has 2 valence electrons 2) Ca