Physical Chemistry Lecture 1 PDF

PHYSICAL CHEMISTRY Prof. Medhat Mostafa Abozid Faculty of Agriculture , Menoufia University At the end of 19 thcentury, the matter was distinct. Matter: anything had mass, position in space (can be specified) and consist of particles, At the end of19 thcentury, the energy was distinct. Ener...

PHYSICAL CHEMISTRY Prof. Medhat Mostafa Abozid Faculty of Agriculture , Menoufia University At the end of 19 thcentury, the matter was distinct. Matter: anything had mass, position in space (can be specified) and consist of particles, At the end of19 thcentury, the energy was distinct. Energy: in a form of light (electromagnetic radiation) was described as a wave massless and delocalized (their position in space couldn't be specified) In the 20th century discovered that: Light which has wave properties also shows matter properties (Dual nature of light) E = mc 2 E= energy, m= mass, c= the speed of light In the 20 th century discovered that: Matter has wave properties m= E/c 2 Therefore, it can be said that matter is restricted energy, and energy is liberated matter STRUCTURE OF MATTER DESCRIBE THE POSITION OF ELECTRON We need 4 quantum numbers to full describe the position of electron around the nuclei BOX AND ARROW CONFIGURATIONS Hund’s Rule: Each orbital will have one electron spinning in a common direction before two electrons will fill the same orbital. BOX AND ARROW CONFIGURATIONS Pauli’s Principle Only 2 electrons can occupy a given orbital. In full orbitals (orbitals containing 2 electrons of opposite spin) one electron must be spin up and the other spin down. The electrons are said to be paired. BOX AND ARROW CONFIGURATIONS The Aufbau Principle Electrons fill subshells of the lowest available energy , then they fill subshells of higher energy. BOX AND ARROW CONFIGURATIONS Rules for Filling Orbitals: 1- Lower-energy orbitals fill first (The Aufbau Principle). 2- An orbital can hold only 2 electrons with opposite spins (Pauli’s Principle). 3- If 2 or more degenerate orbitals available, 1 electron goes in each until all are half-full (Hund's Rule).  EXAMPLE Write the electronic configuration for an oxygen atom (O) by box and arrow configuration?  EXAMPLE Which atom would be expected to have a half-filled 4s subshell?  ELECTRON CONFIGURATION EXCEPTIONS Write the electronic configuration for chromium (Cr; atomic number 24) and copper (Cu; atomic number 29) by box and arrow configuration? ELECTRON CONFIGURATION EXCEPTIONS For instance, the ground state electron configuration of the transition metal chromium (Cr; atomic number 24) is [Ar]4s13d5 and that of copper (Cu; atomic number 29) is [Ar]4s13d10. In general, such exceptions involve subshells with very similar energy, and small effects can lead to changes in the order of filling. ELECTRON CONFIGURATION EXCEPTIONS In the case of Cr and Cu, we find that half- filled and completely filled subshells apparently represent conditions of preferred stability. This stability is such that an electron shifts from the 4s into the 3d orbital to gain the extra stability of a half-filled 3d subshell (in Cr) or a filled 3d subshell (in Cu).  PRACTICE Mark the following statement as (√) or (X), then correct the false: 1- Electrons fill subshells of the highest available energy , then they fill subshells of lower energy 2- An orbital can hold only 2 electrons with same spins 3- Principal quantum number describe the orbital shape  PRACTICE 1- Write the electronic configuration for iron (Fe; atomic number 26) and copper (Cu; atomic number 29) by box and arrow configuration? 2- Which atom would be expected to have a full-filled 4s subshell?  Lewis Structures 1) Find your element on the periodic table. 2) Determine the number of valence electrons. 3) This is how many electrons you will draw. Lewis Structures Find out which group (column) your element is in. This will tell you the number of valence electrons your element has. You will only draw the valence electrons. www.chem4kids.com Groups - Group 8 = 8 electrons Review Group 1 = 1 electron Except for He, it has Group 2 = 2 electrons 2 electrons Each column is called a “group” Each element in a group has the same number of electrons in their outer orbital, also known as “shells”. The electrons in the outer shell are called www.chem4kids.com “valence electrons” lewis structures' showing the valence electrons  Valence electrons for Elements Recall that the valence electrons for the elements can be determined based on the elements position on the periodic table. Lewis Dot Symbol  Valence electrons and number of bonds Number of bonds elements prefers depending on the number of valence electrons. In general - Fam ily # C o v a l e n t B o n d s* H a lo g e n s X 1 bond often F , B r , C l, I C a lc o g e n s O, S O 2 bond often N itr o g e n N, P N 3 bond often C a rb o n C , Si C 4 bond always Lewis Structures 1) Write the element symbol. 2) Carbon is in the 4th group, so it has 4 valence electrons. 3) Starting at the right, draw 4 electrons, or dots, counter-clockwise around the element symbol. Lewis Structures 1) Check your work. 2) Using your periodic table, check that Carbon is in the 4th group. 3) You should have 4 total electrons, or dots, drawn in for Carbon.  Lewis Structures On your worksheet, try these elements on your own: a) H b) P c) Ca d) Ar e) Cl f) Al What is Chemical bonding? Chemical bonds Force of attraction holding group(s) of atoms Na+ Cl- But why bonds are formed ?? Better stability against chemical reagents Octet rule Atoms noble gas configuration is more stable... He two electrons in the valence shell (1s2) + Na - Cl Cl 22 8 8 1 Very Ne reactive 22 88 78 Very Ar reactive  The Lewis Model of Chemical Bonding In 1916 G. N. Lewis proposed that atoms combine in order to achieve a more stable electron configuration. Maximum stability results when an atom is isoelectronic with a noble gas. An electron pair that is shared between two atoms constitutes a covalent bond.  Covalent Bonding in H2 Two hydrogen atoms, each with 1 electron, H..H can share those electrons in a covalent bond. H: H Sharing the electron pair gives each hydrogen an electron configuration analogous to helium.  Covalent Bonding in F2 Two fluorine atoms, each with 7 valence electrons,.... :..F.. F:.. can share those electrons in a covalent bond..... :.. F: F :.. Sharing the electron pair gives each fluorine an electron configuration analogous to neon.  The Octet Rule In forming compounds, atoms gain, lose, or share electrons to give a stable electron configuration characterized by 8 valence electrons..... :.. F: F :.. The octet rule is the most useful in cases involving covalent bonds to C, N, O, and F. Example Combine carbon (4 valence electrons) and four fluorines (7 valence electrons each).... C.. F. :.. to write a Lewis structure for CF4..... :..F:.. :..F: C : F.. :.. :..F: The octet rule is satisfied for carbon and each fluorine. Example It is common practice to represent a covalent bond by a line. We can rewrite.... :..F:.. :.. :..F :..F: C :..F:.. : F:.... as :.. F C F:.. :..F: