Organic chemistry - PHAY0002

• Whats the atomic mass?


  The atomic mass is the total number of protons and neutrons including isotopes and this is usually the number at the bottom
• Whats the atomic number?


  This is the total number of protons in an atom
• how would you calculate the number of electrons?


  you would look at the atomic number as the total charge of an atom is neutral therefore the number of protons will equal the number of electons
• Whats an isotope?


  an isotope is an atom that has the same atomic number (so same number of protons) but has a different atomic mass (different neutrons)

  For instance, carbon has 6 protons and 6 neutrons but its isotope will have 6 protons but 7 neutrons
• Describe how electrons are positioned around the nucleus.

  The electrons are arranged in electron shells and each shell corresponds to its energy level.

  The shell closest to the nucleus is the first shell and has the lowest energy due to the strong attraction to the nucleus - cant move around much
• Describe what happens when the electrons are further away from the nucleus?


  As you move further away from the nucleus the electron shells are larger and higher in energy.
• how many electron shells are there per atom?

  there are 3 shells and within each shell there are orbitals which can only hold a maximum of 2 electrons.
• Whats the difference between an orbital and a electron shell?


  the electron shell is the general area where the electrons are found based on their energy, but within the shells are orbitals, which are a specific shape where there is a high probability of finding an electron.
• Describe the shape of the orbitals and how many orbitals and electrons are found within each shell?


  ·       The first shell contains only a single S orbital (1s) and therefore holds 2 electrons as each orbital can only contain 2 electrons

  ·       The second shell contains one 2s orbital and 3 2p orbitals therefore containing 8 electrons in the second shell

  ·       The third shell contains  one 3s orbital, three 3p orbitals and five 3d orbitals and therefore containing 18 electrons in the third shell

  S orbitals are spherical shaped

  P orbitals are dumbbell shaped

  
• why is it that orbitals can only contain 2 electrons?


  Because of the shape of the orbital the electrons can only spin in two opposite directions, electrons can't spin in the same direction
• Describe the shapes of each of the orbitals?


  The 1s orbital in the first shell is spherically shaped

  The 2s orbital in the second shell is also spherical, as its still quite close to the nucleus but a bit bigger

  The 2 p orbitals are dumbbell shaped but are at right angles to each other along the x-, y and z-axes = 2px, 2py and 2pz

  
• As hydrogen only has 1 electron which orbital would the electron occupy?

  The electrons will fill up the lowest energy orbitals first, as it won't be as stable in the higher energy shells and, therefore, will fill the lowest available energy orbital first.
• What's Hund's rule?


  Electrons fill orbitals of the same energy level one at a time before pairing up.

  For instance, in carbon, it will fill the first two shells, but when it gets to the P orbitals since there's 1 electron in the 2px orbital already then it can go in the next available orbital, it won't pair up with the electron in the 2px orbital until all the p orbitals contain at least one electron
• Write the electron configuration of oxygen in shorthand form. How many valence electrons does oxygen have?


  Oxygen's electron configuration: 1s2, 2s2 2p4 

  6 valence electrons
• Which electrons are available for bonding?

  Valence electrons - electrons in the outermost shells

  electrons in the 1s orbital are not considered as they're too close to the nucleus
• How do alkali metals become stable?

  ·  Alkali metals in group 1a will lose a single s electron from their valence shell to form a cation

  Example: sodium : sodium will lose 1 electron in its 3s orbital to have 8 valence electrons  and will become 1s2 2s2 2p6 to form a cation Na +
• How do halogens become more stable?

  halogens in group 7a will gain a p electron  to fill their valence shell
• How do elements in the middle of the periodic table achieve a noble gas configuration?

  Elements in the middle of the periodic table can't form ionic bonds because it’s too much energy to either gain or lose electrons to achieve a noble gas configuration.

  Therefore they share their electrons to form covalent bonds.
• How do atoms become more stable?

  They become more stable by having a full valence shell to achieve a noble gas configuration.

  8 electrons in valence shell = fully stable

  
• Lithium chloride is an ionic compound. Write the electron configuration of the lithium and chloride ions?

  • Li⁺ (Lithium ion): 1s²
  • Cl⁻ (Chloride ion): 1s² 2s² 2p⁶ 3s² 3p⁶
• Whats a covalent bond?


  A covalent bond is a bond that involves the sharing of a single pair of electrons between two atoms.
• How do two fluorine atoms interact?

  Two fluorine atoms each share one of their valence electrons with the other to obtain a closed-shell configuration through covalent bonds.

  The electron on the left fluorine atom will be attracted to the positively charged nucleus on the fluorine atom on the right vice versa

  In order for them to gain a noble gas configuration they each have to gain one electron

  Therefore there will be a sharing of 1 electron pair amongst the two atoms.

  
• Whats the difference between F2 and 2F?


  2F refers to the number of moles of fluorine so 2 moles

  F2 refers to the number of atoms so 2 atoms
• Draw the lewis structures of methanol (CH3OH)

  
• Draw the lewis structure of and methylamine (CH3NH2).

  
• How does electron sharing occur in terms of orbitals and give an example?

  A covalent bond forms when two atoms approach each other and a singly occupied orbital on one atom overlaps a singly occupied orbital on the other atom. The pair of electrons in the overlapping orbitals is now attracted to the nuclei of both atoms, holding the two nuclei together

  For instance: in hydrogen the two singly occupied 1s orbitals will overlap to form H2. The overlapping orbitals will form an elongated egg shape (elongated sphere).

  
• What is bond length?


  the distance that two nuclei can get close enough without repelling each other
• Why does the electron sharing process differ between H-H and C-H?


  As carbon has both S and P orbitals but hydrogen only has the s orbital
• Are all the bond lengths in methane CH4 the same, and why?


  Yes all C-H bonds are the same length, strength and angle as carbon forms 4 identical sp3 hybrid orbitals and therefore forms 4 identical bonds with the hydrogen atoms in methane.
• What is SP3 hybridisation?


  SP3 hybridisation occurs in all carbon atoms and this is where one 1 electron from the 2s orbital gets enough energy and gets promoted to the vacant p orbital.

  Then the 2s orbital and the three 2p orbitals combine and hybridise to form four sp3 orbitals which are identical.

  
• How are the orbitals arranged in an carbon atom?


  They form a tetrahedral shape and have a bond angle of 109.5.

  This is as they're are getting as far away from each other as possible, to minimise the repulsion between negatively-charged electrons, as all regions of the sp3 are negatively charged.

  
• Describe how a carbon atom bonds with a hydrogen atom (ch4)?


  Just like with hydrogen, each covalent bonds in methane forms when the 1 s electron orbital of a hydrogen atom overlaps with one of the sp3 electron orbitals of the carbon atom.
• What's a sigma bond?


  The strongest type of covalent bond that is cylindrically symmetrical and is formed between the overlapping of orbitals.

  
• What do dashed, wedged and straight lines represent?

  The dashed, wedge and straight lines are used to represent how the orbitals are arranged in 3d space but relative to the piece of paper.

  As the bonds in carbon point in different directions.

  The wedged bond will represent the bond coming out of the plane,

  The dashed bond represents the bond going towards the page.

  If a molecule has two carbons you would draw dashes and wedges for each carbon. The overall structure has to look like a tetrahedral.

  
• Define electronegativity?


  The ability of an atom to attract the electrons to itself in a covalent bond
• What atoms are electronegative and why?


  F,N,O & Cl

  These are because they are positioned on the right side of the periodic table thus attract electrons strongly and therefore have higher electronegativity.
• What is polarity and how does it arise?


  The uneven distribution of electrons due to the differences in electronegativities of the two atoms.

  For instance, in HF , fluorine attracts electrons to itself much more effectively than the hydrogen atom.

  The fluorine atom has a slight excess of electrons and is partially negatively charged.

  The hydrogen atom has a slight deficit of electrons and is partially positively charged.
• How would you differentiate between what atoms form ionic, covalent, polar bonds?

  If the electronegativities of the 2 atoms are at opposite ends of the scale (e.g. Na and F)forms an ionic bond.

  If the electronegativities are the same or only slightly different the atoms share the electrons equally and covalent bond is formed

  Bonds between C/H & N,O,F,CL are polar Covalent bonds

  Electronegativity increases from left to right across the periodic table and decreases from top to bottom.
• How would you determine whether a molecule as a whole is highly/weakly polar?


  high proportion of polar bonds = have high overall polarity,

  No polar bonds = non-polar

  Some polar bonds = low overall polarity
• How does the polarity of diphenhydramine affect its function?


  Diphenydramine is an older antihistamine that has a low polarity. In order to enter the brain the drug must cross the blood brain barrier which is composed of lipid molecules. Due to the low polarity its able to cross the membrane and can cause sedation.

  Cetirizine however is highly polar and therefore does not cause sedation as it cant penetrate the blood brain barrier.