Lecture 3 Chemistry P2 Bonds MCQ PDF

Fundamentals of Chemistry: Part 2 Bonds 4BICH001W Biochemistry Dr Sarah K Coleman Learning Outcomes Name key types of atomic bonding Briefly describe key types of atomic bonding relevant to organic molecules Relate the Octet Rule to chemical bonds Understa...

Fundamentals of Chemistry: Part 2 Bonds 4BICH001W Biochemistry Dr Sarah K Coleman Learning Outcomes Name key types of atomic bonding Briefly describe key types of atomic bonding relevant to organic molecules Relate the Octet Rule to chemical bonds Understand what is meant by a Lewis Structure Be able to draw basic Lewis structures Pauling Scale Across a PERIOD electronegativity increases Greater number of protons = greater attraction for electrons Electronegativity Decreasing electronegativity down a GROUP Atoms have more electron shells, so have a bigger radius. Electronegativity and Polarity Ability of an atom to attract electrons toward itself in a chemical bond Electronegativity of an atom is related to its ionisation energy (losing an electron) and electron affinity (gaining an electron) Electronegativity can be used to estimate if a given bond will be; non-polar covalent, polar covalent or ionic  Types of Bonds Ionic Bond Covalent Bond Metallic Bond Between a metal and non- Between two non- Between atoms in a metal atom metals atoms metal e.g. Sodium chloride, NaCl e.g. water, H2O e.g. copper, Cu  Ionic and Covalent Bonds Previous lecture: The OCTET RULE The Octet Rule describes? a) How elements aim to become more stable by having eight outer electrons b) How music becomes harmonious c) How arachnids descended from insects d) How to pluralise octopus Any questions: You can type in the chat function box during this live session (synchronous)? Or onto the Question Board in the Biochemistry Blackboard module and I will look at them later (asynchronous). Ionic and Covalent Bonds Ionic Bond Covalent Bond Atoms form OCTETS To become more stable By losing, gaining or sharing valence electrons By formation of ionic bonds or covalent bonds M is a metal; Nm is a non-metal Remember electrons are negatively charged, e- Ionic Bonding Metals tend to LOSE electrons so become POSITIVE CATIONS (+ve charge) Non-metals tend to GAIN electrons so become NEGATIVE ANIONS (-ve charge) Atoms are NEUTRAL but IONS are CHARGED particles Ionic Bonding: elements want full octet Formation of Ions Any questions: You can type in the chat function box during this live session (synchronous)? Or onto the Question Board in the Biochemistry Blackboard module and I will look at them later (asynchronous). Ionic and Covalent Bonds Ionic Bond Covalent Bond Atoms form OCTETS To become more stable By losing, gaining or sharing valence electrons By formation of ionic bonds or covalent bonds M is a metal; Nm is a non-metal Remember electrons are negatively charged, e-  Covalent Bonds Non-metals react together and SHARE electrons to achieve the complete outer shell octet Electrons are SHARED Both atoms now have full outer shell This is the COVALENT bond. A strong binding force  Each Chlorine atom has 7 valence electrons The electrons are shared to achieve a full octet The bonding electron pair is circled (the middle electron pair) This is a single bonding pair Forms a single bond Single bonds are shown as a single dash line (arrow)  Each oxygen atom has 2 unpaired electrons Has a valence shell of 6 electrons Both oxygen atoms want to gain 2 electrons So, both electron pairs are shared Shared electron pairs are bonding pairs Other electron pairs are lone pairs Two bonding pairs of electrons (circled) These form a double bond A double bond is shown as 2 dashes More complex multiple bonding: part 1 Triple bonds: the sharing of 3 pairs of electrons e.g. ethyne C2H2 (also known as acetylene) Carbon has 4 valence electrons Hydrogen has one valence electron Wants full octet (8 electrons) Wants full 1s orbital (2 electrons) In TOTAL only 10 electrons available Can you draw out the Lewis Dot structure indicating the bonding electron pairs? ETHYNE Structure, C2H2 The carbon-carbon pair shares 6 electrons; a triple bond The carbon-hydrogen pairs share 2 electrons; a single bond All atoms now have a complete outer valence shell Any questions: You can type in the chat function box during this live session (synchronous)? Or onto the Question Board in the Biochemistry Blackboard module and I will look at them later (asynchronous). More complex multiple bonding: part 2 Resonance binding or delocalised electrons e.g. ozone, O3 Oxygen atom is: Normal molecular oxygen is: or Ozone structure can be represented by: or However, experimental studies have shown that the two bonds present are identical! Resonance binding or delocalised electrons e.g. ozone, O3 Theory states that one pair of bonding electrons is spread over the entire region of the molecule. Dotted line indicates delocalised electrons Termed delocalised bonding These show the possible electron structure of the molecule with delocalised electrons They are termed Resonance formulae of the molecule  Why a particular Lewis Structure? Some molecules could theoretically have different Lewis Structures, e.g. CO2 Atoms and molecules will always favour the lowest energy level How can we calculate the preferred (correct) structure? The FORMAL CHARGE is calculated DEFINITION of FORMAL CHARGE: difference between the number of valence electrons in the free atom and the number of electrons assigned to that atom in a Lewis structure. DEFINITION of FORMAL CHARGE: difference between the number of valence electrons in the free atom and the number of electrons assigned to that atom in a Lewis structure. Formal Charge = (No. of electrons in valence shell of free atom) – (No. of bonds to atom) – (No. of unshared electrons in atom) Want this number to be as low as possible! CO2 EXAMPLE: Number of electrons in valence 6 4 6 4 6 6 shell of free atom minus Number of bonds -2 -4 -2 -2 -4 -2 minus Number of unshared -4 -0 -4 -4 -0 -4 electrons Formal Charge is: 0 0 0 -2 +2 0 CO2 EXAMPLE: Formal Charge is: 0 0 0 -2 +2 0 The SUM of the Formal Charge should be EQUAL to charge of the molecule (so zero for neutral molecules) Lower numbers for Formal Charge (so 0 0 is better than +2 -2 ) Negative Formal charges on electronegative atoms. If alternate Lewis structures are possible the BEST one will: Have no formal charge Have minimum Formal charge possible Negative Formal charges on MOST electronegative atoms  Breaking the Octet Rule Second period elements cannot have more than 8 electrons Third period elements can have more they have d orbitals that can be used for bonding Some elements (though ones not so important for biochemistry) Some molecules with an odd number of valance electrons will break Octet Rule e.g. nitric oxide commonly have less than 8 electrons e.g. Be, Beryllium Al, Aluminium B, Boron Summary slide: The difference between ionic and covalent bonds and what atoms they are likely to occur with Why knowing the atomic number and electron configuration helps to predict types of bonds and the structure of a molecule Be able to represent simple molecular structures via Lewis structures Organisms, their molecules and chemistry get more complicated! Any questions: You can type in the chat function box during this live session (synchronous)? Or onto the Question Board in the Biochemistry Blackboard module and I will look at them later (asynchronous). MCQ quiz for Lecture 3: Fundamentals of Chemistry part 2 Answers will be given in your Seminar sessions – with further discussion. You must attempt before your seminar session. These quizzes are part of your learning for the Biochemistry module They will aid your on-going studies at the University of Westminster Q1) Atoms come together to form molecules. Molecules join to form larger structures. What are the key types of atomic bonding? a) Peptide, glycosidic and covalent. b) Covalent, iconic and metallic. c) Ionic, metallic and carbon. d) Hydrogen, covalent and ionic. e) Metallic, ionic and covalent. Q2) Ionic bonds are usually found in _____and mean that the atoms _______ electrons. a) Metals (e.g. within gold); transfer or accept. b) Salts (between metals and non-metals); transfer or accept. c) Non-metallic compounds (e.g. carbon and carbon); share. d) Salts (between metals and non-metals); share. e) Non-metallic compounds (e.g. carbon and carbon); transfer or accept. Q3) If a molecule is described as polar, this means? a) The molecule is only found at either the north or south polar regions b) The atom has lost an electron. c) The molecule has an unequal distribution of electrons. d) The compound is in its ionic form. e) The molecule has an equal distribution of electrons. Q4) The image shows the structure of? The lines indicate covalent bonds. How many shared electrons are indicated by the single line and how many by the double line? a) Ethanol; 1 electrons (one bonding pair); 2 electron (2 bonding pairs). b) Ethanol; 2 electrons (one bonding pair); 4 electron (2 bonding pairs). c) Ethanoic acid; 1 electrons (one bonding pair); 2 electron (2 bonding pairs). d) Ethanoic acid; 2 electrons (one bonding pair); 4 electron (2 bonding pairs). e) Methanoic acid; 2 electrons (one bonding pair); 4 electron (2 bonding pairs). Q5) The atomic number of hydrogen is one, for carbon six and for oxygen eight. Which image shows the correct Lewis Dot structure for water? a) H=O=H d) b) e) O-H-H c) H=O=H