Fundamentals of Medicinal and Pharmaceutical Chemistry PDF

Fundamentals of Medicinal and Pharmaceutical Chemistry FUNCHEM.6 Ionic Bonding and the "electrolyte status" of body fluid D r. D a r r e n G r i ffi t h  General Chemistry - The...

Fundamentals of Medicinal and Pharmaceutical Chemistry FUNCHEM.6 Ionic Bonding and the "electrolyte status" of body fluid D r. D a r r e n G r i ffi t h  General Chemistry - The Essential Concepts by Chang Recommended and Goldsby 7e Reading  Section 9.1, 9.2, 9.4, 9.5 F U N C H E M. 6 I o n i c B o n d i n g a n d t h e " e l e c t r o l y t e s t a t u s " o f b o d y fl u i d 2 FUNCHEM.6 Learning outcomes Define ‘octet rule’ and recall ‘electronegativity’. Differentiate between ‘pure covalent’ and ‘polar covalent’ bonding. Explain ‘ionic bonding’ and ‘ionic character’. Predict whether a covalent, polar covalent or ionic bond will form based on a knowledge of electronegativity values. Explain the formation of ionic compounds using electronic configurations. Differentiate between ‘electrolytes’ and ‘non-electrolytes’ and recall principal electrolytes in body fluids. Solve calculations regarding electrolyte concentrations in mEq/L. Explain the importance of electrolytes in the body and consequences of electrolyte overload or deficiencies (e.g. hypo or hyperkalemia and hypo or hypernatremia). F U N C H E M. 6 I o n i c B o n d i n g a n d t h e " e l e c t r o l y t e s t a t u s " o f b o d y fl u i d 3 Noble gas configuration Noble gases are chemically stable (chemically inert). They share a common e- configuration of 8 valence electrons that is very stable. He is an exception with 2 e-. 4  Octet Rule An atom other than hydrogen tends to form bonds until it is surrounded by eight valence electrons  Atoms are most stable if they have a filled or empty outer shell of electrons.  Except for H and He, a filled outer shell contains 8 valence e-.  Atoms will: gain or lose electrons (ionic) share electrons (covalent) to achieve a noble gas configuration. 5 Chemical bonds Ionic bond  An ionic bond is the electrostatic force that holds the cations and anions in an ionic compound.  Atoms either completely lose one or more e- to become positive cations or gain one or more e- to become negative anions. Watch the animation titled ‘Ionic vs Covalent Bonding’ on the VLE 6 Chemical bonds Covalent  A covalent bond is formed when atoms share one pair of electrons  Neither atom is willing to give up e- or is strong enough to take e- away. Watch the animation titled ‘Ionic vs Covalent Bonding’ on the VLE 7 Ionic vs Covalent How do you know whether an ionic or covalent bond will form? Knowing the electronegativity of individual atoms can help determine the type of interaction between atoms Electronegativity values can be used to distinguish between covalent, polar covalent and ionic bonds Electronegativity is the ability of an atom to attract toward itself the electrons in a chemical bond. – Recall from FUNCHEM.3 8 Electronegativity The ability of an atom in a molecule to attract towards itself electrons in a chemical bond Electronegativity the same, electrons shared equally.  H 2, N 2, O2. One atom more electronegative than the other, e- not equally shared.  H-F, H-Cl. δ+ H – F δ- H–H Non-polar Polar 9 Electronegativity trends Pauling scale of relative electronegativity values 10 Types of chemical bonds Atoms of elements with widely different electronegativity values tend to form ionic bonds.  Ionic - difference in electronegativity > 2.0  Polar covalent - difference in electronegativity 0.3 - 2.0 The most electronegative elements are the nonmetals  Pure covalent - difference in (Groups 5A–7A) and the least electronegativity = 0. electronegative elements are the alkali and alkaline earth metals (Groups 1A–2A) – Ionic bonds 11 Types of chemical bonds Pure covalent – H2 and F2 E.N. [H] = 2.1 E.N. [H] = 2.1 E.N. [F] = 4.0 E.N. [F] = 4.0 ∆E.N. = 2.1 – 2.1 = 0 ∆E.N. = 4.0 – 4.0 = 0 Pure covalent bond Pure covalent bond 12 Types of chemical bonds Polar covalent – H2O δ- O – H δ+ E.N. [O] = 3.5 E.N. [H] = 2.1 ∆E.N. = 3.5 – 2.1 = 1.4 Polar covalent bond 13 Ionic and ionic charcter 1s22s1 1s22s22p5 1s2 1s22s22p6 E.N. [Li] = 1.0 E.N. [F] = 4.0 ∆E.N. = 4.0 – 1.0 = 3 The greater the difference in Ionic bond electronegativity, the greater the ‘ionic character’ 14 Some salt for practice NaCl E.N. [Na] = 0.9 E.N. [Cl] = 3.0 ΔE.N. = 2.1 11 Na : 1s22s22p6 3s1 17 Cl : 1s22s22p63s23p5 Removal of this e- gives a Requires an e- to give a very very stable configuration stable configuration [Na]+ : 1s22s22p6 [Cl]- : 1s22s22p63s23p6 A 3s electron from a sodium atom is transferred completely to a 3p orbital of a chlorine atom. 15 Calcium and oxygen Ca – O E.N. [Ca] = 1.00 E.N. [O] = 3.5 ΔE.N. = 2.5 20 Ca : 1s22s22p6 3s23p6 4s2 8 O : 1s22s22p4 Removal of 2 e- gives a very Requires 2 e- to give a very stable configuration (noble stable configuration gas) [Ca]2+ : 1s22s22p6 3s23p6 [O]2- : 1s22s22p6 Two 4s electrons from a calcium atom are transferred completely to a 2p orbitals of the oxygen atom. 16 Properties of ionic compounds Ionic interactions take place between metal and non-metal atoms. Can form lattice structures held together by electrostatic interactions. Have high melting points. Generally soluble in water. 17 Electrolytes - ions in solution An electrolyte is a substance that, when dissolved in water, results in a solution that can conduct electricity (separate into charged particles). Both weak electrolytes (separate partially) and strong electrolytes (separate fully) exist Nonelectrolytes do not conduct electricity when dissolved in water (do not form charged particles). Ions are hydrated in aqueous solution. This is the process by which ions are surrounded by water molecules in a specific manner (Displayed to the right). When ions move their hydration spheres move with them Electrolytes perform many important regulatory roles in our bodies by virtue of their charged properties. 18 Water – Dipole Hydrogen  E.N. = 2.1 Oxygen δ-  E.N. = 3.5 Creation of a dipole moment. Area of partial negative charge & area of δ+ partial positive charge. δ+ 19 Electrolytes in the body Cell Blood  K+, Mg2+, Na+.  Na+, K+, Ca+, Mg+.  HPO42-, proteins, SO42-,  Cl-, HCO3-, proteins, organic HCO3-, Cl-. acids, HPO4-, SO42-. Interstitial fluid  Na+, K+, Ca2+, Mg2+  Cl-, HCO3-, organic acids, HPO4-, SO42-. 20 Equivalents can be used to represent an amount of a charged substance An equivalent of any substance is an amount of material that will give or react with an Avogadro's number of electrical charges Weight Eq = Atomic or Molecular Weight/ n where n is the charge Examples Na Na+ + e- 23g 6 x 1023 electrons An equivalent of Na+ is 23g Ca Ca2+ + 2 e- 40g 2 moles of electrons An equivalent of Ca2+ is 20g Equivalents = (mass x valence) molar mass 21 In clinical situations Electrolyte status of the blood plasma or serum is measured. Results represented in different ways. In healthcare the most common representation of electrolytes is milliequivalents per litre  mEq/L How many mEq in 1 Eq? 1000 mEq in 1 Eq 22 Importance of electrolytes Changes in the concentrations of sodium and potassium in blood can lead to serious medical emergencies Useful terms related to electrolyte disorders  -emia “in the blood”  -hypo a condition of low concentration  -hyper a condition of high concentration  -natr represents sodium (Latin –natrium)  -kal represents potassium (Latin –kalium) 23 Nervous system and electrolytes K+ and Na+ move in and out of channels in the membrane of nerve cell walls (some channels only permit K+ to pass through)  Net result – electrical signal Deficiencies in these ions can lead to serious problems  Hypokalemia can lead to cardiac arrest. A diet low in K+ can lead to hypokalemia You can read this short review to gain an insight into the importance of K+ ions in cardiac function and health. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3016067/pdf/ecc1 5e096.pdf 24 LoSalt – essential and deadly KCl  40% more potassium in our bodies than sodium.  Potassium is found in all parts of the body.  Red blood cells have most, followed by muscles & brain tissue.  It is the main cationic electrolyte found inside cells. 25 Deadly KCl If too much potassium outside the nerve cells, the potassium inside cannot escape and electrical impulse dies away. Potassium overdose paralyses the central nervous system, causes convulsions, diarrhoea, kidney failure and heart attack. In some countries condemned prisoners who agree to donate their organs for transplants may be executed by being given a ‘non-toxic’ lethal injection of potassium chloride. 26 Learning outcomes Define ‘octet rule’ and recall ‘electronegativity’. Recall and differentiate between ‘pure covalent’ and ‘polar covalent’ bonding. Explain ‘ionic bonding’ and ‘ionic character’. Predict whether a covalent, polar covalent or ionic bond will form based on a knowledge of electronegativity values. Explain the formation of ionic compounds using electronic configurations. Differentiate between ‘electrolytes’ and ‘non-electrolytes’ and recall principal electrolytes in body fluids. Calculate electrolyte concentrations in mEq/L. Explain the importance of electrolytes in the body and consequences of electrolyte overload or deficiencies (e.g. hypo or hyperkalemia and hypo or hypernatremia). 27 Thank you F O R M O R E I N F O R M AT I O N P L E A S E C O N TA N T D r. D a r r e n G r i ffi t h E M A I L : d g r i ffi t h @ R C S I. C O M 28