Molecule Concept and Chemical Bonds PDF

MOLECULE CONCEPT and CHEMICAL BONDS Dr. Göksemin Fatma ŞENGÜL What is Chemistry? Chemistry is the area of science that focuses on the properties, composition and structure of elements and compounds. Chemistry also studies the transformations and changes of these substances that th...

MOLECULE CONCEPT and CHEMICAL BONDS Dr. Göksemin Fatma ŞENGÜL What is Chemistry? Chemistry is the area of science that focuses on the properties, composition and structure of elements and compounds. Chemistry also studies the transformations and changes of these substances that they undergo. Chemistry also investigates the large-scale production methods. 2 What is Chemistry? There are five main branches of chemistry: ORGANIC CHEMISTRY: Study of structure, properties, composition, reactions and preparation of carbon-containing compounds. INORGANIC CHEMISTRY: Study of remaining (non-carbon containing) subset of compounds. ANALYTICAL CHEMISTRY: Study of obtaining, processing and communicating information about the composition and structure of matter. 3 What is Chemistry? There are five main branches of chemistry: PHYSICOCHEMISTRY: Study of macroscopic, atomic, subatomic and particulate phenomena in chemical systems in terms of the principle, practices and concepts of physics such as motion, energy, force, time, thermodynamic, quantum chemistry, statistical mechanics, chemical equilibrium and analytical dynamics. Physical chemistry also focuses on states of matter. BIOCHEMISTRY: Study of chemical reactions that take place in the living organisms, in turn, their functions, effects and ways to control them. Sub-disciplines related to these branches of chemistry: polymer chemistry, environmental chemistry, 4 petroleum chemistry, corrosion chemistry, thermochemistry, electrochemistry and others. The History of Chemistry: French chemist Lavoisier who lived in 18th century, is considered as the founder of the modern chemistry. Lavoisier discovered that air consists of various gases, explained the combustion phenomenon and simplified the language used in chemistry. Lavoisier found names and symbols for 33 elements and arranged them into four groups including gases, metals, nonmetals and earths. 6 Chemistry and Human being Chemistry mainly is interested in the building blocks of matter. Thus, chemistry contains direct relationship with all branches of science. The chemical composition of man, the most advanced and complicated being on earth: Phosphorus 700 g, Hydrogen 7000 g, Nitrogen 2100 g, Sulfur 175 g, Oxygen 45500 g, Chlorine 105 g, Carbon 12060 g, Magnesium 35 g, Iron 2,8 g, Potassium 245 g, Calcium 1050 g. 7 Structure of Matter Matter: Granular structure Hallow (void) structure Mobile structure 8 Structure of Matter If the matter is made up of particles, why we cannot see the particles? The presence of 2x1021 water molecules (H2O) in one drop of water explains why the particles that make up water cannot be seen with the naked eye. 9 Structure of Matter Particles of matter: – Atoms – Molecules – Ions 10 Structure of Matter An iron rod, mercury in a bottle, a copper vessel, an aluminum frame are examples of substances whose particles are atoms. Water (H2O), alcohol (C2H5OH), acetone (C3H6O), tea sugar (sucrose, C12H22O11) and oxygen (O2) particles in a tube are examples of molecules. 11 Structure of Matter Examples of substances whose particles are ions: Sodium chloride (table salt) NaCl Na+, Cl- Calcium carbonate (limestone) CaCO3 Ca2+, CO32- Sodium carbonate (washing soda) Na2CO3 , 2Na+, CO32- 12 Structure of Matter Hollow (void) structure of matter: When 50 mL of water is mixed with 50 mL of alcohol, the total volume of solution is always less than 100 mL (approximately 90- 95 mL). How can this situation be explained? The same situation can be also observed for granular materials such as chickpea-rice mixture etc. 13 Structure of Matter Mobility of particles The mobility of particles can be easily detected especially when the gas state of substance is considered. If the gaseous particles of substances were not mobile, could it be possible to understand at the entrance of the apartment which food was cooked in the house? 14  States of Matter State of matter is the form of matter that can exist in the life. States of matter: – Solid (s) – Liquid (l) – Gas – Plasma 15 States of Matter Plasma state of matter: Plasmas are mixture of ions, electrons and neutral atoms moving randomly where collisions at the atomic and molecular levels play a crucial role. The ions and electrons interact through long-range Coulomb forces, whereas neutral atoms and molecules interact by means of short- range collisions. Plasma state of matter is typically an electrically neutral medium of unbound positive and negative particles so that overall charge of plasma is roughly zero. 16 States of Matter Plasma state of matter: A plasma state of matter is observed at very high temperature and pressure. The flame of match and luminescent substance in a burning fluorescent lamp can be given as an example of the plasma state of the matter. 17  States of Matter Three states of water molecule H2O(s) H2O(l) H2O(g) 18  Energy Involvement in Phase Changes Energy Gas release (exothermic) Vaporization Condensation Liquid Melting Freezing (Fusion) Energy Solid requirement (endothermic) 19 Matter Matter Matter is anything that has mass and occupies space. Mass Mass is a measure of the amount of matter in a substance. Weight Weightis the force of gravity on an object and can be calculated as the mass times acceleration of the gravity, w = mg. 20 CLASSIFICATION OF MATTER 21 Matter All matters are composed of elements. Elements are made up of single atoms and the basic building blocks of matter. There are approximately 111 elements in nature. Human body is mainly comprised of six elements mostly carbon (C), hydrogen (H), oxygen (O) and nitrogen (N), but also sulfur (S) and selenium (Se) elements. 22 Chapter 2 23 Pure Substance (Matter) Element – Elements cannot be broken down into simpler substances by chemical reactions. Elements are made up of a single kind atoms to form matter. – For example: Hydrogen (H) and oxygen (O) Compound – Compound is a substance formed by the combination of two or more elements in a chemically fixed proportion. – For example: Water - H2O 24 Mixtures 25 PRECISION and ACCURACY IN MEASUREMENTS 27 SI UNITS FOR MEASUREMENTS Base quantity Unit Abbreviation Mass kilogram kg Length meter m Time second s Temperature kelvin K Electric current ampere A Amount of substance mole mole Luminous intensity candela cd 28 Physical quantity SI unit Area m2 Volume m3 Density kg/m3 Velocity m/s Acceleration m/s2 Power kg * m/s2 ( = newton, N) Pressure kg/(ms2) ( = pascal, Pa) Energy kg * m2/s2 ( = joule, J) 29 Prefix Abbreviation Number Meaning Exponential Multiplier tera T 1,000,000,000,000 trillion 1012 giga G 1,000,000,000 billion 109 mega M 1,000,000 million 106 kilo k 1,000 thousand 103 hecto h 100 hundred 102 deka da 10 ten 101 ----- ---- 1 one 100 deci d 0.1 one in ten 10-1 centi c 0.01 one in hundred 10-2 milli m 0.001 one in thousand 10-3 micro   one in a million 10-6 nano n 0.000000001 one in a billion 10-9 pico p 0.000000000001 one in a trillion 10-12 femto f 0.000000000000001 one in a quadrillion 10-15 30 TEMPERATURE UNITS Temperature unit conversions 31 Basic structure of matter: Atom  History of Atom Democritus (460-370 BC) Original description of atomic concept Dalton (1766 - 1844) 1803 Dalton’s Atomic Theory Crookes (1837-1919) 1879 Discovery of negative charge on cathode rays J.J. Thomson (1856-1940) 1897 Discovery of electrons Millikan (1868-1953) 1909 Discovery of elementary charge in an electron Rutherford (1871-1937) 1911 Discovery of tiny, dense and positively charged nucleus 33 ATOMS and MOLECULES Living organisms and non-living things in the universe are composed of elementary particles called as atoms. The differences of all these beings are derived from the diversity of atoms that they consist of and the combination of these atoms with different bonds. The number of smaller particles, protons (is considered atomic number) differentiates one from the another. 34 Atomic Structure Atom is the smallest unit of an element that show all of its chemical properties. Atoms consist of smaller particles which are electrons, protons and neutrons: Particle Symbol Charge electron e- -1 proton p +1 neutron n 0 35 Structure of Atom Atom is a complex arrangement of; small, dense and positively charged nucleus. Protons and neutrons are located in the positively charged nucleus. small negatively charged subatomic particles, electrons are scattered around the nucleus. 36  Substructures of Atom College Physics. Authored by: OpenStax College. Located at: http://cnx.org/contents/031da8d3-b525-429c-80cf- 6c8ed997733a/College_Physics. License: CC BY: Attribution. License Terms: Located at License. 37 Structure of Atom The nucleus is the small densely packed center of the atom, containing protons and neutrons. The nucleus of the atom would be a pea in the center of the football stadium and the electrons would be whizzing around the outer stands. The mass of the nucleus of an atom is greater than 30 million tons. 38 RELATIVE ATOMIC SIZE OF THE MAIN GROUP ELEMENTS The radii given in picometer 39  Basic Model of an Atom and Atomic Theory Basic model of atom is sometimes also called as Bohr’s atomic model. According to Bohr model; Electrons encircle the nucleus of the atom in specific allowable paths, known as orbit. When the electron is in one of these orbits, its energy is fixed. Energy of an orbital can be determined solely by principal quantum number. 40  Bohr Model of the Atom Small, dense and spherical center of an atom and contains the Nucleus proton and neutrons. Proton Positively electrical charge of one (1+) with a mass of one atomic mass unit (amu), corresponding to about 1.67x 10-27 kg. Neutron No charge (neutral, uncharged) with a mass of one amu. Electron Negatively electrical charge of one (1-) with a mass of 9.1 x 10-31 kg, which only 1/1.836 the mass of a proton. Shell Electrons in an atom are arranged in shells (orbits) that surround the nucleus. 41 Bohr Model of the Atom e- e- e- e- Protons positive e- e- Neutrons neutral e- e- e- e- 42  Bohr Model of the Atom Atomic number is the number of proton in an atom. Each element has a different atomic number. – In another word, each element has a different number of protons. 1 atomic mass unit (AMU) = proton + neutron – 1 AMU = defined as one twelfth (1/12) the mass of an unbound neutral atom of carbon. – 1 AMU = 1,67x10-24 gram. Atoms that contain the same number of protons, but different number of neutrons are called as isotopes. The numbers of protons and neutrons are summed up to name the isotopes of elements. 43 Atomic Properties atomic number = proton number atomic mass, mass number of an atom = total numbers of protons and neutrons The results of atomic reactions: An atom can gain, lose or share their electrons. Two or more atoms come together to form molecules or compounds. All reactions occur through intermolecular or intramolecular interactions at the atomic level. 44  Atomic Symbol A C Z X # A (Atomic mass) : proton + neutron Z (Atomic number): proton number C (charge) : + or - values # The number of atoms in the formula of molecule 45  Atomic Symbol The atomic symbol representation provides information about the proton, neutron and electron numbers of an atom. 31 138 238 15 P 56 Ba 92 U 46  Isotopes An atom contains the same number of protons, but different numbers of neutrons thereby having different mass numbers, AMU. For example, The atomic number of C is 6. Carbon contains 6 proton. The atomic mass of C is either 12 or 14. – C12 = 6 proton + 6 neutron – C14 = 6 proton + 8 neutron – C12 and C14 are isotopes of carbon atom. 47  Isotopes Isotopes: Isotopes are the atoms of the same element with different atomic mass. Isotopes contain the same number of protons, but different numbers of neutrons. Isotopes of hydrogen 1 2 3 H H H 1 1 1 Isotopes of carbon 12 13 14 C C C 6 6 6 48  Isotopes Most elements are naturally found in a mixture of its several isotopes on earth. – Element Number of stable isotopes H 2 C 2 O 3 Fe 4 49  Shells (Orbits) Electrons are found in orbits (shells) around the nucleus. The first shell contains 0e-, 1e- or 2e-, while The second shell contains 0e-, 1e-, 2e-, 3e-, 4e-, 5e-, 6e-, 7e-, or 8e-. Afterwards, 3rd and 4th shells are filled up with electrons. An atom can have maximum of 7 shells. The energy level of an electron shell increases as distance from the nucleus increases, there is a decreased interaction of electron(s) with the nucleus. The max number of electrons in an energy level can be calculated by 2n2 formula. 50  Cloud or Orbital Model According to orbital model, electrons in orbits move in a volume. The density of electrons increases as getting close to the nucleus. The electron shells from nucleus to outer shells are ordered as s, p, d and f orbitals. 51  Neutral Atoms Neutral atom has equal magnitude of negative and positive charges which cancel each other and makes a neutral atom uncharged. An atom with atomic number 6 contains 6 proton. The electron number of this neutral atom is also 6. 52 Electron Configuration The electrons in atoms are arranged in shells that surround the nucleus. Each shell contains a fixed number of electrons due to the size limitation of it. The number of electrons increases as the number of outer shell increases. 53 Electron Configuration Atoms contain nucleus at the center. Nucleus is a tiny, dense, central core of atom which is composed of protons and neutrons. 54 Core and valence electrons Valence electrons Valence electrons are outer shell electrons of an atom and participate the formation chemical bonds. Core electrons Core electrons are the electrons other than valence electrons of the atom and they are tightly bound to the nucleus. They play a role in determination of the chemical reactivity. 55 Energy levels in atoms Each principal energy level can contain up to 2 n2 electrons when n is the number of the level. – The max number of (e-) = 2 n2 Shell Maximum numbers of (n) (e-) 1 2 2 8 3 18 4 32 56 Octet Rule Atoms gain or lose electrons to acquire 8 electrons in their outermost energy level so that they become more stable. H and He do not follow the octet rule. When atoms; Lose or gain e- forming (ionic compounds) Share e- forming (covalent compounds) 57 Chemical Compound Formula Chemical formula of a compound is a symbolic representation of its chemical representation. Chemical formula shows the list of element in the compound. Chemical formula shows how many elements are there in the given compound or molecule. H2O - water CH3CH2OH – ethyl alcohol 2 hydrogen 2 carbon, 6 hydrogen 1 oxygen and 1 oxygen 58 Chemical Compound Formula Hydrogen peroxide = H2O2 Benzene = C6H6 Glucose = C6H12O6 59 Molecular formula of compounds H2O - water CH3CH2OH – ethyl alcohol 60 Types of Molecules Monoatomic contains only one atom Homoatomic consists of atoms of the same element Polyatomic Composed of at least two or more elements in a stable structure. 61 Radioactivity Radioactivity can be defined as the spontaneous emission of high-energy particles or rays from the nuclei of some atoms. The term radioactivity and radioactive elements were first described by Henri Becquerel in 1896. 62 What is radioactivity? Radioactivity can be defined as the spontaneous emission of high energy particles or rays from the nuclei of some atoms. 63 Types of radioactive emissions Rutherford first identified three main types of radioactive emissions which are: 1. Alpha rays (a, ⍺) 2. Beta rays (b, β) 3. Gamma rays (g, ɣ) 64 Penetrating power of radioactivity a b g 0.01 mm 1 mm 100 mm 65 Penetrating power of radioactivity Ionization power = a > b > g Penetrating power = a < b < g 66 Electromagnetic Spectrum 67 Periodic Properties of Elements  The order of elements in the periodic table Mendeleev’ periodic table in 1871 – “Elements were arranged on the basis of fundamental property, atomic mass and chemical properties.” »Periodic table; – provides information about - chemical properties, - chemical reactions and - groups different elements with similar properties. 69  Development of Periodic Table Over Time How more than 110 elements can be arranged in a table? – This problem was first solved by the Russian chemist Mendeleev and the German chemist Meyer. – These scientists first classified the elements based on their similar physical and chemical properties. 70 The ordering of elements Based on the recordings of 2015, there are 118 elements in total. Moreover, most of these elements are discovered between 1735-1843. 71  Periodic Table H He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K Ca Sc Ti V CrMn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn Fr Ra Ac Rf Du Sg Bo HaMe 110111 Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Th Pa U Np PuAmCm Bk Cf Es FmMd No Lr 1700 - 1750 1850 - 1900 Before 1600 1750 - 1800 1900 - 1950 1600 - 1700 1800 - 1850 1950 - 2000 72 Periodic Table: General names of elemental groups Alkali metals I A II A Alkaline earth metal III A IV A V A VI A VIIA VIIIA H He Halogens Li Be Noble gases B C N O F Ne Na Mg III B IVB V B VIB VIIB VIII B IB IIB Al Si P S Cl Ar K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn Fr Ra Ac Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr 73 List of name of chemical element 74 Properties of Periodic Table The elements in periodic table are arranged based on their chemical properties such as reaction types and reactivity and their physical properties such as boiling points and melting points. The elements of periodic table are organized by; – Atomic size (atomic radius) – Ionization energy (the amount of energy required to remove an electron from an isolated atom or molecule) – Electron affinity (the amount of energy required for an electron to be added to a neutral atom in a gas form) – Ionic size (ionic radius) 75 PERIODIC TABLE INFORMATION ABOUT ELEMENT Chemical symbol Chemical activity Atomic number Energy level Atomic mass Electron configuration Proton number Chemical properties Physical state at RT Electron number Oxidation state Neutron number Characteristics of metal and nonmetal 76 Periodic Table Properties All elements are arranged from left to right and top to bottom in order of atomic numbers in the periodic table. GROUP: The vertical columns on the periodic table are called as groups because of their similar chemical properties. The members of group of elements have the same numbers of valence electrons. PERIOD: Horizontal rows are known as period and moving from left to right across a same period, atoms become smaller and electrons move close to the nucleus, thereby increasing the electron affinity from left to right. 77  ORBITAL BLOCKS s-block: All of the elements in the first two columns on the left side of the periodic table are filling the s orbital of their highest energy level with their final electron. – s-block elements in the first two columns on the left side of the periodic table (IA and IIA groups). p-block: Elements contain valence (highest energy) electrons in the p-orbitals. – p-block elements are IIIA, IVA, VA, VIA, VIIA and VIIIA groups in the periodic table. d-block: – d-block elements are IIIB, IVB, VB, VIB, VIIB, IB and IIB groups in the periodic table. f-block: Elements are also known as inner transition metals because of their placement in the periodic table. They contain the lanthanides, and actinides, whose atomic number ranges from 89-111. 78 ORBITAL BLOCKS s- and p-blocks elements in the periodic table are also known as main group elements and their groups are represented by prefixing their group numbers with the letter ‘A’, such as 1A, 2A, 3A, 4A, 5A, 6A, 7A and 8A groups. d and f block elements are also called as side groups and they are presented by prefixing their group numbers with the letter ‘B’ such as 2B and 3B groups in the periodic table. 79 80 Chemical Bonds Chemical Bonds A chemical bond can be established between atoms when they lose, acquire or share electrons. The bonding of atoms is directly related to the numbers and configuration of electrons. There are basically two types of chemical bonds : Intramolecular bonds Intermolecular bonds 82  Intramolecular Bonds Transfer of electrons attraction Ionic Bond + - cation anion Sharing of electrons Chemical bond Covalent ⚫⚫ Bond ⚫ ⚫ H Cl ⚫ ⚫⚫ Metallic Bond Bonding electrons 83 Ionic Bond Ionic bond is a type of linkage formed from the electrostatic attraction between oppositely charged, positive (cation) and negative (anion) ions in a chemical compound. Sodium ion, Na+, — positive (cation) charge Chloride ion, Cl–, — negative (anion) charge 85 Ionic Bond Properties Ionic bond is formed when electrostatic forces in different directions attract each other. The complete transfer of one or more electrons from one atom to the other takes place in a pure ionic bond. In summary, ionic bond is based on transfer of electrons and is the attraction between positive and negative ions. 86 Electron transfer in NaCl Na is a metal. Cl is a non-metal element. Na (metal) transfer its one electron to Cl (non-metal) atom. Because; – The electron configuration of Na is 2-8-1. It is easier to donate one electron rather than acquiring seven electrons for Na metal. – The electron configuration of Cl is 2-8-7. It is easier to obtain one electron from Na to complete its octet. 87 Sodium and Chlorine Na is converted to Na+ cation; Cl, is converted to Cl- anion. Na+ and Cl- complete their octets, Na+ contains 10 e- and Cl- contains 18 e- in total in NaCl e- compound. e- e- e- e- e- e- e- e- e- e- e- e- 11 P+ 17 P+ e- e- e- e- e- 12 N e- 18 N e- e- e- e- e- e- e- e- e- 88 Potassium and Chlorine K is converted to K+ cation; Cl, Cl- is converted to anion. K+ and Cl- complete their octets, K+ contains 18 e- and Cl- contains 18 e- in total in KCl compound. e- e- e- e- e- e- e- e- e- e- e- e- e- e- 19 P+ 17 P+ - e e - e - e- e- e- e- e- 18 N 20 N e- e- e- e- e- e- e- e- e- e- e- e- e- e- 89 Covalent Bonds Covalent bonds are formed by sharing electrons to form electron pairs between atoms. Single covalent bond is formed when a pair of electron is shared. Double covalent bond is formed as a result of sharing two pairs of electrons. Triple covalent bond is formed when three pairs of electrons are shared. 91 Single Covalent Bond e- 1 P+ 1 P+ e- Two hydrogen atoms share a pair of electrons to form single covalent bond and form H2 molecule. 92  Double Covalent Bonds 0=0 structural e- e- formula e- e- e- e- 8 P+ 8 P+ e- 8N e- e- e- e- 8N e- e- 02 molecular formula e- e- e- Two oxygen atoms share two pairs of electrons to form double covalent bond and to form 02 molecule. 93  Triple Covalent Bond e- structural e- formula e- e- 7 P+ 7 P+ e- 7N e- e- e- e- 7N e- e- e- N2 molecular e- e- formula Both nitrogen atom contains 5 electrons in the outermost shell. Two nitrogen atoms require 3 electrons to achieve their octet configurations so that they shares three pairs of electrons to form triple covalent bonds and to form N2 molecule. 94  Methane: Four single covalent bond P+ e- e- P+ e- 6P+ e- P+ e- e- e- e- 6N structural formula e- e- P+ CH4 – molecular formula 95 Polar Covalent Bonds Polar covalent bonds are formed typically between different atoms in a molecule. Therefore, atoms with different electronegativities share electrons in a covalent bond. While there is no net charge difference in the molecule, sharing of electrons occurs at the atomic level. Water (H2O) is an example of polar covalent bond. 96 Oxygen and Hydrogen Water is a typically polar molecule due to the significant unequal sharing of electrons between hydrogen and oxygen atoms. The unequal sharing of electrons makes H2O molecule slightly negative near oxygen atom and slightly positive near its hydrogen atoms. P+ P+ e- - e- e e- e- e- 8P+ e- e- 8N H + H H2O Water e- e- O molecular formula - structural formula 97 Intermolecular Bonds (Interactions) Differences in physical properties such as melting or boiling points are affected by intermolecular forces. Five major types of intermolecular forces (interactions): – Ion-ion interactions, – Dipole-dipole interactions, – Ion-dipole interactions, – London forces, – Hydrogen bonds 98 Intermolecular Forces: Differences in physical properties such as melting or boiling points are determined by intermolecular forces between molecules. 99 Intermolecular Forces: Five major types of intermolecular forces: Ion-ion interactions Dipole-dipole interactions Ion-dipole interactions London forces Hydrogen bonds 100 Ion-Ion Interactions Ion-ion interaction is defined as electrostatic attraction between positively-charged cation ion and negatively-charged anion ion. Na+ and Cl- ions stack on each other in NaCl salt. Ion-ion interactions are weaker than hydrogen, metallic, covalent and ionic NaCl: Ionic interaction bonds. forming solid salt crystals. The repeating ionic interactions in NaCl form solid salt crystal structure. 101 Ionic solids: Ionic solids melt at high temperatures and boil at even higher temperatures : – NaCl mp = 801 °C; bp = 1413 °C – KCl mp = 776 °C; bp = 1500 °C – MgO mp = 2800 °C; bp = 3600 °C 102 Dipole-Dipole Interactions Dipole-dipole interactions are encountered between polar molecules. Dipole-dipole interactions are weaker than ion-ion interactions. 103 Ion-Dipole Interactions Ion-dipole + interactions are an attractive force that results from the electrostatic attraction between an ion and a neutral molecule containing - dipole. 104 Ion-Dipole Interactions A positive ion (cation) attracts partially + negative end of a neutral polar molecule. A negative ion (anion) - attracts partially positive end of a neutral polar molecule. 105 London Forces London dispersion forces can be described as a temporary attractive force due to the formation of temporary dipoles in a nonpolar molecule. When electrons in two adjacent atoms are displaced in such a way that atoms get some temporary dipole moments, they attract each other through London forces. 106 London Forces London forces are the weakest intermolecular interactions. London forces increase with the increase in molecular mass and in numbers of electrons. 107 Hydrogen Bonds Hydrogen bond is an intermolecular force that are formed as a result of interaction of hydrogen with highly electronegative atoms including F, O and N. For example - H2O, DNA Hydrogen bonds in water also gives the characteristic feature of water as follows: Surface tension Fluidity (viscosity) Vapor pressure. 108 Hydrogen Bonds Hydrogen bonds are formed between hydrogen atoms of one water molecule and oxygen atom of a neighboring water molecule. 109 Hydrogen Bonds Hydrogen bond is a special type of dipole- dipole interaction that occurs between the lone pair of a highly electronegative atoms typically F, O and N, and H atom a F-H, O-H and N-H bond. Hydrogen bonds are weak intermolecular interaction than intramolecular bonds. 110  Hydrogen Bonds Hydrogen bonds are stronger than London forces, ion-ion interactions and dipole-dipole interactions. 111