General Chemistry for Pharmaceutical Sciences Part I Final 5.pdf
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General Chemistry for Pharmaceutical Sciences PHARM-101 Presented by Dr. Azza H. Rageh Associate Professor of Pharmaceutical Analytical Chemistry Office: College of Pharmacy Department of Pharmacognosy and Pharmaceutical Chemistry Building 15 – O...
General Chemistry for Pharmaceutical Sciences PHARM-101 Presented by Dr. Azza H. Rageh Associate Professor of Pharmaceutical Analytical Chemistry Office: College of Pharmacy Department of Pharmacognosy and Pharmaceutical Chemistry Building 15 – Office 106 References Raymond Chang (2015). Chemistry: 12th ed., McGraw- Hill education, Boston, New York, U.S.A. Janice Smith (2022). General, Organic & biological Chemistry, 5th edition McGraw-Hill education, Boston, New York, U.S.A. Theodore E. Brown, H. Eugene LeMay, Bruce E. Bursten, Catherine Murphy, Patrick Woodward, Matthew E. Stoltzfus (2019), Chemistry: The Central Science, 13th ed. , Pearson, UK. A- Matter and Measurements 1- Classification and States of Matter The Chemical World Chemistry: The science that seeks understanding the properties and behavior of matter by studying atoms and molecules. - Chemistry is central to understand many other scientific fields. - Virtually, everything around you is composed of “chemicals”. 5 Chemistry: The Central Science 6 Atoms and Molecules ⮚ Atoms are the building-blocks of matter. ⮚ Each element is made of a unique kind of atoms (so far, 120 elements are identified in the universe, they are represented in the periodic table of elements). ⮚ The compound is made of two or more atoms of different elements, bonded together to form molecules (molecules are the building-blocks of compounds). ⮚ The properties of a substance are determined by the properties of its constituent molecules and atoms. 7 Atoms and Molecules Important Note: some elements are present as “molecules” instead of “free atoms”, they are called: “Molecular Elements”, such as: H2, N2 , O2 , F2 , Cl2 , Br2 , I2 , P4 , S8 , Se8 and O3 (Ozone Gas) 8 Atoms and Molecules Example 1 ✓ The air contains carbon monoxide pollutant. ✓ Each molecule contains a carbon atom and an oxygen atom held together by a chemical bond. 9 Atoms and Molecules Example 2 Note: Balls of different colors are used to represent atoms of different elements. Attached balls represent connections between atoms that are seen in nature. These groups of atoms are called molecules. 10 The Classifications of Matter Matter is anything that occupies space and has mass. Examples: your textbook, your desk, the air around you, and even your body, are all composed of matter. Matter is everything around us. Matter can be classified according to: 1. State (the physical form) 2. Composition (the components that make it up) 11 The States of Matter ⮚ Matter can exist in one of three main states: solid, liquid, or gas. The state of matter changes from solid to liquid to gas by increasing temperature, and vice versa! 12 Solid Matter ⮚ Solid Matter: is composed of tightly packed particles (atoms or molecules). Solids retain their shapes because the particles are not free to move. ⮚ Although the atoms and molecules vibrate in solids, they do not move around or past each other. ⮚ Consequently, solid matter has a fixed (definite) volume and a fixed (rigid) shape. Examples of solids: Ice, aluminum, iron, wood, salt, and diamond. 13 Solid Matter Crystalline or Amorphous? ⮚ Crystalline Solids: atoms or molecules are arranged in “patterns” with a long-range repeating order. Important Examples on crystalline solids: table salt (NaCl) and diamond. ⮚ Amorphous Solids: atoms or molecules are not arranged in long-range patterns. Important Examples on amorphous solids: graphite, rubber, glass and plastic. 14 Liquid Matter ⮚ Liquid Matter: is made of more loosely packed particles than in solids. Particles can move about within a liquid, but they are packed densely enough that volume is maintained. ⮚ The ability of liquids to flow, makes them take the shapes of their containers. ⮚ Liquids have fixed volume but no fixed shape. Examples of liquids: water, oil, and gasoline. 15 Gaseous Matter ⮚ Gaseous Matter: is composed of particles packed so loosely that it has neither a defined shape nor a defined volume. ⮚ Particles of gases (atoms or molecules) are free to move relative to one another. ⮚ Gases have no fixed volume and no fixed shape, they take the volume and shape of their containers. These qualities make gases compressible. ⮚ Examples of gases: oxygen, nitrogen, CO2, water vapor 16 Summary of State Changes of Matter 17 Classification of Matter according to its composition ⮚ Matter can be divided into two classes: 1. Mixtures: are composed of more than one substance and can be physically separated into its component substances. 2. Pure substances: are composed of only one substance and can NOT be physically separated. 18 Mixtures There are two types of mixtures: 1. Heterogeneous mixtures 2. Homogeneous mixtures ✓ Heterogeneous Mixture: does NOT have uniform properties throughout. – (sand + water), (oil + water) or (gasoline + water) are examples on heterogeneous mixtures. ✓ Homogeneous Mixture: has uniform properties throughout. – (salt water), (sugar + water) and alloys are homogeneous mixtures. 19 Pure Substances There are two types of pure substances: 1. Compounds 2. Elements ✓ Compound: can be chemically separated into individual elements. There are millions of compounds in the universe. ⮚ Water is a compound that can be separated into hydrogen and oxygen. ✓ Element: cannot be broken down further by chemical reactions. ⮚Elements are the 120 members of the periodic table of elements, such as: Sodium, Iron, Gold, Silver, Hydrogen, Oxygen, Carbon …... etc 20 Summary of Types of Matter Matter can be classified according to its composition into: pure substances (elements or compounds) and mixtures (homogeneous or heterogeneous): 21 Assessment 1) The process is which a solid substance is transformed directly into a gas is called and it requires of temperature. 2) is the physical process which changes a gas into a liquid, and it needs of temperature. 3) Which state of matter has a fixed volume but not a fixed shape? 4) A matter is able to assume both the shape and volume of its container. 5) The ability of both and states of matter to flow makes them able to change their shape to the shape of their reservoir. 6) Classify each substance as a pure substance or a mixture, and indicate the type of a. sweat b. carbon dioxide c. aluminum d. salt e. rust f. wet sand g. air h. oxygen gas i. bronze alloy j. honey 22 A- Matter and Measurements 2- Physical and Chemical Changes and properties 23 Physical and Chemical Changes Physical Changes: A process that does NOT cause a substance to become a different substance (i.e. only the appearance (state or shape) is changed, but NOT the chemical composition). Physical changes are reversible. Example 1: when water (H2O) boils, it changes its state from liquid to gas. ⮚ The gas remains composed of H2O, so this is a “physical change”. Example 2: when a piece of paper is shredded, or a glass window is broken, only their shapes have changed, but their chemical compositions remained unchanged. 24 Physical and Chemical Changes Chemical Changes: A process that causes a substance to change into a new substance with a new chemical composition. During a chemical change, atoms rearrange themselves to make different substances. Chemical changes are irreversible. Example 1: rusting of iron is a chemical change: 4 Fe + 3 O2 → 2 Fe2O3 Example 2: burning of gasoline produces CO2 + H2O, so, it’s a chemical change 25 Evidences for Chemical Changes a) Release of a gas (e.g. bubbles or smoke) b) Emission of light or heat (e.g. burning of wood) c) Permanent change in color (e.g. the brown layer of iron rust) 26 Physical and Chemical Changes Examples 27 Physical and Chemical Properties of Matter Physical Properties: any characteristic that can be measured without changing the substance’s chemical identity or composition (i.e. without any chemical reactions). ⮚ Examples on Physical Properties: ⮚ Color ⮚ Viscosity ⮚ Odor ⮚ Temperature ⮚ Taste ⮚ Hardness ⮚ Density ⮚ Metallic Luster ⮚ Melting Point ⮚ Malleability ⮚ Boiling Point ⮚ Ductility 28 Physical and Chemical Properties of Matter Physical Properties: a r e e i th e r e xte n s i ve o r i n te n s i ve Extensive properties: are that depend on amount of matter to be measured such as mass and volume. Insensitive properties: are that not depend on amount of matter to be measured such as color, taste and density. Classify the following physical properties extensive or intensive. 1. Color (intensive). 2. Density (intensive). 3. Volume (extensive). 4. Mass (extensive). 5. Boiling point (intensive): temperature at which substance boils. 6. Melting point (intensive): temperature at which substance melts. 29 Physical and Chemical Properties of Matter Chemical Properties: any characteristic that can be measured only by changing a substance’s chemical identity or composition (i.e. in a chemical reaction). ⮚ Examples on Chemical Properties: ⮚ Reactivity with other chemicals (acids, water, oxygen, ….) ⮚ Acidity and Basicity ⮚ Flammability: ability of compound to burn when exposed to flame. ⮚ Chemical stability: refers to reactions that alter chemical structures of compounds such as oxidation (reaction with oxygen), hydrolysis (reaction with water) and photosensitivity (decomposition by light). ⮚ Toxicity ⮚ Heat of combustion: Energy released upon complete combustion (burning) of compound with oxygen. ⮚ Oxidation state: It describes the degree of oxidation (loss of electrons) of 30 an atom in a chemical compound Assessment Identify the following as chemical or physical changes or properties: 1. blue color 2. melting point 3. density 4. reaction with water 5. flammability 6. hardness 7. toxicity 8. boiling point 9. reaction with acid 10. luster 11. perfume odor 12. sour taste 13. coal Burns 14. dry ice sublimes 15. Ag (Silver) tarnishes 16. milk sours 17. an apple is cut 18. fruit rot 19. heat changes H2O to steam 20. pancakes cook 21. baking soda reacts to vinegar 22. grass grows 23. iron rusts 24. a tire is inflated 25. alcohol evaporates 26. food is digested 27. ice melts 28. paper absorbs water 31 A- Matter and Measurements 3- Units of Measurements and Density of Materials 32 The Units of Measurement We use measurements in everyday life, for example: walking 2.25 km to the university campus, carrying a backpack with a mass of 12 kg, and observing when the outside temperature has reached 40°C. 33 The Units of Measurement ⮚ Units: standard quantities used to specify measurements, they a r e critical in chemistry. The most common systems of units are: 1. The English system: used in the United States. 2. The Metric system: used in most countries. 3. The International System of Units (SI): used by scientists, and it is based on the metric system. 34 Units in the Metric and SI Systems of Measurement ⮚ In the metric and SI systems, one unit is used for each type of measurement: Measurement Metric System (SI) System Length meter (m) meter (m) Volume liter (L) cubic meter (m3) Mass gram (g) kilogram (kg) Temperature Celsius (°C) Kelvin (K) Time second (s) second (s) 35 The Meter: A Measure of Length (or Distance) Length (or distance): ⮚ Useful relationships between ▪ is measured using a the units of length: meter stick. ▪ The unit meter (m) is used in both the metric and SI systems. ▪ Centimeters (cm) is used for smaller lengths. 36 The Kilogram: A Measure of Mass The mass of an object is a measure of the quantity of matter within it. The SI unit of mass is kilogram (kg): 1 kg = 2.21 lb (pound) 1 gram = 1/1000 kg = (10-3 kg) Weight of an object is a measure of the gravitational pull on its matter: (weight ≠ mass) 37 Units for Volume Measurement ⮚ The common units for volume measurements are: Liter (L), Milliliter (mL), and Cubic Meter (m3) ⮚ Useful relationships between the units of volume: 1 L = 1000 mL 1000 L = 1 m3 38 Some Lab Tools for Volume Measurement ⮚ Volume is the amount of space occupied by a substance. 39 Unit of Time Measurement Time measurement: ▪ uses the unit second (s) in both the metric and SI systems. Days, Hours, Minutes, Seconds ⮚ Useful relationships between the units of time: 40 Unit of Temperature Measurement ⮚ Common Units of Temperature: – Fahrenheit (oF) (English system). – Celsius (oC) (Metric system). – Kelvin (K) (SI system). ⮚ Example 1: Boiling Point of Water: 212 oF = 100 oC = 373.15 K ⮚ Example 2: Freezing Point of Water: 32 oF = 0 oC = 273.15 K 0 K is called: “absolute zero”. It is the lowest possible temperature in the universe! 41 Relationships Between Units of Temperature - From °C to K: K = °C + 273.15 - From K to °C: °C = K – 273.15 - From °C to °F: °F = [1.8 × (°C)] + 32 - From °F to °C: 42 Examples on Temperature Conversions 1. How much does 350 oF equal in both oC and K? oC = (350 − 32)/1.8 = 318/1.8 = 177 oC K = 177 + 273.15 = 450.15 K 2. Convert ( ̶ 40 oC) to oF: oF = [1.8 × (−40)] + 32 = −72 + 32= −40 oF 3. Express 298 Kelvin in degree Celsius: oC = 298 − 273.15 = 24.85 oC 43 Prefix Multipliers: Changing The Value of The Unit ⮚ The International System of Units (SI) uses the prefix multipliers with the standard units. These prefix multipliers change the values of the units (make units larger or smaller). Examples: - the kilometer has the prefix kilo, meaning 1000 meter (or 103 m). - the millimeter has the prefix milli, meaning 1/1000 meter (or 10−3 m). 44 Prefix Multipliers: Increasing the size of the Unit Prefixes that INCREASE the size of unit: Note: students shall memorize those prefixes: (names, symbols, and factors)! 45 Prefix Multipliers: Decreasing the size of the Unit Prefixes that DECREASE the size of unit: Note: students shall memorize those prefixes: (names, symbols, and factors)! 46 Density of Materials ▪ Material's Density is its mass per unit volume. ▪ Usually measured in g/L, g/mL, or g/cm3. ⮚ Density Expression: Useful Note: 1 mL = 1 cm3 47 Calculating Density – Example If a 0.258 g sample of HDL has a volume of 0.215 cm3, what is the density (in g/cm3), of the HDL? Step 1: State the given and needed quantities: Given Needed 0.258 g HDL density of HDL in g/cm3 0.215 cm3 HDL Step 2: Use the relation: 48 Calculating Density – Example 1. Do the following conversions: a. 55 m = …………… km = …………… cm b. 11 s = …………… ms = …………… ks c. 2.7 g = …………… pg = …………… ng d. 3.6 L = …………… mL = …………… µL 2. Express the temperature −56 °F in both °C and K. 3. Perform each of the following unit conversions: a. 13.53 m to yd b. 2.87 kg to lb c. 2.45 L to m3 d. 123.7 mm to in 4. Calculate the density of penny that has a mass of 2.49 g and a volume of 0.349 cm3. 49 B- Atoms, Molecules, Ions and Periodicity 1- History of Atomic Structure, Modern Atomic Theory and Atomic structure History of Atomic Structure ▪ The word atom comes from the ancient Greek adjective atomos, meaning "indivisible”. indivisible : unable to ▪ Atom is smallest constituent of matter and be divided or separated consists of nucleus and surrounding electrons. ▪ The nucleus is made of one or more protons and typically a similar number of neutrons. ▪ Every atom is composed of a nucleus and one or more electrons bound to the nucleus 51 History of Atomic Structure ▪ Protons and neutrons are called nucleons. More than 99.94% of an atom's mass is in the nucleus. ▪ The protons have a positive electric charge, the electrons have a negative electric charge, and the neutrons have no electric charge. ▪ If the number of protons and electrons are equal, that atom is electrically neutral. ▪ If an atom has more or fewer electrons than protons, then it has an overall negative or positive charge, respectively, and it is called an ion. 52 History of Atomic Structure 53 How Electrons are Arranged in Atom? Electrons are arranged in orbitals (s, p, d, and f). An orbital can hold a maximum of two electrons. Orbitals are grouped in shells designated by numbers 1, 2, 3, and so on. Valence electrons are located in the outermost shell. Electrons in shells that are not completely filled. 54 How Electrons are Arranged in Atom? Electron arrangement (orbital diagram and electron configuration) of: 1H 10Ne 2He 15P 6C 16S 7N 17Cl 8O 18Ar Example: Orbital Diagram Electron configuration and orbital diagram of fluorine 9F Electron configuration 9F 55 Modern Atomic Theory and Laws that Led to It The theory that all matter is composed of atoms grew out of many observations and laws. The three most important laws that led to the development and acceptance of the atomic theory are: Law of conservation of mass Law of definite proportions Law of multiple proportions 56 Law of Conservation of Mass Law of Conservation of Mass (A. Lavoisier): Matter is neither created nor destroyed in a chemical reaction. Total mass of used reactants = Total mass of produced products Total number of reactants’ atoms = Total number of products’ atoms 57 Law of Definite Proportions Law of Definite Proportions (J. Proust): A given chemical compound always contains the same elements in the exact same proportions (by mass), regardless to its source or how it was prepared For example: Sodium chloride (NaCl) always has a definite mass-to- mass ratio of chlorine and sodium. This ratio is always the same for any sample of pure NaCl, regardless of its origin: A 100 g sample of NaCl contains 39.3 g Na & 60.7 g Cl 𝑴𝒂𝒔𝒔 𝑪𝒍 𝟔𝟎.𝟕 𝒈 = = 𝟏. 𝟓𝟒 𝑴𝒂𝒔𝒔 𝑵𝒂 𝟑𝟗.𝟑 𝒈 A 58.44 g sample of NaCl contains 22.99 g Na & 35.44 g Cl 𝑴𝒂𝒔𝒔 𝑪𝒍 𝟑𝟓.𝟒𝟒 𝒈 = = 𝟏. 𝟓𝟒 𝑴𝒂𝒔𝒔 𝑵𝒂 𝟐𝟐.𝟗𝟗 58 Law of Multiple Proportions Law of Multiple Proportions (J. Dalton): When two elements, “A” and “B”, combine with each other to form two or more compounds, the ratios of the masses of those elements in the formed compounds are simple whole numbers. For example: – A molecule of carbon dioxide (CO2) has a ratio of 1 C atom to every 2 atoms of oxygen, or 1:2. – A molecule of carbon monoxide (CO) has a ratio of 1 C atom to 1 atom of oxygen, or 1:1. Another Example: “Fe” to “O” in FeO = (1:1), while in Fe2O3 = (2:3) 59 Dalton’s Atomic Theory Postulates of Atomic Theory of Matter (J. Dalton): Each element is composed of tiny, indestructible particles called atoms. An element’s atoms are identical in size, mass and all other properties. Atoms of different elements vary in size and mass. Atoms of one element cannot change into atoms of another element. Atoms are indivisible and the chemical reaction leads to rearrangement of atoms not to their creation or destruction. Molecules are simple whole-number ratios of the combined elements 60 Elements: Defined by their Number of Protons Each element has a unique name, symbol, and atomic number. – Symbol has either one or two letters: O (oxygen) or Fe (iron) – The elements are arranged on the periodic table in order of increasing their atomic numbers. 61 Elements: Defined by their Number of Protons The number of protons located in an atom’s nucleus determines the element’s identity. – The number of protons in the nucleus of an atom is called the “atomic number” and is referred to as “Z”, it’s considered as the “fingerprint” of any element. 62 Isotopes: When The Number of Neutrons Varies Isotopes: are atoms of one element that have the same number of protons (atomic number) and different number of neutrons. – Isotopes differ in mass number because they have different number of neutrons. – Isotopes are chemically identical, but may be physically different. Mass Number (A) = Protons + Neutrons Note: Isotopes are identified by their “mass numbers” (example: C–12 , C–13 , C–14) 63 Isotopes: An Example Carbon-12 Carbon-13 Carbon-14 12C 13C 14C 6 6 6 protons: 6 p+ 6 p+ 6 p+ neutrons: 6 n 7n 8n electrons: 6 e- 6 e- 6 e- 64 Exercise How many protons, electrons, and neutrons are in the following atoms: protons electrons neutrons 32 S 16 65 Cu 29 U–240 Note: Neutral atoms have the same number of electrons as protons! 65 Exercise The Answer: How many protons, electrons, and neutrons are in the following atoms: protons electrons neutrons 32 S 16 p 16 e 32 16 = 16 n 16 65 Cu 29 p 29 e 65 29 = 36 n 29 92 U–240 92 p 92 e 240 92 = 148 n (Isotope) 66 Molecules ▪ Molecules are neutrally charged species and has no charge e.g. HCl if compared to ions. ▪ A molecule is an electrically neutral group of two or more atoms held together by chemical bonds. Molecules are distinguished from ions by their lack of electrical charge. ▪ A molecule may be homonuclear, that is, it consists of atoms of one chemical element as with oxygen (O2); or it may be heteronuclear, a chemical compound composed of more than one element, as with water (H2O). 67 Ions: Charged Atoms (Cations vs. Anions) Cations Anions A CATION forms when an atom loses An ANION forms when an atom gains one or more electrons from its outer one or more electrons into its outer shell (valence shell, the highest shell (valence shell, the highest energy level). energy level). Cations are positively charged Anions are negatively charged because the atom has more protons because the atom has fewer protons (+) than electrons (–). (+) than electrons (–). – Mg atom has 12 protons & 12 electrons. – F atom has 9 protons & 9 electrons. – Mg2+ ion has 12 protons & 10 electrons. – F – ion has 9 protons & 10 electrons. Metal elements tend to form cations. Nonmetal elements tend to form anions. Example: Mg Mg2+ + 2 e – Example: F + 1 e– F– 68 Ions: Charged Atoms (Cations vs. Anions) 69 Ions: Zwitter Ion (Charged Molecules) Zwitter ions: Neutral molecules although it has positive and negative ions at different positions Ex. 1: most amino acids +NH 3-CH2-COO - Ex. 2: Pregabalin A medication used for treatment of epilepsy and anxiety 70 Assessment Answer the following questions: 1- Fill in the blanks to complete the table: 2- Determine the number of p+, n0, and e¯ in each atom: 3- Determine the number of protons and the number of electrons in each ion: 4- Write isotopic symbols of the form for each isotope: a. the copper isotope with 36 neutrons b. the oxygen isotope with 8 neutrons c. the aluminum isotope with 14 neutrons d. the iodine isotope with 74 neutrons 71 B- Atoms, Molecules, Ions and Periodicity 2- The Periodic Table of Elements The Modern Periodic Table In 1913, Henry Moseley proposed the modern periodic table using atomic number instead of atomic mass, as the organizing principle for all the identified elements. The Modern Periodic Table Consists of: 7 Rows: are referred to as Periods, the periods are numbered 1–7. 18 Columns: are sometimes referred to as Groups or Families, they are numbered 1–18 (or the A and B grouping). – They are commonly called “Families” because the element within the column have similar physical and chemical properties. 73 Classification of Elements Elements in the periodic table are classified into the following three major divisions: Metals Nonmetals Metalloids 74 The Modern Periodic Table: Metals, Nonmetals & Metalloids 75 Classification of Elements: Metals Metals lie on the lower left side and middle of the periodic table. Properties of Metals: They are good conductors of heat and electricity. All metals are solids at room temperature, except mercury (Hg) is a liquid. They can be pounded into flat sheets (malleability). They can be drawn into wires (ductility). They are often shiny. They tend to lose electrons when they undergo chemical changes (forming cations). About 75% of the elements in the periodic table are metals. 76 Classification of Elements: Nonmetals Nonmetals lie on the upper right side of the periodic table. Properties of Nonmetals: Poor conductors of heat and electricity. Can be found in all three states of matter (gases, liquids & solids). Nonmetals with solid state are brittle (not ductile & not malleable). They tend to gain electrons when they undergo chemical changes (forming anions). 77 Classification of Elements: Metalloids Metalloids are elements that lie along the zigzag line that divides metals and nonmetals in the periodic table. Properties of Metalloids: Can exhibit mixed properties of both metals and nonmetals. Solids at room temperature. Known as semiconductors for electricity. Poor conductors of heat. 78 Major Families: Alkali Metals (Group 1A) Group 1A elements are called the alkali metals, they are highly reactive metals (except hydrogen). Examples: – A marble-sized piece of sodium explodes violently when dropped into water. – Lithium, potassium, and rubidium are also alkali metals. 79 Major Families: Alkaline Earth Metals (Group 2A) Group 2A elements are called the alkaline earth metals. They are fairly reactive, but not quite as reactive as the alkali metals (group 1A). Examples: – Calcium, for example, reacts fairly vigorously with water. – Other alkaline earth metals include magnesium (a common low-density structural metal), strontium, and barium. 80 Major Families: Halogens (Group 7A) Group 7A elements are called halogens, they are very reactive nonmetals. They are always found in nature as salts. Examples: – Chlorine, a greenish-yellow gas with a pungent odor. – Bromine, a red-brown liquid that easily evaporates into a gas. – Iodine, a purple solid. – Fluorine, a pale-yellow gas. 81 Major Families: Noble Gases (Group 8A) Group 8A elements, called the noble gases, are mostly unreactive (inert). Examples: – The most familiar noble gas is helium, used to fill buoyant balloons. – Other noble gases are neon (often used in electronic signs), argon (a small component of our atmosphere), krypton, and xenon. 82 Ions and the Periodic Table Loss electrons Gain electrons +1 +2 +3 -3 -2 -1 In general, the charge of ions of main-group elements can be predicted from their group’s number 83 Assessment Answer the following questions: 1- Which pairs of elements do you expect to be similar? Why? a. N and Ne b. Mo and Sr c. Ar and Kr d. Cl and I e. P and Pd 2- Predict the charge of the monoatomic ion formed by each element: a. O b. K c. Al d. Rb e. N 3- Using a copy of the periodic table, write the name of each element and classify it as a metal, nonmetal, or metalloid: a. Na b. Mg c. Br d. N e. As 7- Using a copy of the periodic table, classify each element as an alkali metal, alkaline earth metal, halogen, or noble gas: a. sodium b. iodine c. calcium d. barium e. krypton 84 C- Molecules, Compounds and Chemical Bonds 1- Chemical Formulas and Molecular Models Elements, Compounds and Mixtures 86 Elements & Compounds Elements are the simplest form of matter, they can combine together to make a limitless number of compounds. The properties of the compounds are totally different from their constituent elements. Example: the properties of water are different from the properties of both H2 and O2: 87 Classification of Organic Compounds According to Functional groups 88 Classification of Organic Compounds According to Functional groups 89 Representing Compounds: Chemical Formulas & Molecular Models A Compound is a distinct substance that is composed of bonded atoms of two or more elements. We can describe the compound by describing the number and type of each atom in the simplest unit of the compound: molecules Each element is represented by its letter symbol (from the periodic table) The number of atoms of each element is written to the right of the element as a subscript (if there is only one atom of an element, the “1” subscript is not written), examples: C6H12O6 , CH3Br Polyatomic ions are placed in parentheses (if more than one). examples: Mg(NO3)2 , Al(OH)3 , NaOH 90 Representing Compounds: Chemical Formulas & Molecular Models Compounds are generally represented with their Chemical Formulas or Molecular Models. Chemical formula indicates the type and number of each element present in the compound (using the letter symbols of the elements from the periodic table): – Water is represented as H2O – Carbon dioxide is represented as CO2 – Sodium chloride is represented as NaCl – Carbon tetrachloride is represented as CCl4 91 Types of Chemical Formulas Chemical formulas can generally be categorized into three different types: 1. Empirical Formula 2. Molecular Formula 3. Structural Formula The amount of information about the structure of the compound varies with the type of formula. All formulas and models convey a limited amount of information – none is a perfect representation! 92 Types of Chemical Formulas: The Empirical Formula Empirical Formula: gives the relative number of atoms of each element in a compound. It does not describe the actual number of atoms, the order of attachment, or the shape of molecules. It is the simplest whole-number ratio representation of the type and number of elements present in a molecule. The Ionic compounds (metal + nonmetal) are usually represented using their Empirical Formulas (formula units): (e.g. MgO not Mg2O2 & CaS not Ca2S2 , …. ) 93 Types of Chemical Formulas: The Molecular Formula Molecular Formula: gives the actual number of atoms of each element in a molecule of a compound. It does not describe the order of attachment, or the shape of molecules. Examples: a) H2O is the molecular formula of water, which means that the water molecule is actually composed of 2 hydrogen atoms + 1 oxygen atom. b) C4H8 is a molecular formula, which means that the molecule is actually composed of 4 carbon atoms + 8 hydrogen atoms. c) B2H6 is a molecular formula, which means that the molecule is actually composed of 2 boron atoms + 6 hydrogen atoms. 94 Types of Chemical Formulas: The Structural Formula Structural Formula: is a sketch or diagram of how the atoms in the molecule are bonded to each other. It uses lines to represent covalent bonds and shows how atoms in a molecule are connected or bonded to each other. lines describe the number of electrons shared by the bonded atoms: Single line = two shared electrons, a single covalent bond Double line = four shared electrons, a double covalent bond Triple line = six shared electrons, a triple covalent bond It’s used only with “Molecular Compounds” (Nonmetal + Nonmetal), but NOT with “Ionic Compounds” (Metal + Nonmetal) Example: The structural formula for CO2 is: Example: The structural formula for methane CH4 is: 95 Molecular Models There are two common molecular models used to represent the molecules of compounds: - Ball-and-Stick Model - Space-Filling Model Example: the different ways to represent the methane molecule (CH4): 96 Exercises: Molecular and Empirical Formulas Exercise: Write the Empirical Formulas for the following compounds: 97 An Atomic Level View of Elements and Compounds 1. Atomic Elements: elements whose particles are single atoms, most of the elements in the periodic table are “atomic elements”: e.g. Fe , Na , Al , Ne , Hg, ….. 2. Molecular Elements: elements whose particles are multi-atom molecules, having the same type of atoms (i.e. atoms of the same element), (atoms are bonded by covalent bond): e.g. H2 , O2 , N2 , Cl2 , P4 , S8 , Se8 …. (see the next slide) 3. Molecular Compounds: compounds whose particles are molecules made of only nonmetals, (bonded by covalent bond): e.g. H2O , NH3 , HCl , CH4 4. Ionic Compounds: compounds whose particles are composed of cations (of metals) and anions (of nonmetals), (bonded by ionic bond): e.g. NaCl , AlF3 , Fe2O3 , Mg2S 98 Molecular Elements Certain elements occur as diatomic molecules (only 7 out of the 118 elements of the periodic table): H2 , N2 , O2 , F2 , Cl2 , Br2 and I2 Some other elements occur as polyatomic molecules: P4 , S8 , Se8 and O3 (Ozone Gas) 99 Classification of Elements and Compounds: A Summary 100 Assessment Classify the following substances as: Atomic Elements, Molecular Elements, Molecular Compounds, or Ionic Compounds: a. Barium, Ba ………………………………………………..……………………………..……. b. Iron(III) chloride, FeCl3 …………………..………………..……………………… c. Bromine, Br2 …………………..…………………………………………………….………… d. Ethanol, C2H6O …………………..………………..…………………………..……...…… e. Nitrogen monoxide, NO …………………..………………………….……..……… f. Cobalt, Co …………………..………………..………………………..……..……...…………… g. Carbon monoxide, CO …………………..……………………….……….………..… h. Nickel(II) chloride, NiCl2, …………………..……………………..……………..… i. Sodium iodide, NaI …………………..………………………………….……………..… j. Phosphorus chloride, PCl3 …………………..……………………..……………..… 101 B- Molecules, Compounds and Chemical Bonds 2- Mole, Molar Mass and Mole conversions 102 Molar Mass Definition of the “Mole” The Molar Mass of a Compound Mole Conversions 103 Formula Mass & Molar Mass Formula Mass (amu): The mass of an individual molecule or formula unit, expressed in “amu” (atomic mass unit) also known as molecular mass or molecular weight. Sum of the masses of the atoms in a single molecule or formula unit Formula mass of H2O = [2 × (1.01 amu H)] + [1 × (16.00 amu O)] = 18.02 amu Molar Mass (g/mol): The mass of one mole of a substance, expressed in “g/mol” Molar mass is numerically equal to formula mass, but expressed in g/mol Molar mass of H2O = 18.02 g/mol 104 How to Calculate the Molar Mass of Any Substance? To calculate the molar mass of any substance, you must first know its exact chemical formula! The molar mass can be calculated for any substance by summation of the atomic masses (from the periodic table) of all the atoms of elements present this substance’s formula: An element’s molar mass in grams per mole (g/mol) is numerically equal to the element’s atomic mass in atomic mass units (amu). Examples: Calculate the molar mass (g/mol) for: - Molar mass of water (H2O) = (2×1) + (1×16) = 18 g/mol - Molar mass of oxygen (O2) = 2×16 = 32 g/mol - Molar mass of NaCl = (1×23) + (1×35) = 58 g/mol - Molar mass of glucose (C6H12O6) = (12×6) + (12×1) + (16×6) = 180 g/mol 105 B- Molecules, Compounds and Chemical Bonds 3- Chemical Reactions, Chemical equations, Intramolecular Forces, Types of Chemical Bonds, 106 Chemical Reactions A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. The chemical reaction can be described by a chemical equation. The substance (or substances) initially involved in a chemical reaction are called reactants or reagents. The chemical reaction yields one or more products, which usually have properties different from the reactants. A + B AB Reactants Product 107 Chemical Equations Chemical Equation: is a shorthand way of describing a chemical reaction. Provides some basic information about the reaction: – formulas of reactants and products – states of reactants and products – relative numbers of reactant and product molecules that are required – can be used to determine weights of reactants used and products that can be made – Example: CH4(g) + 2 O2(g) CO2(g) + 2 H2O(g) 108 Symbols in Chemical Equations State Symbols (written after the substance’s formula): (g) = gas (↑) (l) = liquid (s) = solid (aq) = aqueous = dissolved in water (ppt) = precipitate (↓) Energy Symbols (Written above the arrow): high-energy visible – Δ = heat light (hv) – hν = light – shock = mechanical – elec = electrical 109 3.9. Balancing Balancing Chemical Chemical Equations Equations To show the reaction obeys the Law of Conservation of Mass, the equation must be balanced: – We adjust the number of molecules so that there are equal numbers of atoms of each element on both sides of the arrow: CH4(g) + 2 O2(g) CO2(g) + 2 H2O(g) 1C + 4H + 4O 1C + 4H + 4O 110 Balancing Chemical Equations: Practice When aluminum metal reacts with oxygen, it produces a white powdery compound, aluminum oxide aluminum(s) + oxygen(g) aluminum oxide(s) ….. Al(s) + ….. O2(g) ….. Al2O3(s) 4 Al(s) + 3 O2(g) 2 Al2O3(s) The coefficients required to balance this equation are: 4, 3, 2, respectively. 111 Assessment 1- Give the coefficients that are necessary to balance each of the following equations: 2- What is the coefficient of H2O when each of the following equations are balanced? 112 Types of Chemical Equations Two types of equations are used to represent chemical reactions: 1- Molecular equations and 2- Ionic equations Example of the molecular equation: NaOH + HCI NaCl + H2O This equation shows that 1 mole of sodium hydroxide will neutralize exactly 1 mole of hydrochloric acid to form exactly 1 mole of sodium chloride and 1 mole of water; in other words, it represents the exact stoichiometry of the reaction. A molecular equation is an equation in which the formulas of the compounds are written as though all substances exist as molecules. 113 Types of Chemical Equations However, there is a better way to show what is happening in this reaction Sodium hydroxide, hydrochloric acid, and sodium chloride are all strong electrolytes and in solution are 100 % ionized. Therefore, a solution of sodium hydroxide contains only Na+ and OH- ions and no NaOH molecules. NaOH Na+ + OH- Similarly, a solution of hydrochloric acid contains only H+ and Cl- ions and no HCI molecules HCI H+ + Cl- Also, a solution of sodium chloride contains Na+ and Cl- ions and no NaCI molecules. NaCI Na+ + Cl- 114 Types of Chemical Equations Water, on the other hand, is an extremely weak electrolyte and exists almost entirely in the form of H2O molecules. So, when a solution of sodium hydroxide is mixed with a solution of hydrochloric acid the expression showing the ionic and molecular species involved would be: Na+ + OH- + H+ + Cl- Na+ + Cl- + H2O It is clear that both Na+ and Cl- do not altered in the reaction. Therefore, the actual change which takes place is expressed by Net Ionic Equation : H+ + OH- H2O 115 How to write Net Ionic Equation? 1) Write the balanced molecular equation. 2) Write the ionic equation showing the strong electrolytes. 3) Determine if there is any precipitate from the solubility rules. 4) Cancel the similar ions on both sides of the ionic equation. 116 How to write Net Ionic Equation? Example 1: Write the net ionic equation of the reaction of sodium hydroxide with hydrochloric acid. The molecular equation: NaOH + HCI NaCl + H2O The ionic equation showing the strong electrolytes: Na+ + OH- + H+ + Cl- Na+ + Cl- + H2O No precipitate is formed; so cancel similar ions: Na+ + OH- + H+ + Cl- Na+ + Cl- + H2O Net ionic equation will be: H+ + OH- H2O 117 How to write Net Ionic Equation? Example 2: Write the net ionic equation of the reaction of a solution of silver nitrate with hydrochloric acid. The molecular equation: AgNO3 + HCI AgCl + HNO3 The ionic equation showing the strong electrolytes: Ag+ + NO3- + H+ + Cl- AgCl + NO3- + H+ Silver chloride (white precipitate) is formed; then cancel the similar ions: Ag+ + NO3- + H+ + Cl- AgCl + NO3- + H+ Net ionic equation will be: Ag+ + Cl- AgCl 118
