CHEM 1305: Introductory Chemistry

Transcription

1 CHEM 1305: Introductory Chemistry Properties of Matter From Chapter 2 and 3 Textbook Introductory Chemistry: Concepts and Critical Thinking Seventh Edition by Charles H. Corwin

2 Physical States of Matter Matter is defined as a substance that has mass and occupies volume It exists in one of three physical states: Solid particles are tightly packed, held in rigid positions Liquid particles are loosely packed, free to move around Gas particles are widely spaced apart and uniformly distributed 2

3 Physical States of Matter Every substance can exist as a solid, liquid, or gas With increasing temperatures: Solid ice melts to liquid water at 0 C Liquid water vaporizes to steam at 100 C With decreasing temperatures: Steam condenses back to water at 100 C Water freezes back to ice at 0 C 3

4 Physical States of Matter The direct change of state from a solid to a gas is called a sublimation Dry ice sublimes directly from a solid to a gas (carbon dioxide) The direct change of state from a gas to a solid is called a deposition Opening a freezer door causes deposition of frost inside without a trace of liquid water 4

5 Change of Physical State State the term that applies to each of the following physical changes Snow changes from a solid to a liquid melting Gasoline changes from a liquid to a gas vaporizing Dry ice changes from a solid to a gas sublimation A refrigerant changes from a gas to a liquid condensation Water changes from a liquid to a solid freezing Iodine vapor changes from a gas to a solid deposition Gas Liquid Solid 5

6 Temperature Temperature is the average kinetic energy of individual particles in motion, and it is measured with a thermometer Three temperature scales: Fahrenheit degree (symbol F) Celsius degree (symbol C) Kelvin unit (symbol K) Lowest possible temperature is C, 0 K No highest temperature, but the sun s interior is ~10,000,000K 6

7 Temperature Conversions 180 Fahrenheit units are equivalent to 100 Celsius units (212 F - 32 F) The difference between the freezing point from F to C is 32 Celsius units are equivalent to Kelvin units, but the Kelvin scale is 273 units above the Celsius scale C = K 100 C ( F - 32 F) = C 180 F 180 F C + 32 F = F 100 C 7

8 Temperature Conversions Normal body temperature is 98.6 F. What is normal body temperature in degrees Celsius? 100 C (98.6 F - 32 F) = C 180 F 100 C 66.6 F = 37.0 C 180 F The temperature in Celsius of liquid nitrogen is -196 C, what is the Kelvin temperature? -196 C = 77 K 8

9 Elements, Compounds, and Mixtures A sample of matter may be a mixture or it may be a pure substance Mixtures are composed of more than one substance and can be physically separated into its component substances A heterogeneous mixture DOES NOT have uniform properties throughout A homogeneous mixture DOES have uniform properties throughout Sand in water is a heterogeneous mixture Table salt in water is a homogeneous mixture 9

10 Elements, Compounds, and Mixtures A homogeneous mixture of two or more metals is known as an alloy 10K, 14K, 18K jewelry may contain varying amounts of gold, silver and copper Pure substances are composed of only one substance and cannot be physically separated A substance has definite composition and constant properties A compound CAN be broken down into elements by an ordinary chemical reaction An element CANNOT be broken down further by a chemical reaction Sugar is a compound Mercury is an element 10

11 Classification of Matter 11

12 Element, Compound, or Mixture Classify each of the following samples as an element, compound, homogeneous mixture, or heterogeneous mixture a) Copper metal element cannot be broken down by a chemical change b) Copper oxide compound copper which has reacted with oxygen c) Vinaigrette salad dressing d) Apple juice homogeneous mixture e) Mercury liquid element cannot be broken down by a chemical change f) Mercury oxide compound when heated, gives mercury and oxygen gas g) Dental alloy homogeneous composed of mercury mixture and silver h) Chicken noodle soup heterogeneous mixture heterogeneous mixture 12

13 Names and Symbols of the Elements There are over 100 elements, 81 of which are stable and occur naturally Only 10 elements account for 95% of the mass of Earth s crust, water, and atmosphere Oxygen is the most abundant element, it constitutes 21% of the atmosphere and combines with hydrogen to form water 13

14 Names and Symbols of the Elements The elements oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus account for over 99% of the mass of the human body Other trace elements are also essential to life iron is necessary to bind oxygen to hemoglobin in the blood 14

15 Names and Symbols of the Elements Each element has a unique name Hydrogen is derived from the Greek word hydro, meaning water former Carbon is derived from the Latin word carbo, meaning coal Calcium is derived from the Latin word calcis, meaning lime (as in limestone) Scandium is named for Scandinavia Curium is named for Marie Curie In 1803, English chemist John Dalton ( ) proposed that elements are composed of indivisible, spherical particles each of these particles are referred to as an atom, from the Greek word atomos, meaning indivisible The name of each element is abbreviated using a chemical symbol 15

16 Names and Symbols of the Elements Chemical symbols are one or two letters long (capitalize only first letter), and are generally derived from the name of the element Two letters are used if the element starts with the same letter: C is for carbon Co for cobalt (not CO that is carbon monoxide) Cl for chlorine Some chemical symbols are derived from original Latin or Greek names: Pb for lead, from plumbum Hg for mercury, from hydrargyro Au for gold, from aurum Cu for copper, cuprum Fe for iron, from ferrum K for potassium, from kalium Na for sodium, natrium Sb for antimony, from stibium Sn for tin, from stannum Ag for silver, argentum 16

17 Metals, Nonmetals, and Semimetals Three classes of elements: metals, nonmetals, and semimetals A malleable metal can be hammered into a thin sheet of foil A ductile metal can be drawn into a fine wire 17

18 Metals, Nonmetals, and Semimetals Metals high density, high melting point, good conductor of heat and electricity, bright metallic luster, malleable and ductile: aluminum, copper, silver Nonmetals low density, low melting point, poor conductor of heat and electricity, dull appearance, crush to a powder if hammered: phosphorus, sulfur, carbon Semimetals midway between metals and nonmetals: silicon, arsenic, boron 18

19 Periodic Table of the Elements Each element is assigned a number, known as the atomic number and elements are arranged by that number in the periodic table 19

20 Physical States of the Elements All metals and semimetals are solid, except for mercury (Hg) 5 nonmetals are solid, 1 is liquid, 11 are gases 20

21 Compounds and Chemical Formulas Law of definite composition compounds always contain the same elements in a constant proportion by mass Water is always 11.2% hydrogen and 88.8% oxygen, no matter if it is solid, liquid or gas, or where it comes from Sodium chloride is always 39.3% sodium and 60.7% chlorine Most elements occur naturally as a collection of individual atoms A few nonmetal elements, such as hydrogen and oxygen, occur naturally as two or more atoms of the element in a single unit a molecule Hydrogen exists as H 2 Oxygen exists as O 2 21

22 Chemical Formulas In a molecule or compound, a chemical formula expresses the number of atoms of each element present Number of atoms is indicated with a subscript, unless the number is 1 Water contains two hydrogen atoms and one oxygen atom Chemical formula is written as H 2 O Sulfuric acid has two hydrogen atoms, one sulfur atom, and four oxygen atoms Chemical formula is written as H 2 SO 4 22

23 Composition of Chemical Formulas State the total number of atoms in a molecule of vitamin B 3 : C 6 H 6 N 2 O There are 15 total atoms: 6 carbon atoms, 6 hydrogen atoms, 2 nitrogen atoms, and 1 oxygen atom Write the chemical formula for vitamin B 6, which is composed of 8 carbon atoms, 11 hydrogen atoms, 1 nitrogen atom, and 3 oxygen atoms C 8 H 11 NO 3 (total 23 atoms) Write the molecular formula for vitamin C, based on the model shown (black = carbon, white = hydrogen, and red = oxygen) 6 carbon atoms, 8 hydrogen atoms, 6 oxygen atoms to give C 6 H 8 O 6 23

24 Physical and Chemical Properties The properties of a compound are never the same as its constituent elements NaCl A physical property refers to characteristics of a pure substance that we can observe without changing the composition of that substance Appearance, melting and boiling points, density, heat, solubility, electrical conductivity, etc. A chemical property of a pure substance describes its chemical reactions with other substances For sodium its reaction with oxygen to form sodium oxide, and its reaction with water to form hydrogen gas and sodium hydroxide 24

25 Physical and Chemical Changes In a physical change, the chemical composition of the sample does not change ice melts to water (still H 2 O), alcohol vaporizes (still C 2 H 5 OH) In a chemical change, there is a chemical reaction, and a new substance is formed Possible observations: Color change Odor forms Bubbles are seen Gas is released Light energy released Heat energy released 25

26 Physical and Chemical Changes Classify each of the following samples as physical or chemical change a) Touching a lit candle to hydrogen soap bubbles gives an explosion b) Heating water in a flask produces moisture on the glass c) Combining two colorless solutions gives a yellow solid d) Pouring vinegar on baking soda produces gas bubbles e) Freezing water in a freezer makes cubes of ice f) Adding silver nitrate to tap water gives a cloudy solution g) Burning sulfur gives a light blue flame h) Grinding aspirin tablets produces a powder 26

27 Physical and Chemical Changes Classify each of the following samples as physical or chemical change a) chemical change b) physical change c) chemical change d) chemical change e) physical change f) chemical change g) chemical change h) physical change 27

28 Conservation of Mass Law In the late 1700s, French chemist Antoine Lavoisier found that the mass of reactants before a chemical change was always equal to the mass of products after the change law of conservation of mass Hydrogen and oxygen always combine in the same ratio by mass to form water 1.0 g hydrogen g oxygen = 9.0 g water Passing an electric current through water produces hydrogen and oxygen 45.0 g water g hydrogen = 40.0 g oxygen The conservation of mass law was used, historically, to determine the formulas of compounds and to develop the first periodic table of elements 28

29 Conservation of Mass Law In an experiment, g of magnesium metal was ignited and burned with oxygen in the air. If g of white magnesium oxide powder, MgO, was collected, what was the mass of oxygen gas that reacted? g Mg + mass of O = g MgO mass of O = g If g of zinc metal reacts with of yellow powdered sulfur, what is the mass of the zinc sulfide produced? g Zn g S = mass of ZnS mass of ZnS = g Heating g copper metal with yellow sulfur produces g of black copper sulfide. What is the mass of sulfur that reacted with the copper metal? g Cu + mass of S = g Cu 2 S mass of S = g 29