Metals, nonmetals, and metalloids. The Periodic Table. Metals, nonmetals, and metalloids. Metals, nonmetals, and metalloids

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1 The Periodic Table Metals, nonmetals, and metalloids A table listing all of the known elements The most important organizing principle in chemistry Properties of metals high luster (shiny) solids at room temperature (except g) good conductors of heat/electricity malleable/ductile (deforms without fracturing) high density high melting point Metals, nonmetals, and metalloids Metals, nonmetals, and metalloids Properties of nonmetals solids at room temperature: carbon, phosphorous, sulfur, selenium, iodine liquids at room temperature: bromine all others are gases at room temperature not lustrous or malleable/ductile poor conductors of heat and electricity low density and melting point Properties of metalloids solids at room temperature properties intermediate between metals and nonmetals

2 Compounds compound -- a combination of two or more elements atoms of the elements in a compound are combined in whole number ratios Examples: Water Elements: hydrogen, oxygen Formula: 2 (two hydrogen atoms for every one oxygen atom) Methanol Elements: carbon, hydrogen, oxygen Formula: C 4 (four hydrogen atoms and one oxygen atom for every one carbon atom) C Molecules molecule -- the smallest individual unit of a compound a combination of two or more atoms from the same or different elements Chemical formulas of compounds The chemical formula of a compound shows which elements it is composed of and how many atoms of each element are present 1. The chemical formula contains the symbols of all the elements in the compound. NaCl 2. Subscripts indicate how many atoms of each element are present. 2 S 4 -- if only one atom of an element is present, the number one (1) is not shown as a subscript water water molecules 3. When the formula contains more than one group of atoms that occurs as a unit, parentheses are placed around the group. -- a subscript indicating how many of the groups are present in the compound appears to the right of the parentheses Example: (hydroxide ion) Na Mg() 2

3 Elements, atoms, compounds, molecules Element or compound? Elements can not be broken down into simpler substances Compounds can be broken down into simpler substances -- i.e., into simpler compounds and/ or elements Atoms are the smallest individual units of elements Examples Molecules are the smallest individual units of compounds -- molecules consist of two or more atoms of the same or different elements sodium (Na) carbon dioxide (C 2 ) Cu copper water ( 2 ) Mg magnesium Cl Cl chlorine ( Cl 2 ) sodium chloride (NaCl) mercury (g) Elements that exist as diatomic molecules There are seven elements that exist as diatomic molecules -- i.e., molecules that contain exactly two atoms Pure substances and mixtures substance -- a specific type of matter with a definite, fixed composition -- i.e., either elements or compounds mixture -- material containing two or more substances in variable proportions that are physically mixed but not chemically combined Element Symbol Formula ydrogen 2 Nitrogen N N 2 xygen 2 Fluorine F F 2 Chlorine Cl Cl 2 As free elements (i.e., when they are not part of a compound) these elements are always encountered as diatomic molecules Differences between compounds and mixtures Composition Separation of components Compounds Composed of two or more elements in definite, fixed proportions nly by chemical changes Mixtures May be composed of elements, compounds, or both in variable proportions By physical or mechanical means Bromine Br Br 2 Iodine I I 2 diatomic hydrogen gas molecule Identification of components A compound does not resemble the components from which it is formed Components do not lose their identity

4 Compounds vs. mixtures Types of mixtures Mixture of iron and sulfur Consists of Fe and S, but no definite formula Contains Fe and S in any proportion by mass Fe and S can be separated by physical means Compound of iron and sulfur FeS (iron sulfide) 63.5% Fe and 36.5% S by mass Fe and S can be separated only by chemical change omogeneous mixtures -- uniform in appearance -- has the same properties throughout -- solutions are homogeneous mixtures Examples: Fruit punch (water, sugar, red food coloring) Air (nitrogen, oxygen, C 2, argon, other gases) eterogeneous mixtures -- consists of visibly different substances or phases Examples: Trail mix (peanuts, cashews, M&Ms) Beach sand (bits of rocks, minerals, shells, coral) Fizzy mineral water (liquid, gas bubbles) Pure substances and mixtures Element, compound or mixture? Pure substances Fixed composition Mixtures Variable composition Not chemically combined Components can be separated by physical means Baking soda (sodium bicarbonate -- NaC 3 ) Salt and sugar combined in a bowl Salt (NaCl) crystals dissolved in water Elements nly one type of atom Compounds Two or more different types of atoms (elements) omogeneous uniform appearance and properties solutions eterogeneous visibly different substances or phases Nitrogen gas Rust (iron oxide -- Fe 2 3 ) Coffee Liquid ammonia (N 3 )

5 Physical and chemical changes Matter can undergo two types of changes -- physical and chemical Physical changes are changes in the physical properties of a substance (e.g., size, shape, density) or changes in the state of matter (solid, liquid, gas) without an accompanying change in chemical composition Examples: Melting ice (change from solid to liquid state) Boiling methanol (change from liquid to vapor state) eating water (increase in volume, decrease in density) ammering a gold nugget into a thin sheet of foil (change in size, shape) Physical and chemical changes Matter can undergo two types of changes -- physical and chemical Chemical changes result in the formation of new substances that have different properties and composition than the starting materials Examples: Adding vinegar to baking soda (fizzing bubbles indicate acid-base neutralization reaction) eating a copper wire to form black residue on surface (conversion of metallic copper to copper (II) oxide) Note: eating a platinum wire does not result in the formation of a residue on the wire (physical changes, but no chemical changes) Using electricity to split water into hydrogen and oxygen gas (electrolysis) No new substances are formed in physical changes Example: Thermite reaction Chemical reactions The term chemical reaction means the same thing as chemical change chemical reaction -- a process in which atoms, molecules and/or ions rearrange to form new substances substances are consumed and new substances are formed chemical bonds are broken and new bonds are formed Thermite is a mixture of aluminum and iron oxide powder the aluminum and iron oxide react to form iron and aluminum oxide aluminum + iron (III) oxide iron + aluminum oxide This reaction also generates a LARGE amount of heat Chemical reactions chemical equation -- shorthand expression for a chemical reaction aluminum + iron (III) oxide 2 Al + Fe Fe + Al 2 3 reactants iron + aluminum oxide products reactant -- a starting substance that undergoes change during a chemical reaction product -- a substance formed as a result of a chemical reaction Reactants and products are separated by an arrow indicating the direction of the reaction

6 Physical quantities (measurements) A measurement of a physical property always consists of a numerical value together with a unit of that measurement The Metric System A decimal system (i.e., based on powers of 10) of units for measurements of mass, length, time, and other physical quantities Example: Length -- standard unit is the meter ( 1 m! 3.28 ft ) Examples: 12.5 meters 70.0 kilograms 89 F numerical value unit numerical value unit numerical value unit megameter (Mm) 10 6 m kilometer (km) 10 3 m hectometer (hm) 10 2 m dekameter (dam) 10 1 m meter (m) 10 0 m ( = 1 m ) decimeter (dm) 10-1 m centimeter (cm) 10-2 m millimeter (mm) 10-3 m micrometer (!m) 10-6 m nanometer (nm) 10-9 m Mass mass -- the amount of matter that an object possesses standard metric system unit (SI unit) is the kilogram (kg) 1 kg of mass is contained in an object that weighs 2.2 lbs (Note: mass and weight are not the same thing -- this will be explained in a minute) 1 kg = 1000 g 1 g = 1000 mg 1 kg = 10 6 mg 1 mg = g = 10-6 kg 1 kg mass -- amount of matter contained by object Mass and Weight 1 kg 2.2 lbs weight -- amount of force exerted on an object due to Earth s gravitational pull F = mg F = (1.0 kg)(9.8 m/s 2 ) F = 9.8 kg m/s 2 = 9.8 Newtons 9.8 N = 2.2 lbs g = 9.8 m / s 2

7 Earth s surface Mass and Weight The mass of an object is constant The weight of an object can change uter space Volume volume -- the amount of space occupied by matter standard metric system unit (SI unit) is the cubic meter (m 3 ) Commonly used units include the liter (L) and milliliter (ml) mass = 70 kg g = 9.8 m/s 2 mass = 70 kg g " 0 m/s 2 1 m 3 = 1000 L = 10 6 ml 1 L = 1000 ml 1 ml is also equivalent to one cubic centimeter (cm 3 or cc) 154 lbs weight! 0 lbs weight Volume Temperature Temperature is commonly measured on three different scales: Fahrenheit, Celsius, and Kelvin (the SI unit of temperature is Kelvin) 1 m 3 m 2 m 0 C = K = 32 F 100 C = K = 212 F For a rectangular solid: volume = length x width x height volume = 3 m x 2 m x 1 m = 6 m 3 volume " 100 ml T(K) = T( C) T( F) = [ 1.8 x T( C) ] + 32 T( C) = [ T( F) - 32 ] / 1.8

8 Temperature Example: What is 86 F in degrees centigrade ( C)? T( C) = [ T( F) - 32 ] / 1.8 T( C) = [ ] / 1.8 T( C) = 54 / 1.8 T( C) = 30. C Example: What is 30.0 C in degrees Kelvin (K)? T(K) = T( C) T(K) = T(K) = K Review: Scientific Notation scientific notation -- expressing a number as a power of 10 (a convenient way of writing very large and very small numbers) To put a number in scientific notation: move the decimal point left or right until there is only one digit to the left of the decimal point -- this is the base number count the number of places you had to move the decimal point -- this is the exponent for the power of 10!positive if the decimal point moved to the left!negative if it moved to the right Examples: 1000 = ,052 = x = 2.5 x = 5 x 10-2 Review: Scientific Notation Significant figures scientific notation -- expressing a number as a power of 10 (a convenient way of writing very large and very small numbers) Avogadro number (number of atoms or molecules in one mol) 602,200,000,000,000,000,000,000 atoms/mol Scientific notation: x atoms/mol Numbers obtained from measurements are never exact values there is always some degree of uncertainty due to limitations of the measuring instrument and skill of the analyst the numerical value recorded for a measurement should give an indication of its precision (reliability) significant figures -- the number of digits in a measured value that are known precisely, plus one estimated digit ne nanometer (1 billionth of a meter) meters Scientific notation: 1.0 x 10-9 meters igher level of precision in making the measurement = More significant figures

9 Significant figures Significant figures The number of significant figures in a measured value reflects the level of precision associated with the method of measurement significant figures -- the number of digits in a measured value that are known precisely, plus one estimated digit What is the length of the metal bar? one significant figure (0 precise + 1 estimated) 2? ? g two significant figures (1 precise + 1 estimated) 1.61? three significant figures (2 precise + 1 estimated) g Top-Loading Balance Capacity: 1500 g Precision: ± 0.01 g Sample Mass: 3.12 g Significant figures Exact numbers 52.6 ml What is the volume of water in the graduated cylinder? Exact numbers have no uncertainty -- and therefore have an infinite number of significant figures 3 sig figs ow many significant figures in this measurement? Semi-Micro Balance Capacity: 10 g Precision: ± g Sample Mass: g Exact numbers result from simple counting operations people 5 samples Defined numbers are exact number of inches in one foot = 12 inches 53 ml ml number of minutes in one hour = 60 minutes

10 omework Chapter 1 Problems: 1.18, 1.24, 1.25, 1.29, 1.31, 1.37, 1.45, 1.50, 1.56, 1.60 Chapter 2 Problems: 2.26, 2.29, 2.34, 2.44, 2.45