Atoms, Molecules, and the States of Matter Chapter 1

Universe Classified Matter is the part of the universe that has mass and volume Energy is the part of the universe that has the ability to do work Chemistry is the study of matter The properties of different types of matter The way matter behaves when influenced by other matter and/or energy 3

Elements and Compounds Substances which can not be broken down into simpler substances by chemical reactions are called elements Most substances are chemical combinations of elements. These are called compounds. Compounds are made of elements Compounds can be broken down into elements Properties of the compound not related to the properties of the elements that compose it Same chemical composition at all times 11

Elements Over 112 known, of which 88 are found in nature others are man-made Abundance is the percentage found in nature oxygen most abundant element (by mass) on earth and in the human body the abundance and form of an element varies in different parts of the environment Each element has a unique symbol The symbol of an element may be one letter or two if two letters, the second is lower case 2

The periodic table

Distribution (Mass Percent) of the 18 Most Abundant Elements in the Earth's Crust, Oceans, and Atmosphere

Abundance of elements in the human body

Metallic Character Metals Metalloids Nonmetals malleable & ductile shiny, lustrous conduct heat and electricity most oxides basic and ionic form cations in solution lose electrons in reactions - oxidized Metalloids Also known as semi-metals Show some metal and some nonmetal properties Nonmetals brittle in solid state dull electrical and thermal insulators most oxides are acidic and molecular form anions and polyatomic anions gain electrons in reactions - reduced 22

The classification of elements as metals, nonmetals, and metalloids

Dalton’s Atomic Theory Elements are composed of atoms tiny, hard, unbreakable, spheres All atoms of a given element are identical all carbon atoms have the same chemical and physical properties Atoms of a given element are different from those of any other element carbon atoms have different chemical and physical properties than sulfur atoms 3

Dalton’s Atomic Theory Atoms of one element combine with atoms of other elements to form compounds. Atoms are indivisible in a chemical process. all atoms present at beginning are present at the end atoms are not created or destroyed, just rearranged atoms of one element cannot change into atoms of another element 4

Elements and Compounds Substances which can not be broken down into simpler substances by chemical reactions are called elements Most substances are chemical combinations of elements. These are called compounds. Compounds are made of elements Compounds can be broken down into elements Properties of the compound not related to the properties of the elements that compose it Same chemical composition at all times

Formulas Describe Compounds a compound is a distinct substance that is composed of atoms of two or more elements describe the compound by describing the number and type of each atom in the simplest unit of the compound molecules or ions each element represented by its letter symbol the number of atoms of each element is written to the right of the element as a subscript if there is only one atom, the 1 subscript is not written 6

Dalton pictured compounds as collections of atmosphere NO, NO2, and N2O are represented

Classification of Matter Homogeneous = uniform throughout, appears to be one thing pure substances solutions (homogeneous mixtures) Heterogeneous = non-uniform, contains regions with different properties than other regions 12

Pure Substances vs. Mixtures All samples have the same physical and chemical properties Constant Composition  all samples have the same composition Homogeneous Separate into components based on chemical properties Mixtures Different samples may show different properties Variable composition Homogeneous or Heterogeneous Separate into components based on physical properties All mixtures are made of pure substances 13

Table salt is stirred into water (left), forming a homogeneous mixture called a solution (right)

Sand and water do not mix to form a uniform mixture

Identify Each of the following as a Pure Substance, Homogeneous Mixture or Heterogeneous Mixture Gasoline a homogenous mixture A stream with gravel on the bottom a heterogeneous mixture Copper metal A pure substance (all elements are pure substances) 15

Colloids and Emulsions Colloid = mixture of one finely divided material dispersed in another Emulsions = colloids where both compounds are liquids; often commercially useful Ice cream, mayonnaise Emulsifying agent = helps keep two substances from separating (egg yolk keeps water and oil separate in mayonnaise)

The organization of matter

States of Matter solid, liquid, gas 7

The three states of water

Changes in Matter Physical Changes are changes to matter that do not result in a change of the fundamental components that make that substance State Changes – boiling, melting, condensing Chemical Changes involve a change in the fundamental components of the substance Produce a new substance Chemical reaction Reactants  Products 8

Classify Each of the following as Physical or Chemical Changes Iron is melted. Physical change – describes a state change, but the material is still iron Iron combines with oxygen to form rust. Chemical change – describes how iron and oxygen react to make a new substance, rust Sugar ferments to form ethyl alcohol. Chemical change – describes how sugar forms a new substance (ethyl alcohol) 10

Kinetic - Molecular Theory The properties of solids, liquids and gases can be explained based on the speed of the molecules and the attractive forces between molecules In solids, the molecules have no translational freedom, they are held in place by strong attractive forces May only vibrate 18

Solids amorphous solids crystalline solids show no definite structure therefore strengths of intermolecular forces vary over the structure glass, plastic, rubber tend to soften and melt over a temperature range crystalline solids orderly, repeating, 3-dimensional pattern pattern = crystal lattice melt at one specific temperature 5

The arrangement of sodium ions (Na+) and chloride ions (Cl-) in the sodium chloride, NaCl.

Kinetic - Molecular Theory In liquids, the molecules have some translational freedom, but not enough to escape their attraction for neighboring molecules They can slide past one another, rotate as well as vibrate In gases, the molecules have “complete” freedom from each other, they have enough energy to overcome “all” attractive forces 19

Describing a Gas Gases are composed of tiny particles The particles are small compared to the average space between them Assume the molecules do not have volume Molecules constantly and rapidly moving in a straight line until they bump into each other or the wall Average kinetic energy proportional to the temperature Results in gas pressure Assumed that the gas molecules attraction for each other is negligible 20

Gas Properties Explained Gases have indefinite shape and volume because the freedom of the molecules allows them to move and fill the container they’re in Gases are compressible and have low density because of the large spaces between the molecules 21

Gas Pressure Pressure = total force applied to a certain area larger force = larger pressure smaller area = larger pressure Gas pressure caused by gas molecules colliding with container or surface More forceful collisions or more frequent collisions mean higher gas pressure 3

The pressure exerted by the gases in the atmosphere can demonstrated by boiling water in a can

Liquid Crystals State of matter intermediate to solid and liquid Only occurs for a few compounds, usually for molecules that are long and rod-shaped. The ordered arrangement can be re-ordered by changing the liquid crystal’s environment Numbers on a digital watch appear as a liquid crystal realigns due to electrical charge and becomes opaque

Metallic Mixtures Alloys are mixtures of elements that show metallic properties Substitutional Alloys have some host metal atoms replaced by metal atoms of similar size Brass = Copper with Zinc substituted Interstitial Alloys have small atoms occupying some of the holes in the crystal lattice of the host metal Steel = Iron with Carbon added 24

Two types of alloys