Reading Essentials for Biology Glencoe (794133), страница 16
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A molecule has no charge, positiveor negative.How do covalent bonds form?pⴙ8pⴙ8n 0Watermolecule5. Compare What does acovalent bond do thatan ionic bond does not?(Circle your choice.)a. shares electronsb. shares neutronsc. shares atoms56Chapter 6Most compounds in organisms have covalent bonds. Water is agreat example. In a molecule of water, there are two hydrogenatoms and one oxygen atom. Each hydrogen atom shares its oneelectron. The oxygen atom shares the six electrons it has in itsouter energy level.
By sharing eight electrons, all three atomsbecome stable.How do ionic bonds form?Not all atoms bond together by sharing electrons. A sodiumatom and a chlorine atom bond in another way to make table salt.A sodium atom has 11 electrons. This means the outer energylevel has only one electron (2 in first level, 8 in second level, 1 inthird level).
A chlorine atom has 17 electrons. This means thatthere are seven electrons in a chlorine atom’s outer level (2 in firstlevel, 8 in second level, 7 in third level). When sodium and chlorinebond together, the sodium atom loses one electron to the chlorineatom. The chlorine atom gains this electron. When an atom gainsor loses electrons, it becomes electrically charged. It is then calledan ion. An ion is a positively or negatively charged atom.As a result of bonding, the sodium ion now has eight electronsin its outer energy level. This makes the sodium ion stable, butgives it a positive charge, because it now has more protons thanelectrons.
The chloride ion now also has eight electrons in itsouter level. It is stable but has a negative charge since it now hasmore electrons than protons. These opposite charges attract thesodium ion to the chloride ion. This attractive force between twoions of opposite charge is known as an ionic bond. An ionicbond, then, is what bonds sodium and chlorine together to maketable salt.READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.pⴙNameDateClassSection6.1Atoms and Their Interactions, continuedIonic bond+NaClCl atom: 17 p17 eNa atom: 11 p11eSodium atomChlorine atomNaClNaClCl ion: 17 p18 eNa ion: 11 p10eSodiumionChlorideionNaClChemical ReactionsCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.The forming or breaking of bonds is what causes substancesto combine in different ways to make other substances.
Chemical reactions take place when bonds are formed and broken. Inorganisms, chemical reactions occur inside cells. All of the chemical reactions that take place within an organism are known asthat organism’s metabolism. These reactions break downand build substances that are important for the organism tofunction properly.How do you write chemical equations?Scientists describe what happens in chemical reactions by usingchemical equations (i KWA zhunz).
These are a combination ofelement symbols and numbers. They explain how many substances are involved in a reaction. They also show how these substances join together or come apart. For example, hydrogen andoxygen bond together, or react, to form water. Here is the equation that describes this:2H2 + O2 → 2H2OH is the symbol for hydrogen.
O is the symbol for oxygen. But thenumbers are important, too. The subscript numbers (the smallernumbers after a symbol) show how many atoms of each elementare in a substance. The number before a substance tells how manymolecules are in the substance. If there is no number before asubstance, this means that there is only one molecule of it.So, in the sample equation, 2H2 means that there are two molecules of hydrogen.
Each molecule is made of two hydrogen atoms.O2 means that there is one molecule of oxygen, and the moleculeis made up of two oxygen atoms.READING ESSENTIALS6. What causes substancesto combine in differentways to make othersubstances?________________________________________________________________________7. Explain the meaning ofeach of the followingsymbols in a chemicalequation.Number before anelement:________________________________________________Subscript number afteran element:________________________________________________Chapter 657NameDateClassSectionAtoms and Their Interactions, continued8. Analyze Pouring milkover cereal creates a solution. (Circle your choice.Then, on the lines provided, explain youranswer.)a.
Trueb. False________________________________________________________________________________________________Since hydrogen and oxygen are the substances that are involvedin the reaction, they are called reactants. Reactants always appearbefore the arrow in a chemical equation. The result of a reactionis known as a product. It always comes after the arrow in theequation.
The product in this reaction is water. 2H2O meansthat there are two molecules of water that result from this reaction. Each molecule is made of two hydrogen atoms and oneoxygen atom.It is important to understand that in chemical reactions, atomsare never destroyed or created.
They are simply rearranged.Equations show this by having the same number of atoms of eachelement before and after the arrow.Mixtures and SolutionsMixtures When elements combine chemically to form a compound, the elements no longer have their original properties.Sometimes, though, substances mix together but do not chemically combine. This makes a mixture. A mixture is a combinationof substances in which the individual substances keep their ownproperties. Stirring sand and sugar together in a bowl, for example, makes a mixture. Neither the sand nor the sugar changes.They do not combine chemically.Solutions A solution is a special type of mixture.
In a solution,one or more substances (solutes) dissolve in another substance(solvent). Equal amounts of the solute are then found throughoutthe solvent. For example, stirring a pack of powdered drink mix insome water makes a solution. The powder in the drink mix dissolves and is the solute. The water is the solvent. If you want thedrink to taste right, you must know how much solute (drink mixpowder) to dissolve in your solvent (water).
The measure of theamount of solute dissolved in a solvent is called concentration.The more solute that is dissolved in a given amount of solvent,the greater the concentration.Acids and Bases Chemical reactions take place only when conditions are just right. A reaction might need a certain temperatureor a certain amount of energy. It might depend on the right concentration of a substance in a solution. Chemical reactions inorganisms also depend on the pH of the environment inside theorganism.
The pH measures how acidic or basic a solution is. Ascale from below 0 to above 14 is used to measure pH. Substanceswith a pH below 7 are acidic. An acid is any substance that formshydrogen ions (H+) in water. (Remember, ions have either a58Chapter 6READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.6.1NameDateClassSection6.1Atoms and Their Interactions, continuedHouseholdammoniapH 11MilkpH 6TomatopH 4AntacidpH 10LemonpH 201DraincleanerpH 13EggpH 8234567891011121314NeutralCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.More acidicMore basicpositive or negative charge. That is what the + or – means after anelement’s symbol.) For example, when hydrogen chloride (HCl) isadded to water, hydrogen ions (H+) and chloride ions (Cl – ) areformed. That is why hydrogen chloride in a solution with wateris called hydrochloric acid.
This acidic solution contains many,many hydrogen ions (H+). The solution’s pH is below 7.Substances with a pH above 7 are basic. A base is any substance that forms hydroxide ions (OH – ) in water. For example, ifsodium hydroxide (NaOH) is dissolved in water, it forms sodiumions (Na+) and hydroxide ions (OH – ). This basic solution contains many, many hydroxide ions (OH – ) and has a pH above 7.If a substance is not acidic or basic, it is neutral. Neutral substances have a pH of 7. The figure above shows common acidsand bases.9.
What is the pH of a neutral substance?________________________________________________◗ After You ReadMini Glossaryacid: any substance that forms hydrogen ions(H+) in water. Acids have a pH below 7.ion: atom or group of atoms that gain or loseelectrons; has an electrical chargeatom: smallest particle of an element; basicbuilding block of all matterionic bond: chemical bond formed by theattractive forces between two ions of opposite chargebase: any substance that forms hydroxide ions(OH– ) in water.
Bases have a pH above 7.compound: substance composed of atoms oftwo or more elements that are chemically combinedisotopes: atoms of the same element that havedifferent numbers of neutrons in the nucleusmetabolism: all of the chemical reactions thatoccur within an organismcovalent (koh VAY lunt) bond: chemical bondformed when two atoms share electronsmixture: combination of substances in which individual components keep their own propertieselements: substances that cannot be brokendown into simpler chemical substancesmolecule: group of atoms held together by covalent bonds; has no overall chargeREADING ESSENTIALSChapter 659NameDateClassSection6.1Atoms and Their Interactions, continuednucleus: positively charged center of an atommade of neutrons and positively chargedprotons, and surrounded by negativelycharged electronssolution: mixture in which one or more substances (solutes) are distributed evenly inanother substance (solvent)pH: measure of how acidic or basic a solution is;the scale ranges from below 0 to above 14;solutions with a pH above 7 are basic and apH below 7 are acidic1.
Review the terms and their definitions in the Mini Glossary. Then choose two of the termsthat are related. Write a sentence explaining how the terms are related.____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________2.
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