chapter 2 review big ideas you should know. concept 2.1: matter consists of chemical elements in...

Chapter 2 ReviewChapter 2 Review

Big Ideas You Should KnowBig Ideas You Should Know

Concept 2.1: Matter consists of chemical Concept 2.1: Matter consists of chemical elements in pure form and in elements in pure form and in

combinations called compoundscombinations called compounds• Organisms are composed of Organisms are composed of mattermatter• Matter is anything that takes up space Matter is anything that takes up space

and has massand has mass

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Table 2-1Table 2-1

Concept 2.2: An elementConcept 2.2: An element’’s propertiess propertiesdepend on the structure of its atomsdepend on the structure of its atoms

Each element consists of unique Each element consists of unique atomsatoms An atom is the smallest unit of matter that An atom is the smallest unit of matter that

still retains the properties of an elementstill retains the properties of an element


Valence electrons Valence electrons are those in the are those in the outermost shell, or outermost shell, or valence shellvalence shell

The chemical behavior of an atom is The chemical behavior of an atom is mostly determined by the valence mostly determined by the valence electronselectrons

Elements with a full valence shell are Elements with a full valence shell are chemically chemically inertinert


Fig. 2-UN3Fig. 2-UN3

Nucleus

Protons (+ charge)determine element

Neutrons (no charge)determine isotope Atom

Electrons (– charge) form negative cloudand determinechemical behavior

Concept 2.3: The formation and function Concept 2.3: The formation and function of molecules depend on chemical bonding of molecules depend on chemical bonding

between atomsbetween atoms

• Atoms with incomplete valence shells can share or transfer valence electrons with certain other atoms

• These interactions usually result in atoms staying close together, held by attractions called chemical bonds


Covalent BondsCovalent Bonds

A A covalent bond covalent bond is the sharing of a is the sharing of a pair of valence electrons by two atomspair of valence electrons by two atoms

In a covalent bond, the shared In a covalent bond, the shared electrons count as part of each atomelectrons count as part of each atom ’’s s valence shellvalence shell


Fig. 2-11Fig. 2-11 Hydrogenatoms (2 H)

Hydrogenmolecule (H2)

In a In a nonpolar covalent bondnonpolar covalent bond, the , the atoms share the electron equallyatoms share the electron equally

In a In a polar covalent bondpolar covalent bond, one , one atom is more electronegative, and atom is more electronegative, and the atoms do not share the the atoms do not share the electron equallyelectron equally

Unequal sharing of electrons Unequal sharing of electrons causes a partial positive or causes a partial positive or negative charge for each atom or negative charge for each atom or moleculemolecule


Fig. 2-13Fig. 2-13

–

+ +H H

O

H2O

Ionic BondsIonic Bonds

Atoms sometimes strip electrons Atoms sometimes strip electrons from their bonding partnersfrom their bonding partners

An example is the transfer of an An example is the transfer of an electron from sodium to chlorineelectron from sodium to chlorine

After the transfer of an electron, After the transfer of an electron, both atoms have chargesboth atoms have charges

A charged atom (or molecule) is A charged atom (or molecule) is called an called an ionion



Ionic bond

Electrontransferforms ions

NaSodium atom

ClChlorine atom

Na+

Sodium ion(a cation)

Cl–

Chloride ion(an anion)

Hydrogen BondsHydrogen Bonds

A A hydrogen bond hydrogen bond forms when a forms when a hydrogen atom covalently hydrogen atom covalently bonded to one electronegative bonded to one electronegative atom is also attracted to another atom is also attracted to another electronegative atomelectronegative atom

In living cells, the In living cells, the electronegative partners are electronegative partners are usually oxygen or nitrogen usually oxygen or nitrogen atomsatoms


Molecular Shape and Molecular Shape and FunctionFunction

A moleculeA molecule’’s shape is usually very s shape is usually very important to its functionimportant to its function

A moleculeA molecule’’s shape is determined by s shape is determined by the positions of its atomsthe positions of its atoms’’ valence valence orbitalsorbitals

In a covalent bond, the In a covalent bond, the ss and and pp orbitals may hybridize, creating orbitals may hybridize, creating specific molecular shapesspecific molecular shapes


Biological molecules recognize and Biological molecules recognize and interact with each other with a interact with each other with a specificity based on molecular shapespecificity based on molecular shape

Molecules with similar shapes can Molecules with similar shapes can have similar biological effectshave similar biological effects


Concept 2.4: Chemical reactions make Concept 2.4: Chemical reactions make and break chemical bondsand break chemical bonds

Chemical reactions Chemical reactions are the are the making and breaking of chemical making and breaking of chemical bondsbonds

The starting molecules of a The starting molecules of a chemical reaction are called chemical reaction are called reactantsreactants

The final molecules of a chemical The final molecules of a chemical reaction are called reaction are called productsproducts



Reactants Reaction Products

2 H2 O2 2 H2O

Summary Questions:Summary Questions:

Define the terms element and atom.Define the terms element and atom. What are the four most common What are the four most common

elements found in human beings? elements found in human beings? How are covalent and ionic bonds How are covalent and ionic bonds

different?different? What occurs What occurs

chapter 2 review big ideas you should know. concept 2.1: matter consists of chemical elements in...

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