Chapter 4Chapter 4::Chemical Basis of LifeChemical Basis of Life

Atom: the basic unit of Atom: the basic unit of mattermatter

StructureStructure::

Composition of Matter: Composition of Matter: Subatomic ParticlesSubatomic Particles

Proton, Neutron & Electron Proton, Neutron & Electron – Proton = (+) {defines the atom)Proton = (+) {defines the atom)– Electron = (-)Electron = (-)– Neutron = no chargeNeutron = no charge

Protons and Nuetrons are located in the Protons and Nuetrons are located in the nucleusnucleus

Electrons are Electrons are notnot found in the nucleus found in the nucleus – –

– They travel at high speeds throughout the atom in a They travel at high speeds throughout the atom in a series of distinct energy levels that surround the series of distinct energy levels that surround the nucleus. nucleus.

– The existence of these electrons is extremely important The existence of these electrons is extremely important in determining the chemical properties of an atom.in determining the chemical properties of an atom.

An Element: Element – a pure Element – a pure

substance that consists substance that consists entirely of one type of entirely of one type of atomatom..

They are represented They are represented by a one or two letter by a one or two letter symbol on the symbol on the periodic periodic tabletable..

Atomic # = # protonsAtomic # = # protons Atomic mass = mass of Atomic mass = mass of

nucleus (p + n)nucleus (p + n)

What Is An Isotope?What Is An Isotope? The number of protons will never change, but the The number of protons will never change, but the

number of neutrons can vary from atom to the next.number of neutrons can vary from atom to the next. Isotopes of an atom differ in neutron number. Isotopes of an atom differ in neutron number.

(# Protons (# Protons ≠ # neutrons)≠ # neutrons)

RadioisotopesRadioisotopes

Some larger isotopes are unstable Some larger isotopes are unstable and decay giving off radiation and decay giving off radiation (matter & energy)(matter & energy)

Such isotopes are useful in Such isotopes are useful in research and medicineresearch and medicine– ““Biological spies” for body scansBiological spies” for body scans– Radiation treatment for cancerRadiation treatment for cancer

Chemical Chemical CompoundsCompounds

Produced when elements combine to form Produced when elements combine to form substances consisting of two or more atoms. substances consisting of two or more atoms.

Represented by chemical formulas:Represented by chemical formulas:

Water Water (H(H22O)O), Table Salt , Table Salt (NaCl)(NaCl), Sulfuric Acid , Sulfuric Acid (H(H22SOSO44))

Single Molecule : Multiple Molecules:

Forming Bonds:Forming Bonds: Share or Transfer ElectronsShare or Transfer Electrons

In order to achieve In order to achieve stability – an atom stability – an atom will either will either transfertransfer or or shareshare electrons electrons (valence)(valence)

This is achieved This is achieved through either through either ionicionic or or covalentcovalent bonding. bonding.

Ionic Bonding Ionic bondingIonic bonding – involves the – involves the transfertransfer

of electrons from one atom to of electrons from one atom to another (gain or lose).another (gain or lose).

– Ex: NaClEx: NaCl

Covalent BondingCovalent Bonding

chemical chemical bondbond formed formed by the by the sharingsharing of of electrons. electrons.

No elements are No elements are gaining or losing gaining or losing atoms.atoms.

Ex. HEx. H2200

Chemical ReactionsChemical Reactions Atoms within molecules are rearranged to produce new Atoms within molecules are rearranged to produce new

molecules: molecules: – Bonds are brokenBonds are broken– Atoms are rearrangedAtoms are rearranged– New bonds are formedNew bonds are formed

As the law of conservation of mass tells us, matter is not As the law of conservation of mass tells us, matter is not created nor destroyed during a chemical reaction.created nor destroyed during a chemical reaction.

Some reactions absorb more energy than they release Some reactions absorb more energy than they release (endergonic/endothermic)(endergonic/endothermic)

Other reactions release more energy than they absorb Other reactions release more energy than they absorb (exergonic/exothermic)(exergonic/exothermic)

Water:Water: One of the few naturally occurring One of the few naturally occurring

compounds that is liquid at the temperatures compounds that is liquid at the temperatures found on the Earth’s surface.found on the Earth’s surface.

Expands as it changes from liquid to solid.Expands as it changes from liquid to solid.– This is why This is why ice floatsice floats on lakes and rivers on lakes and rivers

High Heat Capacity High Heat Capacity – resists change in – resists change in temperature (a lot of energy stored/released for temperature (a lot of energy stored/released for temp change)temp change)

High Heat of Vaporization High Heat of Vaporization – evaporation requires – evaporation requires a lot of energya lot of energy

Water – A Polar MoleculeWater – A Polar Molecule Water has an uneven

distribution of electrons Since Oxygen is a

bigger atom (more protons) than the hydrogen atoms, the electrons spend more time near the oxygen

This creates a partial charge on each end

This partial charge holds individual water molecules together, makes water excellent at dissolving.

Hydrogen BondsHydrogen Bonds Because of their partial positive &

negative charges, polar molecules like water can attract each other.

The hydrogen atom of one water being attracted to the oxygen atom of another water is an example of hydrogen bonding.

Water acts like a Water acts like a magnet….magnet….

Cohesion, Adhesion & Capillary Cohesion, Adhesion & Capillary ActionAction

Cohesion:Cohesion: attraction (by H-attraction (by H-bonding) between two molecules bonding) between two molecules of the same polar substanceof the same polar substance

Adhesion:Adhesion: attraction (by H-attraction (by H-bonding) between two molecules bonding) between two molecules of the different polar substances of the different polar substances

Capillary Action:Capillary Action: ability of ability of

water to rise in a narrow tube water to rise in a narrow tube against the force of gravityagainst the force of gravity

Surface TensionSurface Tension

MixturesMixtures

The charged regions of water molecules make them good at forming mixtures

– A mixture is a substance composed of two or more elements or compounds that are mixed but not chemically combined

Ex: salt and pepper stirred together– Mixtures made with water are

called solutions and suspensions.

SolutionsSolutions

Solution: a homogenous mixture Solution: a homogenous mixture in which one substance is in which one substance is dissolved into anotherdissolved into another

– A A solutesolute (like sugar) completely dissolves (like sugar) completely dissolves in a in a solventsolvent (like water) like in iced tea. (like water) like in iced tea.

– Water is the best (universal) solvent due Water is the best (universal) solvent due to it’s polarity (charged ends)to it’s polarity (charged ends)

SuspensionsSuspensions Materials Materials do notdo not break upbreak up into into

individual atoms, but particles are individual atoms, but particles are small enough that they small enough that they do not do not settle on the bottomsettle on the bottom of a container. of a container.

Example: Example: bloodblood

Solutions: AcidsSolutions: Acids When some compounds dissolve When some compounds dissolve in water, they break apart into in water, they break apart into individual ions.individual ions.

HCl HCl H H++ + Cl + Cl--

Compounds that release hydrogen ions (HCompounds that release hydrogen ions (H++) into ) into a solution are acids; High [Ha solution are acids; High [H++]]

[ ] means [ ] means concentration ofconcentration of

Characteristics of Acids Characteristics of Acids (do not write)(do not write) Produce HProduce H++ (H (H33OO++) ions in water) ions in water

Taste sour Taste sour

Corrode metalsCorrode metals

React with bases to form salts and waterReact with bases to form salts and water

Are electrolytesAre electrolytes

Solution: BasesSolution: Bases Bases are compounds that release Bases are compounds that release hydroxide ions (OHhydroxide ions (OH--) into a solution) into a solution

NaOH NaOH Na Na++ + OH + OH- -

Produce OHProduce OH-- ions in water ions in water

Characteristics of Bases Characteristics of Bases (do not write)(do not write)

Taste bitter, chalkyTaste bitter, chalky

Are electrolytes (produce electricity)Are electrolytes (produce electricity)

Feel soapy, slipperyFeel soapy, slippery

React with acids to form salts and waterReact with acids to form salts and water

•7 is a neutral pH[H+] = [OH-]

•pH < 7 = acid•pH > 7 = base

•Farther pH from 7, the more acidic or basic

•Every change in pH value corresponds to a ten-fold change in [H+]

Ex) pH 3 is 10x more acidic than pH 4