Chapter 2: The Chemistry of Life

Basic Chemistry

ATOM: The basic building block of all matter; the smallest particle of an element that still retains properties of that element

All atoms have a Nucleus, which is the central part of the atom; it contains protons; and has an overall positive charge.

– PROTON: (+)ve charged subatomic particles located in the nucleus; charge of +1

– NEUTRON: (-/+) neutral (no charge) subatomic particles located in the nucleus; charge of 0.

Protons and neutrons have about the same mass. – ELECTRON: (-) Negatively charged subatomic particles

located in electron orbitals around the nucleus; their mass is tiny, about 1/1840 the mass of a proton; charge or -1

Atoms have equal numbers of protons and electrons, their overall charge is zero (neutral)

ELEMENT – Matter containing only one type of atom.

SYMBOL ATOMIC NUMBER

– The number of protons ATOMIC MASS

– The number of protons + neutron

ISOTOPESAtoms of the same element

that have different numbers of NEUTRONS.

Chemical BondsWhen two or more

ELEMENTS chemically combined by bonding.

Chemical Bonds

IONIC BONDS

– An attraction between atoms where electrons transferred

Ions

A form of an atoms where electrons are either lost or gained.

Ions have either a positive or negative charge.

Sodium Chloride (NaCl): An Ionic Bond

Chemical Bonds

COVALENT BONDS Two atoms SHARE electrons (this forms very

strong bonds). Example: Water (H2O) = 2 hydrogen + 1 oxygen

– MOLECULE – two or more ATOMS covalently bonded.

Water (H-O-H): A covalent bond

Properties of Water

Water covers ¾ of Earth’s Surface

Water is the single most abundant compound in most living things.

The Water Molecule

Water has several important physical properties:

– It is a liquid at temperatures found over much of Earth’s surface.

– Water expands as it freezes.– Water is more dense than ice, so ice

floats. Which allows for fish and plant life to survive below the ice.

The Water Molecule

Overall, water is a neutral molecule.

However, a water molecule is polar.

Although the entire molecule has equivalent numbers of protons and electrons, the electrons are unevenly distributed.

The Water Molecule

The oxygen has a strong pull on the electrons near the oxygen making the probability of finding those electrons near the oxygen greater than finding them near the hydrogen atoms.

This gives the oxygen end of the water molecule a slightly negative charge and the hydrogen ends of the water molecule a slightly positive charge.

This uneven distribution of charge on a molecule is called polarity.

When large numbers of water molecules get together, hydrogen bonding occurs.

Properties of Water

COHESION – an attraction between molecules of the same substance.

An example of cohesion is called surface tension- water molecules on the surface of a body of water cling tightly together and allow small organisms to survive on its surface.

ADHESION – an attraction between molecules of different substances.

Cohesion and adhesion work together to produce capillary action.

The water molecule

ADHESION – an attraction between molecules of different substances.

Cohesion and adhesion work together to produce capillary action.

Adhesive forces cause the water to climb up the inside of the alls of the tubes, and cohesive forces allow the water molecules to cling to each other as it crawls up the tube.

Solutions and Solutions and SuspensionsSuspensions

Solution and SuspensionsSolution and Suspensions Water is often found as a Water is often found as a - a material - a material

composed of composed of substancessubstances

that arethat are

mixturetwo or moretwo or more

physically mixed together.physically mixed together.

Example:Example:1) Dissolving sugar into hot tea1) Dissolving sugar into hot tea2) Dissolving salt into hot water2) Dissolving salt into hot water

Solution and SuspensionsSolution and Suspensions Two types of mixtures can be made with water:Two types of mixtures can be made with water:

SolutionSolution – a mixture where a substance is evenly – a mixture where a substance is evenly mixed in another substance.mixed in another substance.

The substance in the smallest amount, which is The substance in the smallest amount, which is

is called theis called the

The substance in the greatest amount, which The substance in the greatest amount, which

is called the is called the

dissolveddissolved

solute.solute.

dissolves the solutedissolves the solute solvent.solvent.

Solution and SuspensionsSolution and Suspensions

has the ability to dissolve many has the ability to dissolve many substances and thus is called thesubstances and thus is called the

General Solubility Rule:General Solubility Rule:

WaterWater

universal solvent.universal solvent.

- Like dissolves like- Like dissolves likePolar substances dissolve polar Polar substances dissolve polar

substancessubstances

MIXTURE – mixed but not chemically combined.

SOLUTION – uniform mixture– SOLVENT – dissolves other substances.

– SOLUTE – dissolves in the solvent.SUSPENSION – temporarily mixed

Acids, Bases, pHAcids, Bases, pH

Water can Water can react and divide/dissolvereact and divide/dissolve into into two ions:two ions:

HH22O O H + H + OH OH

- Scientists have devised a scale to Scientists have devised a scale to measure the amount of measure the amount of hydrogen ionshydrogen ions that exist in solutions calledthat exist in solutions called pH pH..

+ -

Acids, Bases, pHAcids, Bases, pH

The pH scale ranges from 0-14.The pH scale ranges from 0-14. When a solution has When a solution has an equal number of H an equal number of H

and OH ionsand OH ions such as water, it is assigned a such as water, it is assigned a neutralneutral pH, which is 7 on the pH scale. pH, which is 7 on the pH scale.

When a solution has a When a solution has a high H concentrationhigh H concentration then it is assigned an then it is assigned an acidicacidic pH, which is a pH, which is a number number less than 7less than 7 on the pH scale. on the pH scale.

When a solution has a When a solution has a low H concentrationlow H concentration then it is assigned a then it is assigned a basicbasic pH, which is a pH, which is a number number greater than 7greater than 7 on the pH scale. on the pH scale.

+

-

+

+

-

Acids, Bases, pHAcids, Bases, pH

The pH inside human cells must be kept The pH inside human cells must be kept close to close to neutralneutral, between , between 6.5 and 7.56.5 and 7.5. If a . If a chemical with a lower or higher pH enters chemical with a lower or higher pH enters the cell, it could disrupt chemical the cell, it could disrupt chemical reactions there and thus disrupt the cell’s reactions there and thus disrupt the cell’s homeostasis.homeostasis.

Acids, Bases, pHAcids, Bases, pH

Therefore, cells contain weak Therefore, cells contain weak acids oracids or bases called bases called buffersbuffers which work to which work to prevent changes in pHprevent changes in pH inside cells that inside cells that are too acidic or too basic. are too acidic or too basic. For example, the skin has a surface film that For example, the skin has a surface film that

is acidic and it acts as a buffer against is acidic and it acts as a buffer against strong bases like Clorox. strong bases like Clorox.