Chemistry

The Nature of Matter

• To discuss macromolecules, we will have to explore some chemistry

• Everything you’ll need to know about chemistry will fit on these few slides– I promise!

The Basics

• All matter is made of atoms• Every atom has a nucleus with at least one

proton and usually some neutrons– Protons exert a + charge around them– Neutrons have no charge

• These + charges attract electrons which each have a – charge– Electrons are way smaller so they zoom around

really fast and can’t hold still

Chemistry is Electron Behavior

• The number of protons determines what element it is– Where it goes on the periodic

table of the elements

• The reason this matters is because there are fixed slots the electrons fit into, and electrons “want” to fill the slots if possible

Matter and Energy• When an electron “falls” towards the nucleus it

releases energy– May be heat or light– In order to remove an electron you must put the

energy back into it

• Electrons may fall into arrangements that connect two atoms together– These are referred to as bonds– These release energy and in order to break a bond

you must add energy back in

Types of Bonds

• Ionic bond: One atom donates an electron and another atom receives it– The two atoms are then

attracted to each other

• Covalent bond: A pair of electrons split time between the outer shells of two different atoms

Ionic Bonds

• An ionic bond is weak; it dissolves in an environment with many charges– Salt dissolves in water

• Sodium, potassium and calcium are three common metals that form ionic bonds– They donate their electrons to halogens like

chlorine and become cations (positive charges)– They are required in our bodies in specific

amounts, dissolved in our blood and cells

Covalent Bonds

• Covalent bonds are formed as a sharing of electrons between nonmetals– Metals do NOT typically form covalent bonds

• The goal is to have four pairs of electrons for most nonmetals– Carbon has four unpaired electrons so it can make

four covalent bonds– Oxygen has six electrons so only makes two bonds

Covalent Bond Behavior• Sometimes covalent bonds are uneven– Electron spends more time on one end than the other– Anyone who’s shared custody of children knows

sharing is often uneven!• This means the atom with more than 50% time is

slightly negative and the atom with less than 50% is slightly positive– This is a polar covalent bond and may make the

molecule a polar molecule– Polar molecules may interact with each other in a

hydrogen bond

Example of Polar Molecule:

• Water!• Water dissolves salt (ionic

bonds) because the positive and negative atoms mix with the positive and negative charges in the water

• This means water (and other polar chemicals) are slightly “sticky”

Acids and Bases

• If a hydrogen atom loses its electron it may be written as H+ but it is basically a lone, free proton

• Water is full of free protons that break off, leaving an OH- to match it– If there are more free protons than there are in a

solution compared to OH- it is an acid– If there is a lack of free protons it may be referred

to as a base

pH Number

• Pure water is pH7 which is neither acid nor base, lower numbers are acid– Why does an acid have a lower

pH number?• Which number is bigger, 10-7 or

10-4?– When the concentration of

protons is high, the negative exponent gets smaller and the pH gets lower

Why Does This Matter?• Different body parts have

different chemicals and thus have different pH levels!– Where is a body part that is

acidic?• If you mix a weak acid and a

weak base together you can create a buffer which resists pH change– Our blood has a buffer system to

prevent pH changes from killing us! Very handy.