Essential Chemistry for Biology

Matter is made of atoms

Elements found in biological molecules (Fig. 2.2)

Atomic structure (Fig. 2.4)

Atomic Number• Atomic number = # protons• Each element has its own number of

protons– Carbon has 6 protons. Oxygen has 8.

• If you change the number of protons you change the element

• If you add another proton to carbon it will have 7 which makes it nitrogen

Atomic mass

• Mass of subatomic particles– Protons = 1 unit– Neutrons = 1 unit– Electron = 0 (not zero, but really, really, small)

• Mass = # protons + # neutrons• Different masses of the same element are

called isotopes

Some isotopes are unstable

• Radioisotopes decay and emit particles until they are stable

• Carbon-14 “decays” to Nitrogen 14

Radioisotopes decay at a fixed rate

• 50% of C-14 in any substance will decay in 5700 years

• If we measure the amount of C-14 and the amount of C-12 in a sample we could estimate the age of the sample (Carbon dating)

• Other isotopes are used for dating rocks millions or billions of years old

Potassium-Argon Decay (NIB)

Electrons Exist in Shells (NIB)

Atomic charges

• The overall charge of an atom = # protons - # electrons

• If an atom has a (+) or (–) charge it is an ion• Metals normally form (+) ions• Non-metals form (–) ions• Ions can only be formed by changing the

number of electrons in an atom

Four Elements (Fig. 2.5)

Bonds

• Atoms can form bonds with other atoms to form molecules

• Two types of bonds

1. Covalent

• Two atoms share their outer electrons forming a bond

• H2O, CO2, NH3, O2 are held together by covalent bonds

Molecular Compounds with Covalent Bonds (Fig. 2.7)

2. Ionic Bonds (Fig. 2.6)A positive ion (metal) can bond with a negative ion (non-metal) to form an ionic bond.

Sodium (Na) and chlorine (Cl) form ionic bonds in table salt

Intermolecular Forces

• Polar molecules have a slightly positive end and a slightly negative end

• Polar molecules form weak polar bonds with other polar molecules

• Polar molecules containing hydrogen will form hydrogen bonds with other polar molecules.

• Water is a polar molecule.

Hydrogen Bonds (2.8)

Hydrogen Bonds (Figure 2.13)

Water is important to life

• Forms hydrogen bonds with itself and other polar molecules (Hydrophilic)

• Forms a solution for many chemical reactions inside our cells

• Moderates temperature• Required for photosynthesis

Water transport in a tree (Fig 2.9)

Water is a solvent for ionic compounds (Fig. 2.14)

Surface Tension

Acids and Bases

• Acids are molecules that give up a positive hydrogen ion (H+)

• Bases are molecules that accept a positive hydrogen ion (H+)

• How readily an atom accepts or donates a hydrogen is indicated by its pH

• Acids - 0 < pH < 7• Bases - 7 < pH < 14• Water pH = 7 (Neutral)

pH Scale (Fig. 2.16)