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 H 2 O, CO 2, NH 3, O 2 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)