Chemistry for Biologists (Part 1)

Elements

The simplest form of matter, cannot be broken down by chemical means

All matter is made of

elements

96% of all mass of all living things are made up of

Oxygen, Carbon, Hydrogen, Nitrogen

4% of biomass are made of

Calcium, Phosphorus, Potassium, Sulfur, Sodium, Chlorine, Magnesium

Atom

The smallest units of an element

Parts of an atom

Proton, Neutron, Electron

Protons

In the nucleus, positive (+) charged

Neutrons

In the nucleus, neutral

Isotopes

Same element, different number of neutrons

Can cause spontaneous decay

Electrons

Negative (-) charged, outside of the nucleus, and essentially massless

Valence Electronss

Electrons that are in the outermost shell, called the Valence shell

Atoms are

effectively neutral, as most atoms have the same amount of protons (+) and electrons (-)

Chemical behavior of an atom

• Determined by the distribution of electrons in the electron shells

• Valence shells have the most impact

Noble Gases

Elements with full valence shells

• Chemically inert

Atomic Bonding

How atoms with incomplete valence shells can share/transfer electrons with other atoms

Ionic bonding

• Formed between ions with opposite charges

• An atom donates its electron to another, resulting in charged ions

• Na⁺ + Cl^- → Na^-Cl⁺

• Chlorine donates an electron in order to bond

• Metal+nonmetal

Covalent bond

• Atoms share an electron/electrons

• Can be polar (charged) or nonpolar

• H₂O

• non-metal+non-metal

Hydrogen Bonds

Attraction between a hydrogen atom already bonded to an electronegative atom and another electronegative atom

• important in proteins, nucleic acids, and water

Atomic number = ?

Number of protons in the nucleus

Mass number

Number of Protons + Number of Neutrons

• Average of all Isotopes

Cations

Positive Charge

Anion

Negative Charge

• Think Antivillan

Anion (-) Plus Cation (+) =

Ionic Bond!

Molecule

Two or more atoms are held together by covalent bonds

Non-polar covalent bonds

Electrons are shared equally

Polar Covalent bonds

electrons are shared unequaly

Single Covalent vs Double Covalent

Single covalent has 1 pair of electrons that are shared, Double covalent has 2 pairs of electrons that are shared

Structural Formula

H-H

Molecular formula

H_2, Ca₃

Van der Waals

• The weakest interaction

• All molecules have these

• attraction between molecules that are close are a result of these charges