Ch. 2 Water and carbon

four most common types of atoms that constitute 96% of the matter in organisms

• Oxygen

• Carbon

• Hydrogen

• Nitrogen 

atomic number

number of protons in an atom's nucleus.

• Determines the element

atomic number of the element Carbon

6

mass number of an atom

total number of protons and neutrons in its nucleus

isotopes

Forms of an element that have different numbers of neutrons

and therefore different mass numbers

valence shell

outermost electron shell

The aspect of an atom's structure determines how it forms chemical bonds

The number of valence electrons

Max number of valance electrons in the first and second shell

1st - 2

2nd - 8

How many valence electrons does a carbon atom possess

4

Under what condition are atoms most stable

When their valence shells are full

• can be filled by forming chemical bonds

covalent bond

a chemical bond formed when unpaired valence electrons are shared between two atoms

How many covalent bonds can an atom of carbon typically form

4

molecule

formed when 2 or m0re atoms are held together by covalent bonds

compound

a molecule that is made up of atoms from different elements

electronegativity

The ability of an atom to attract shared electrons in a chemical bond

what atoms commonly found in biological molecules are quite electronegative

Oxygen and Nitrogen

Non-polar covalent bond

a covalent bond where electrons are shared evenly between two atoms

polar covalent bond

a covalent bond where electrons are shared unevenly between atoms

• due to uneven electronegativity

• i.e. O-H bond

δ− atom in a polar covalent bond

the more electronegative atom gains a partial negative charge

ionic bond

a bond where the difference in electronegativity between atoms is extremely large so electrons are completely transferred

ion

An atom or molecule that carries an electrical charge due to the loss or gain of electrons

Ionic bonds are the attractive forces between _____ charged ions

oppositely

What determines the number of covalent bonds an atom can make

The number of unpaired electrons in its valence shell.

What is the characteristic V-shape of a water molecule (H₂O) caused by

The two unshared electron pairs on the oxygen atom

In a water molecule, the oxygen atom has a partial _____ charge, while the hydrogen atoms have a partial _____ charge

negative; positive

hydrogen bond

bond forms between water molecules due to the attraction of partial opposite charges

hydrophilic

Molecules that are 'water-loving' because they are ionic or polar

Why do hydrophilic substances like salt (NaCl) dissolve in water

They interact with the partial charges of water molecules

hydrophobic

Molecules that are 'water-fearing' because they are uncharged and nonpolar

Cohesion

the tendency of water molecules to stick to each other

Adhesion

the tendency of water molecules to stick to other surfaces

acid

A substance that donates hydrogen ions (H⁺) in a chemical reaction

base

A substance that accepts hydrogen ions (H⁺) or releases hydroxide ions (OH⁻)

pH

measures the concentration of hydrogen ions

a change of one pH unit represents a _____ difference

tenfold (10x)

buffer

minimize changes in pH by donating or accepting H+ ions

Organic compounds

Molecules that contain the element carbon

What is the most abundant element found in human cells by mass (not including water)

Carbon

primary function of lipids in a cell

form cell membranes and store energy

functional group with the formula NH₂

Amino group

• acts as a base by attracting a proton

functional group with the formula -COOH

Carboxyl group

• acts as an acid by donating a proton

functional group with the formula -OH

Hydroxyl

• increases a molecule's solubility in water

functional group with the formula -PO₄^2-

Phosphate group 

• critical for storing and transferring energy

functional group with the formula -SH

Sulfhydryl

• important for stabilizing protein structure through the formation of disulfide bonds

What type of bond forms between two adjacent carbon atoms that share two pairs of electrons

A double bond