ch 2: the chemical context of life

compound

atoms joined by bonds; two or more elements in a fixed ratio

element

substance that cannot be broken down to other substances by chemical reactions

emergent properties

a compound that has characteristics different from those of its elements

elements that make up ~96% of living matter

CHON

atom

smallest unit of matter that still retains properties of an element

subatomic particles

1) neutrons (no charge)

2) protons (positive)

3) electrons (negative)

atomic nucleus

formed by protons and neutrons

atomic number

number of protons (or electrons)

mass number

protons + neutrons

atomic mass

atom’s total mass = (kinda) mass number

isotopes

atoms of an element with

1) same # of protons

2) diff # of neutrons

3) diff mass #

radioactive isotopes

decay spontaneously

energy

capacity to cause change

potential energy

the energy that matter possesses because of its location or structure

electron shell

where electrons are found, each with a characteristic avg distance and energy level

valence shell

outermost shell containing electrons

valence electrons

electrons in valence shell; determines chemical behavior of atom

full valence shell

fully stable atom

incomplete valence shell

atoms can share or transfer valence electrons with other atoms to become stable

chemical bonds

type of attraction that holds atoms together

covalent bonds

sharing of a pair of valence electrons by two atoms; counts as a part of each atom’s valence shell; can happen between atoms of the same element OR diff elements

molecule

two or more atoms held together by COVALENT bonds

single (covalent) bond

sharing of one pair of valence electrons

double (covalent) bond

sharing of two pairs of valence electrons

electronegativity

an atom’s attraction for the electrons in a covalent bond (the stronger, the more the atom pulls shared electrons towards itself)

nonpolar covalent bond

atoms share electrons equally

polar covalent bond

atoms share electrons unequally → causes partial pos or neg charge for each atom/molecule

what type of bond is the strongest?

covalent bonds

what bonds are the weakest?

ionic and hydrogen bonds

what does a weak bond mean?

are reversible but can help maintain molecular shape and function

ionic bond

electrons are transferred from one atom to another, creating ions (anions and cations attract each other)

ions

creating two oppositely charged atoms or molecules

cation

positively charged ion (+)

anion

negatively charged ion (-)

ionic compounds

ionic bonds form salts

hydrogen bond

a hydrogen atom covalently bonded to one electronegative atom is also attracted to another electronegative atom

chemical reaction

making and breaking of chemical bonds

reactants

starting molecules of a chemical reaction

products

final molecules of a chemical reaction