ch. 2 biology #4: the chemical basis of life

matter

anything that occupies space and has mass

3 physical states of matter

solid, liquid, gas

element

substance that cannot be broken down to other substances by normal chemical means

compound

substances with two or more elements combined in a fixed ratio

the big six elements in the body

O, C, H, N, P, Ca

oxygen, carbon, hydrogen, and nitrogen are the building blocks of…

proteins, carbohydrates, lipids

phosphorus and calcium are major components of…

bones and teeth

trace elements

elements in small amts in the body

• some needed by all organisms (eg. iron)

• some only needed by some species

atom

Smallest unit of matter that still retains the
properties of an element

3 subatomic particles of an atom

1. proton

2. neutron

3. electron

nucleus

central core of an atom

• electrons form a cloud of negative charge around the nucleus

atomic number

number of protons

mass number

sum of protons and neutrons in a nucleus

atomic mass

weight of an atom

what unit is mass number expressed in

Da - Daltons

isotopes

Atoms that have the same number of
atoms that have the same number of protons and behave the same way chemically but have different numbers of neutrons

radioactive isotope

nucleus is unstable and decays spontaneously, releasing particles and energy (radiation)

what can radioactive molecules be used for?

dating fossils, medicine (chemical tags / tracers, treatment that targets), research

what determines an atom’s chemical property

distribution of electrons

valence shell

outer shell of an atom

valence electrons

electrons found on valence shell

inert atoms

atoms with complete outer shells

• don’t interact with other atoms

chemical bonds

attractions and interactions between atoms

ionic bond

transfer of electrons from one atom to another

covalent bond

atoms share electrons

bonding capacity (valence)

number of covalent bonds the atom can form

molecule

two or more atoms bound together by covalent bonds

electronegativity

an atoms measure of attraction for shared electrons

non polar covalent bonds

electrons are shared equally because two atoms have the same electronegativity

polar covalent bonds

electrons are pulled closer to the more electronegative element

• one atom has a slightly negative charge, one has a slightly positive charge

• oxygen is one of the most electronegative, almost always makes a polar covalent bond