BISC 1111 - lecture 2 chemistry of life

matter

all “stuff” composed of it

anything that takes up space and has mass

rocks & metals, to oils and gasses, to living organisms

living things are made up of non-living components

composed of atoms

atoms

smallest unit of an element that contains all the characteristics of that element

building blocks of matter

element

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

elements in the human body

essential elements- chemical elemnt required for an organisms’ existence

not all organisms require the same elements; plants require 17, whereas humans require 25

trace elements

required for life but in minute quantities

compound

exhibit emergent properties

substance consisting of atoms of two or more different elements combined at a fixed ratio

table salt - two elements fixed in a 1:1 ratio (NaCl)

subatomic particles

make up atoms

neutrons, protons, electrons

neutrons

subatomic particle with No electrical charge, mass of 1.7×10²4g, found in atomic nucleus

protons

single positive electrical charge, with a mass of 1.7×10²4g, found in atomic nucleus

electrons

single negative electrical charge, with mass 1/2000th of a neuron or proton

found moving in the nucleus of an atom

variations among atoms of the same element

all atoms of an element have the same number of protons but may differ in the number of neutrons

isotopes

two atoms of an element that differ in the number of neutrons

radioactive isotopes

decay spontaneously, giving off particles and energy

radiometric dating

scientists measure ratio of different isotopes and calculate how many half-lives have passed since the fossil or rock was formed

“parent” isotope decays into its “daughter” isotope at a fixed rate, expressed as the half-life of the isotope

radioactive tracers

diagnostic tools, used to track specific atoms through metabolic processes in combination with sophisticated imaging instruments

positron emission tomography (PET) scans can detect and monitor cancers

electron energy levels

electrons of an atom differ in their amounts of potential energy based on their distance from the nucleus

changes in potential energy of electrons can occur only in steps or fixed amounts

electrons found in different electron shells, each with a characteristic average distance and energy level

unique properties of elements

chemical behavior of an atom determined by the distribution of electrons in electron shells

periodic table of elements shows electron distribution for each element

left-to-right sequence of elements in each row corresponds to sequential addition of electrons and protons

valence electrons

determine chemical behavior

those in the outermost energy shell

orbital

three dimensional space where an electron is found 90% of the time

chemical bonds

atoms with incomplete valence shells can share or transfer valence electrons with certain other atoms

interactions usually result in atoms staying close together, held by attractions called chemical bonds

covalent bonds

sharing of a pair of valence electrons by two atoms

shared electrons count as part of each atom’s valence shell

molecules

consist of two or more atoms held together by covalent bonds

bonds can be single or double or triple

smallest unit of compounds that retains characteristics of said compound

not all atoms have same “demand” for electrons

atoms in a molecule attract electrons to varying degrees

electronegativity

atoms attraction for the electrons in a covalent bond

the more electronegative an atom is, the more strongly it pulls shared electrons toward itself

nonpolar covalent bonds

atoms share electron equally

always occurs if atoms bonded together are the same element (H2, O2, N2)

also form between two different atoms of similar electronegativities

polar covalent bonds

one atom is more electronegative, and the atoms do not share electron equally

unequal sharing of electrons causes partial positive or negative charge for each atom or molecule

ionic comounds, called “salts”

sodium chloride (NaCl) often found in nature as crystals

NaCl not a molecule, formula for an ionic compound indicates ratio of elements in a crystal of the salt

most salts are quite stable when dry, dissociate quite easily in water

molecular form determines function

molecule’s shape determined by positions of its atoms orbitals

in a covalent bond, s and p orbitals may hybridize creating specific molecular shapes