ch 2 the molecules of life

elements

consist of only one type of atom

CHNOPS

major elements essential for life: Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus, and Sulfur.

atom

the smallest unit of an element, consisting of protons, neutrons, and electrons.

neutrons

neutral, uncharged particles

protons

positively charged particles

electrons

negatively charged

an atom has a _____ charge

neutral; bc it has equal number of protons and electrons

center of nucleus contains

protons & neutrons

electrons form a

cloud

atomic number

number of protons in nucleus

mass number

sum of protons and neutrons

electrons move in a

cloud around the nucleus

first shell contains

2 electrons

second shell contains

8 electrons

octet rule

atoms are most stable with filled outer shell (exceptions are hydrogen and helium)

valence electrons

electrons in an atom’s outermost shell

valence electrons determine

chemical reactivity

ions

atom that has gained or lost electron(s)

anions

GAIN electrons (negatively charged)

cations

LOSE electrons (positively charged)

ionic bonds form because of

attraction bw negative and positive charges

molecule

two or more atoms joined together by COVALENT bonds

compound

molecule containing atoms of different elements

polar covalent bonds

unequal sharing of electrons (one atom more electronegative than the other)

non polar covalent bond

equal sharing of electrons

when polar covalent bonds form, it results in

a slight change in charge

when water forms, oxygen is _______ and causes hydrogens to have a _________

partially negative (s-) bc it is more EN pulling electrons toward it; partially positive charge (s+)

hydrogen bonds

weak , short lived bonds formed when hydrogen atom in polar molecule is attracted to EN atom in same or diff polar molecule