chemistry - key concepts in chemistry: atomic structure (1.1 - 1.12)

1.1 Dalton atomic model

all matter made up of tiny particles called atoms

atoms - tiny, hard spheres, cannot be broken into smaller parts

atoms can’t be created/destroyed

atoms in element are identical

each element has its own type of atom

1.1 development of Dalton atomic model

thought cathode rays contained atoms leaving negative electrode

Thomson found particles in rays were lighter than atoms

so cathode rays contain subatomic particles - electrons

1.2 structure of atom

tiny nucleus in centre containing protons & neutrons

surrounded by fast moving electrons in shells

1.3 protons, neutrons, electrons - relative charge & relative mass

1.4 why do atoms contain equal numbers of protons & electrons?

no overall charge - charges cancel out

1.5 size of nucleus

very small compared to overall size of atom

1.6 where is most of atom’s mass?

concentrated in nucleus

1.7 mass number definition

total number of protons & neutrons in atom

atomic number definition

number of protons

1.8 number of protons in atoms of same element

same number of protons

this number (atomic number) is unique to that element

1.9 isotopes definition

different atoms of same element with same number of protons (same atomic number) but different numbers of neutrons (different mass numbers)

1.10 calculate numbers of protons, neutrons & electrons given atomic number & mass number

protons = atomic number = 11

electrons = protons = 11

neutrons = mass number - atomic number = 23 - 11 = 12

relative atomic mass definition

mean mass of an atom of an element compared with carbon-12

1.11 why are some relative atomic masses not whole numbers?

all elements exist as mixtures of isotopes

RAM takes into account all isotopes of element & amounts of each

1.12 calculate RAM of element from relative masses & abundances of its isotopes