Topic 1) Key concepts in chemistry Flashcards
what are the 3 ideas in John Dalton’s theory about the atom?
-atoms cannot be created
-atoms of the same element are exactly the same and atoms of different elements are different
-atoms join with other atoms to make new substances
what discovery caused the original Dalton model of an atom to change?
the discovery of subatomic particles
how did JJ Thomson discover the electron?
-thomson experimented with a cathode ray tube
- the beam moved towards the positively charged plate so he knew that the particles must have a negative charge
describe the atomic model proposed by JJ Thomson
plum pudding model
negatively charged electrons scattered through a positively charged material
what did Ernest Rutherford discover from his gold foil experiment?
he shot a beam of positively charged particles at sheet of gold foil
- most particles passed straight through suggesting that atoms were mostly empty space
- a few particles were deflected and a few bounced directly back showing that there must be a tiny, dense and positively-charged nucleus
describe Rutherford’s new model of the atom
-mass is concentrated in the central nucleus
-mostly empty space
-electrons travel in random paths around the nucleus
what is the radius of the nucleus?
1x10^-14
what are the relative masses of protons, neutrons and electrons?
proton - 1
neutron - 1
electron - 1/1836
what are the relative charges of protons, neutrons and electrons?
protons - +1
neutrons - 0
electrons - -1
what do atoms contain equal numbers of protons and electrons?
atoms are stable with no overall charge
protons are positively charged and electrons are negatively charged
where is the mass of an atom concentrated?
in the nucleus
what does the atomic number of an atom represent?
the number of protons
what does the mass number of an atom mean?
the mass number is the number of protons and neutrons found in the nucleus of an atom
what is an isotope?
atoms with the same number of protons, but a different number of neutrons
