Early Scientists
He was the first to propose that all matter is made of tiny, indivisible particles called atoms.
Democritus
This subatomic particle has a positive charge.
proton
Dalton’s model pictured atoms as these solid objects.
solid spheres
The number of protons in an atom determines this.
atomic number
The smallest particle of an element that retains its properties.
atom
He developed the first modern atomic theory in the early 1800s.
John Dalton
This subatomic particle has no charge.
neutron
Thomson’s model was also called this sweet nickname.
plum pudding model
The sum of protons and neutrons in an atom is called this.
mass number
The nucleus makes up this percentage of an atom’s total volume.
a very small fraction (less than 1%)
He discovered the electron using the cathode ray tube experiment.
J.J. Thomson
This negatively charged particle moves outside the nucleus.
electron
Rutherford’s model introduced this central feature.
nucleus
Atoms of the same element with different numbers of neutrons are called this.
isotopes
This particle was discovered last — proton, electron, or neutron?
neutron
He conducted the gold foil experiment and discovered the nucleus.
Ernest Rutherford
The nucleus of an atom contains these two types of particles.
protons and neutrons
Bohr’s model showed that electrons move in these.
energy levels or orbits
An atom that has gained or lost electrons is called this.
ion
This element’s atoms have 6 protons.
carbon
He proposed that electrons orbit the nucleus in fixed energy levels.
Niels Bohr
The mass of an atom comes mainly from these particles.
protons and neutrons
The modern model describes electrons as existing in this region of probability.
electron cloud
The atomic mass on the periodic table is a weighted average of these.
isotopes
The most abundant type of atom is the universe is
the hydrogen atom