Democritus
1st used the word atom, said they were small hard particles, made of single
material, all different shapes/sizes
atom
smallest unit of an element that maintains the properties of that element
Dalton
-said all things are made of atoms, which can’t be created or destroyed
-atoms of the same element are the same. atoms of different elements are
different
-atoms can join together to form new substances
Thompson
Rutherford
-discovered particles inside the atom, called the negative ones electrons.
-His model is called the plum pudding model.
-He used a cathode ray tube and electric charge to see the particles move
towards the positive charge
-discovered positively charged nucleus. said most of atom is empty space.
-shot particles into gold foil. Some of the particles bounced back, some
deflected, most went straight through.
Bohr
-said that electrons move in certain paths or levels. His model is still used
today
Modern
Atomic
Theory
-electrons are found in electron clouds, regions where electrons are likely to
be. The exact location of electrons cannot be found.
What are the
3 main parts
of the atom?
proton- positive, found in nucleus, mass of 1 AMU
neutron- no charge, found in nucleus, mass of 1 AMU
electron- negative charge, found in cloud around nucleus, no mass
Atomic Mass
Unit (AMU)
Unit of mass for measuring atoms. 1 AMU is equal to the mass of 1 proton or
neutron
Ion
particle that is charged because of an unequal number of protons & neutrons
Atomic
Number
the number of protons in the nucleus of an atom
Isotope
an atom that has the same number of protons but different numbers of
neutrons. Isotopes usually have the same properties, some are radioactive.
Mass
Number
the sum of the protons and neutrons. This will always be a whole number
atomic mass
the average mass of an atom expressed in atomic mass units (AMU). This is
usually a decimal b/c it’s an average
Describe the
4 forces
inside an
atom
gravitational force- gravity exists between the parts of an atom
electromagnetic force- like charges repel, opposite charges attract
strong force- the forces that hold the positively charged nucleus together
weak force- the force that can change a neutron into a proton or electron.