Chemistry - Atomic Theory

atom

the smallest part of an element that retains it’s properties

cathode ray

a ray that originates from the cathode and travels to the anode

nucleus

tiny dense region in the atom where positive charge and almost all the mass is contained

Properties of an atom

the atom is the smallest part of an element that retains it’s properties ‘when a group of atoms bond and act as a group, it’s called a molecule

Dalton

atomic theory & postulates

• all matter is made up of indivisible atoms which can’t be created nor destroyed

• all atoms of a given element are identical

• atoms of different elements combine in fixed whole number ratios to form compounds

Thomson

discovered the electron

cathode ray

plum pudding model - negative charges embedded in a sea of positive charges

rutherford

discovered proton proposed nucleus

gold foil experiment - passed thru the gold foil and & deflected off of a metal screen

ions

an atom that has lost electrons will have a positive charge

an atom that has gained electrons will have a negative charge

atoms

same number of protons no matter what

isotopes

different number of neutrons

mass number

usually protons + neutrons

identifies each isotope of an element (H-1) & is the sum of atomic number and neutrons & IS A WHOLE NUMBER

atomic mass

the number with tons of decimals but actually it’s a weighted average of the masses bc of the different isotopes, like H-1, H-2, H-3 have different masses

weighted average mass of that element’s isotopes

atomic mass unit (amu)

1/12 mass of carbon-12