Elements

Differences in the atoms that make up the elements

Current model of the atom

Nuclear atomAlmost all of the mass of the atom is

located in the nucleusAll of the volume of the atom is made

up by the electron cloud, which is mostly empty space

The Nuclear Atom

Proton

Has a charge of 1+Has a mass of approximately 1

amu (atomic mass unit)Found in the nucleusThe number of protons identifies

the type of atomThe number of protons = the

atomic number of the element

Electrons

Have a charge of 1-Have a negligible mass (1/2000 of a

proton)Found in the electron cloud in

orbitalsAre the particle of the atom that are

responsible for the chemical bondsNeutral atoms have the same

number of electrons as protons

Neutrons

Are neutral, have no chargeHave a mass of approximately 1

amuFound in the nucleusAre the particle of the atom that is

responsible for isotopes

What is an Isotope?

Atoms with the same number of protons (so they are the same element)

But they have different numbers of neutrons

Thus, they are atoms of the same element that have different masses

Two isotopes of Sodium

How do we write that?

23

11

Na

Or

Na-23

Na-23 has

11 protons (atomic number)11 electrons (neutral atom)12 neutrons (atomic mass of 23

amu)

Na-23 is an isotope

It has the same number of protons as other atoms of sodium

It is a neutral atom (no charge, same number of electrons as protons)

It has different number of neutrons than other sodium atoms

Atomic Numbers

Atomic number is the number of protons in an atom

Mass number is the sum of the number of neutrons and the number of protons in a given atom

The atomic mass number on the periodic table is a weighted average mass of all known isotopes of that element