Atomic Structure

Atomic Structure

·         Subatomic Particles

Neutrons- large with no charge

Proton- large with positive charge

Electron- small with negative charge

Name	Symbol	Relative Mass (Atomic Mass Unit, AMU)	Electric Charge	Location in the Atom
Proton	1p 1	1	+1	Nucleus
Neutron	1n 0	Slightly >1	0	Nucleus
Electron	0   e −1	≈0	-1	Cloud surrounding the nucleus

·         In a neutral atom,

Number of protons = Number of electrons (overall charge is 0)

·         Atomic Number = # of protons = # of electrons

·         If a proton is added to an element’s nucleus, a new element will be produced.

For example, O add one proton, atomic mass from 16 to 17, atomic number from 8 to 9

·         Ions- Atoms that gain or lose electrons

Number of electrons = protons – charge

·         Negatively-charged ion (anion): add a electron (electrons more than protons)

·         Positively-charged ion (cation): lose electrons (protons more than electrons)

·         Mass Number (A): is the total number of protons and neutrons or atomic mass number.

Since Atomic Number = The # of protons, Atomic mass = # of protons + # of neutrons

Number of Neutrons = Mass Number –Atomic Number

Atomic Mass ≈ Mass Number

·         Isotopes are atomic species having the same atomic number (protons) but different atomic masses/mass numbers (neutrons).

·         The molar mass represents an average value of a mixture of isotopes.

Example: Cl-35 = 75.77% and Cl-37 = 24.23%

Average mass = (0.7577 x 35) + (0.2423 x 37) = 35.49 g/mol