UNIT 3: COUNTING

ATOMS

SUBATOMIC PARTICLES

PROTON Determines the element

Number of protons CANNOT change for an element

Common charge notation is +1 Mass (g) = 1.673 x 10-24 Mass (amu)= 1.0073 = 1

NEUTRON Common charge notation is 0. No

charge! Mass (g) 1.675 x 10-24 (same mass as

proton) Mass (amu)= 1.0082 = 1 Number of neutrons CAN change for an

element ISOTOPES

Stabilizes nucleus by nuclear force

ELECTRON Common Charge notation is -1 Mass (g) of e- = 9.109 x 10-28

Mass (amu)= .0006 = 0 Number of electrons CAN change for an

element IONS

Responsible for chemical reactivity, forms bonds

Proton Neutron Electron

Location Nucleus Nucleus Outside of nucleus

Common charge

+ 0 _

Mass, g 1.673x10-24 1.675 x 10-24 9.109 x 10-24

Mass, amu 1 1 0

CHECK YOUR UNDERSTANDING Which subatomic particle can NOT

change for an element and gives it’s identity?

Which subatomic particle stabilizes the nucleus?

SECTION 3: COUNTING ATOMS Atomic Number: The number of protons

in each atom of that element. Unique to EACH element, never changes!!

Neutral atoms: proton #= electron #

Example:1. How many protons does Beryllium (Be)

have? How many electrons?2. How many protons does Gold (Au)

have?

ISOTOPE Isotopes: Are atoms that have

different number of neutronsSo masses are different

Example of isotopes:

MASS NUMBER Mass Number: The total number of

protons and neutrons in the nucleus

HYPHEN NOTATION Element- Mass number

What is the hyphen notation of lithium if the mass number is 4?

Common isotopes of carbonCarbon-12Carbon-13Carbon-14

How many protons do all the carbon isotopes have?

How many neutrons do each of the carbon isotopes have?

ATOMS Atoms are Neutral because they have

the same number of electrons and protonsYou will assume this unless indicated

otherwise

IONS Ions :are when the electron number and

proton number are different leading to a net charge.

What charge would Aluminum have 13 protons and 10 electrons?

NOTE: YOU WILL ALWAYS ASSUME ATOMS ARE NEUTRAL (protons = electrons) UNLESS TOLD OTHERWISE

APE MAN Atomic #= Proton #= Electron #

(because we assume atoms are neutral)

Mass #= Atomic # + Neutron #

APE MAN Number of protons= Atomic number Number of electrons = Number of protons

(in a neutral atom) Number of neutrons = Mass number–

Atomic number

Symbol Atomic #

Mass # # of protons

# of electrons

# of neutrons

Na 11

15 31

AVERAGE ATOMIC MASS Average atomic mass is the weighted

average of the atomic masses of the naturally occurring isotopes of an elementThis number appears below the

element symbol on the periodic table.