3-3 Modern Atomic Theory

By Ms. Pacheco

Parts of the Atom

NAME CHARGE MASS LOCATION

Proton

Neutron

Electron

Parts of the Atom

NAME CHARGE MASS LOCATION

Proton +1

Neutron

Electron

Parts of the Atom

NAME CHARGE MASS LOCATION

Proton +1

Neutron 0

Electron

Parts of the Atom

NAME CHARGE MASS LOCATION

Proton +1

Neutron 0

Electron -1

Parts of the Atom

NAME CHARGE MASS LOCATION

Proton +1 1 amu

Neutron 0

Electron -1

Parts of the Atom

NAME CHARGE MASS LOCATION

Proton +1 1 amu

Neutron 0 1 amu*

Electron -1

Parts of the Atom

NAME CHARGE MASS LOCATION

Proton +1 1 amu

Neutron 0 1 amu*

Electron -1 0

Parts of the Atom

NAME CHARGE MASS LOCATION

Proton +1 1 amu Nucleus

Neutron 0 1 amu*

Electron -1 0

Parts of the Atom

NAME CHARGE MASS LOCATION

Proton +1 1 amu Nucleus

Neutron 0 1 amu* Nucleus

Electron -1 0

Parts of the Atom

NAME CHARGE MASS LOCATION

Proton +1 1 amu Nucleus

Neutron 0 1 amu* Nucleus

Electron -1 0 Electron cloud

* Neutrons are slightly larger than protons

** Electrons are so small that their mass is said to be negligible

Henry Moseley

• A British scientist , he is a student of Rutherford

• In 1913, he makes one of the most important discoveries in chemistry. He found out that an atom’s identity comes from its # of protons (atomic number).

• Moseley was 26 at the time!• 1915: Sadly, Moseley is killed in battle

in Turkey during WWI.

Said Millikan of Moseley…

• “…Had the European War had no other result than the snuffing out of this young life, that alone would make it one of the most hideous and most irreparable crimes in history."

Henry Moseley in his lab…

From Moseley’s ideas, we now know…

• That since an atom has a neutral charge, then the number of protons must equal the number of electrons.

• That an atom that loses or gains electrons has a charge and is known as an ion.

How to find the charge of an ion…

Charge = # P - #E

A magnesium ion has 12 protons and 10 electrons. What is its charge?

Charge = # P - #E= 12-10

= +2Mg+2+2

Isotopes…

Are atoms that have the same number of protons, but a different number of neutrons.

Mass number…

• Is the sum of an isotopes protons plus neutrons.

• Is sometimes written at the end of the atom’s name. Ex: carbon-14

carbon-12 v’s carbon-14

• Both are carbon, so both have 6 protons

• Their mass numbers are 12 and 14.

• Due to subtraction, carbon-12 has 6 neutrons and carbon-14 has 8.

Atomic Mass…

• Is the average mass of an element’s atoms as they appear in nature.

• The atomic masses of all elements are based on the atomic mass of the carbon-12 atom.

Chlorine’s Isotopes

Chlorine-35 75.53%

Chlorine-37 24.47%

Therefore, the average mass (atomic mass) of chlorine is 35.45.