Atomic Mass

Isotopes, Ions and Average Atomic Mass

By NABS

PRACTICE:

​ELEMENT	​ATOMIC #	​MASS	​PR	​N	​E
​	​	​	​	​	​
​	​	​	​	​	​
​	​	​	​	​	​
​	​	​	​	​	​

ISOTOPES:

• Same Element

• Different Mass Number

• WHICH MEANS DIFFERENT # of NEUTRONS

Multiple Choice

Which has more protons?

• neither

• carbon - 12

• carbon - 13

Multiple Choice

Which has more electrons?

• neither

• carbon - 12

• carbon - 13

Multiple Choice

Which has more neutrons?

• neither

• carbon - 12

• carbon - 13

What does changing # of Neutrons do?

• Neutrons make atoms stable

• Unstable = Wants to fall apart

• Fall Apart = Split into smaller atoms

• Split Apart = RADIOACTIVE

What decay of Uranium - 238 looks like.

Average Atomic Mass

• DIFFERENT than Mass Number

• Average of all of the isotopes of an atom found in nature.

How they get that number

• % abundance of that isotope x actual mass of that isotope

• add together

• divide by 100 (if you didn't put into percentage first)

How to tell which isotope is more abundant?

• CLOSEST TO ROUNDED AVERAGE ATOMIC MASS

• So the most abundant isotope of Gold would be?

• Gold - 197

Ions

• Ion means charged atom

• To be charged it needs more or less electrons than protons

• more electrons = NEGATIVE

• less electrons = POSITIVE

Ion Notation

• Same as isotope

• includes charge in upper right

• + means LESS ELECTRONS than PROTONS

• (-) means MORE ELECTRONS than PROTONS

Multiple Choice

How many protons?

• 36

• 17

• 18

• 19

Multiple Choice

How many neutrons?

• 36

• 17

• 18

• 19

Multiple Choice

How many electrons?

• 36

• 17

• 18

• 19

Multiple Choice

How many protons?

• 9

• 4

• 5

• 2

Multiple Choice

How many neutrons?

• 9

• 4

• 5

• 2

Multiple Choice

How many electrons?

• 9

• 4

• 5

• 2