DETERMINE THE NUMBER

OF PROTONS, NEUTRONS AND ELECTRONS IN AN

ATOM

Counting the Pieces Atomic Number = number of

protons # of protons determines kind of

atom. the same as the number of

electrons in the neutral atom.

Counting the Pieces Mass Number = the number of

protons + neutrons.

All the things with mass.

NOT on the periodic table

Isotopes Atoms of the same element can

have different numbers of neutrons.

different mass numbers. called isotopes.

Writing Isotopes Two ways: Hyphen notation

–Name of element – mass number Ex:

–carbon- 12–carbon -14–uranium-235

Nuclear Symbol Notation Contain the symbol of the element, the

mass number and the atomic number.

X Massnumber

Atomicnumber

Symbols Find the

–number of protons–number of neutrons–number of electrons–Atomic number–Mass Number–Name

Na2411

Symbols Find the

–number of protons = 11 –number of neutrons = 13–number of electrons = 11–Atomic number = 11–Mass Number = 24–Name = sodium – 24

Na2411

Symbols Find the

–number of protons–number of neutrons–number of electrons–Atomic number–Mass Number–Name

Br80 35

Symbols Find the

–number of protons = 35–number of neutrons = 45–number of electrons = 35–Atomic number = 35–Mass Number = 80–Name = bromine - 80

Br80 35

Symbols if an element has an atomic

number of 34 and a mass number of 78 what is the –number of protons–number of neutrons–number of electrons–symbol–Name

ANSWERS if an element has an atomic

number of 34 and a mass number of 78 what is the –number of protons = 34–number of neutrons = 44–number of electrons = 34 –Name = selenium – 78

78

34Se

Symbols if an element has 91 protons and

140 neutrons what is the –Atomic number–Mass number–number of electrons–Name–symbol

ANSWERS if an element has 91

protons and 140 neutrons what is the –Atomic number = 91–Mass number = 140–number of electrons = 91–Name = Protactinium - 140

Pa140

91

Average Atomic Mass A weighted average of all naturally occuring

isotopes of an element. There is a formula used to calculate average

atomic mass: = (mass of isotope 1) (% abundance/100)

(mass of isotope 2) (%abundance/100)

+...________________________________

Unit for Atomic Mass The atomic mass unit (amu) amu definition - one twelfth the

mass of a carbon-12 atom. Each isotope has its own atomic

mass relative to the carbon-12 atom

Atomic Mass You try…

Calculate the atomic mass of copper if copper has two isotopes. 69.1% has a mass of 62.93 amu and 30.9% has a mass of 64.93 amu.

Answer

(62.93 amu) (69.1% / 100) = 43.48 amu

+(64.93 amu) (30.9% / 100) = 20.06 amu

63.54 amu

Atomic Mass Magnesium has three isotopes. 78.99%

magnesium-24 with a mass of 23.9850 amu, 10.00% magnesium-25 with a mass of 24.9858 amu, and 11.01% magnesium-25 with a mass of 25.9826 amu. What is the atomic mass of magnesium?

Answer(23.9850 amu) (78.99% / 100) = 18.9457

(24.9858 amu) (10.00% / 100) = 2.49858

(25.9826 amu) (11.01% / 100) = 2.86068

24.304 amu

Atomic Mass Is not a whole number because it is an

average. are the decimal numbers on the periodic

table.