Subatomic Particles in an atom!Subatomic Particles in an atom!

• 3 main particles in the atom:• Neutrons• Protons• Electrons

In physics, we will learn that even these particles are made of smaller particles!

p+

n

e-

SIZE

LOCATION

Remember, most of an atom is empty space!

Remember, most of an atom is empty space!

• An atomic model the size of Busch Stadium and parking would contain a pea sized nucleus containing 95.95% of the atoms mass.

• The pea at the pitcher’s mound would be the nucleus, and an ant crawling on the parking lot outside would be an electron!

ElectronsElectrons

• JJ Thompson, RA Millikan• Located around nucleus• Negatively (-) charged particles• Mass = essentially zero - only 1/2000 of a

proton or neutron• Charge = -1• Occupies the majority of space in an atom

e-

ProtonsProtons

• Eugen Goldstein (1886)• Located in….• The tiny, dense nucleus!• Mass of 1.67 x 10-24 grams• We call that 1 amu, or a mass of 1• Charge = +1

p+

NeutronsNeutrons

• James Chadwick (1932)

• Located in….• The tiny, dense nucleus!• Mass of 1.67 x 10-24 grams• We call that 1 amu, or a mass of 1• Charge = 0

n

Nuclear SymbolsNuclear Symbols

X = element symbol

Z = mass number

= # protons + # neutrons

A = atomic number

= # protons

(gives an element its identity!!)

So… # neutrons = Z-A

XZ

A

charge

Atomic NumberAtomic Number

• Number of protons• Number on bottom of symbol• Gives an atom its identity!• If 6 p+ in nucleus, the atom is….• Carbon!• It 7 p+ in nucleus, the atom is….• Nitrogen!

12

6 C

7

14

N

• Henry Moseley, and English scientist, bombarded atoms of elements with high speed cathode rays (electrons!)

• He found that the atoms gave off X-rays • He found that there was a pattern between

the amount of X-rays given off and the element that gave them off!He theorized that the nucleus of an atom was causing these X-rays to be given off

• The more protons in the nucleus, the more x-rays that were given off!

• He determined from this exactly how many protons were in the nucleus of each element!

• He called the number of protons the atomic number, and he said that this gave an element its identity!

• He rearranged the periodic table according to atomic number, and not according to atomic mass!

• This cleared up any irregular patterns that were found in the periodic table from before!

How was the atomic number of an element determined?How was the atomic number of an element determined?

• He was a physics professor at Oxford University!

• Henry Moseley did most of his experimentation when he was only 27 years old!

• Unfortunately, he died a year later, in 1915, during World War I. He was killed by a sniper in Turkey!

• His short career lasted less than four years…..

Moseley was a great scientist!Moseley was a great scientist!

Mass NumberMass Number

• Mass Number = number of protons + number of neutrons• Number on the top of the symbol• It tells you the mass of atom!• Not all atoms of the same element weigh the same!• Two atoms of Carbon are shown below. One weighs 12, one weighs 14.• If they are both Carbon, the must both have the same number of…..• Protons! Each has…..• 6 protons!• So different numbers of….• Neutrons!• How many neutrons

does each have? How would we figure that out?

• Mass Number - Atomic Number = Number of neutrons

14

6 C C12

66 neutrons! 8 neutrons!

ISOTOPESISOTOPES• Atoms with same # Protons, but different # neutrons• Example– 35Cl and 37Cl are isotopes of chlorine• They only differ in their…..• Mass!• They both have how many protons….?• 17!• Look at the periodic table, though - the periodic table lists the AVERAGE ATOMIC MASS• For chlorine, it is 35.453 amu. This doesn’t look like an average between 35 and 37!• That is because they don’t exist in nature 50-50!• Chlorine-35 makes up 75.77% of all Chlorine atoms in the universe• Chlorine-37 makes up 24.23% of all Chlorine atoms in the universe

ISOTOPES - again….ISOTOPES - again….

• How do we calculate the average atomic mass?

• Take each atom’s mass number, and multiply by the RELATIVE ABUNDANCE (That is what percentage it is in the universe)

• You must convert the relative abundance to a decimal

Example:

(35 amu)(.7577) + (37 amu)(.2423) =

35.4846 amu

• This is called a weighted average - because you don’t just add and divide by two!

Electrons and atom chargeElectrons and atom charge

• If # p+ = # e-

• Then atom is NOT CHARGED

• Charge = #p+ - #e-

• If #p > #e-• Then + charged

(cation)

• If # p < # e-• Then – charged

(anion)•ALL ELEMENTS ARE NEUTRAL, AND NOT CHARGED - AN ELEMENT HAS TO REACT IN ORDER TO BE CHARGED!

•A CHARGED ATOM IS CALLED AN ION

How many p+, n, e- ??How many p+, n, e- ??

108

47 Ag

20

Ca+2

41

p+ =

e- =

n =

Charge on atom….

p+ =

e- =

n =

Charge on atom….

47

47

61

20

18

21

0 +2

Write the nuclear symbol for…Write the nuclear symbol for…

• An atom containing 18 e-, 16 P, and 17 N.

• What element is it??• Atomic number = 16 • # p+ = 16• Element is….• Sulfur• Number of electrons tells us…• There are two more electrons

than protons• The electrons are winning by

2!• Charge is -2!• Mass Number = #p+ + #n

S33 -2

16

Which of the following represent isotopes of the same element?

Which of the following represent isotopes of the same element?

168X 16

7X 147X 14

6X 126X

Look for same atomic #: (same # protons)16

7X and 147X both have 7 protons, so are

isotopes of Nitrogen.14

6X and 126X both have 6 protons, so are

isotopes of C.