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

• 3 main particles in the atom:3 main particles in the atom:• NeutronsNeutrons• ProtonsProtons• ElectronsElectrons

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

p+

n

e-

SIZESIZE

LOCATIONLOCATION

Remember, most of an atom is Remember, most of an atom is empty space!empty space!

Remember, most of an atom is Remember, most of an atom is empty space!empty space!

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

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

• That is how much empty That is how much empty space is in an atom, and how space is in an atom, and how tiny electrons are compared tiny electrons are compared to the nucleus!to the nucleus!

ElectronsElectronsElectronsElectrons

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

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

but contributes NOTHING to the mass of an but contributes NOTHING to the mass of an atom!atom!

e-

ProtonsProtonsProtonsProtons

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

p+

NeutronsNeutronsNeutronsNeutrons

• James Chadwick (1932)James Chadwick (1932)

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

n

Nuclear SymbolsNuclear SymbolsNuclear SymbolsNuclear Symbols

X = element symbolX = element symbol

Z = mass numberZ = mass number

= # protons + # = # protons + # neutronsneutrons

A = atomic number A = atomic number

= # protons= # protons

(gives an element its (gives an element its identity!!)identity!!)

So… # neutrons = Z-ASo… # neutrons = Z-A

XXZZ

AA

chargecharge

Atomic NumberAtomic NumberAtomic NumberAtomic Number

• Number of protonsNumber of protons• Number on bottom of symbolNumber on bottom of symbol• Gives an atom its identity!Gives an atom its identity!• If If 6 p6 p++ in nucleus, the atom is…. in nucleus, the atom is….• Carbon!Carbon!• It 7 pIt 7 p++ in nucleus, the atom is…. in nucleus, the atom is….• Nitrogen!Nitrogen!

1212

66 CC

77

1414

NN

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

does each have? How would does each have? How would we figure that out?we figure that out?

• Mass Number - Atomic Number = Mass Number - Atomic Number = Number of neutronsNumber of neutrons

1414

66 CC CC1212

666 neutrons!6 neutrons! 8 neutrons!8 neutrons!

ISOTOPESISOTOPESISOTOPESISOTOPES• Atoms with same # Protons, but different # neutronsAtoms with same # Protons, but different # neutrons• Example– Example– 3535Cl and Cl and 3737Cl are isotopes of chlorineCl are isotopes of chlorine• They only differ in their…..They only differ in their…..• Mass!Mass!• They both have how many protons….?They both have how many protons….?• 17!17!• Look at the periodic table, though - the periodic table lists the AVERAGE ATOMIC MASSLook 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!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!That is because they don’t exist in nature 50-50!• Chlorine-35 makes up 75.77% of all Chlorine atoms in the universeChlorine-35 makes up 75.77% of all Chlorine atoms in the universe• Chlorine-37 makes up 24.23% of all Chlorine atoms in the universeChlorine-37 makes up 24.23% of all Chlorine atoms in the universe

Electrons and atom chargeElectrons and atom chargeElectrons and atom chargeElectrons and atom charge• If # pIf # p++ = # e = # e--

• Then atom is NOT Then atom is NOT CHARGEDCHARGED

• Charge = #pCharge = #p++ - #e- - #e-

• If #p > #e-If #p > #e-• Then + charged Then + charged

(cation)(cation)

• If # p < # e-If # p < # e-• Then – chargedThen – charged

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

•A CHARGED ATOM IS CALLED AN IONA CHARGED ATOM IS CALLED AN ION

•A NEGATIVE ION IS CALLED AN ANION, AND A POSITIVE ION A NEGATIVE ION IS CALLED AN ANION, AND A POSITIVE ION IS CALLED A CATIONIS CALLED A CATION

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

108108

4747 AgAg

2020

CaCa+2+2

4141

pp+ + = =

ee- - = =

n = n =

Charge on atom….Charge on atom….

pp+ + = =

ee- - = =

n = n =

Charge on atom….Charge on atom….

4747

4747

6161

2020

1818

2121

00 +2+2

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

• An atom containing 18 e-, An atom containing 18 e-, 16 p16 p++, and 17 n., and 17 n.

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

than protonsthan protons• The electrons are winning by The electrons are winning by

2!2!• Charge is -2!Charge is -2!• Mass Number = #pMass Number = #p++ + #n + #n• 16 p16 p+ + + 17 n = mass of 33+ 17 n = mass of 33

SS3333 -2-2

1616

Which of the following represent Which of the following represent isotopes of the same element?isotopes of the same element?

Which of the following represent Which of the following represent isotopes of the same element?isotopes of the same element?

161688XX 1616

77XX 141477XX 1414

66XX 121266XX

Look for same atomic #: (same # of protons)Look for same atomic #: (same # of protons)1616

77XX and and 141477X both have 7 protons, so are X both have 7 protons, so are

isotopes of Nitrogen.isotopes of Nitrogen.1414

66XX and and 121266X both have 6 protons, so are X both have 6 protons, so are

isotopes of C. isotopes of C.

Which of the following represent Which of the following represent ions?ions?

Which of the following represent Which of the following represent ions?ions?

23231111XX +1+1 1414

77XX 191999XX-1-1

A charge atom is known as an IONA charge atom is known as an ION Positive ions are called CATIONSPositive ions are called CATIONS Negative ions are called ANIONS Negative ions are called ANIONS Look for any atom with charge in the upper right hand cornerLook for any atom with charge in the upper right hand corner

(with a + or -)(with a + or -) Charge means the atom has reacted, and now has either MORE electrons Charge means the atom has reacted, and now has either MORE electrons

than protons, or LESS electrons than protonsthan protons, or LESS electrons than protons Atoms with – charge have GAINED electronsAtoms with – charge have GAINED electrons Atoms with + charge have LOST electronsAtoms with + charge have LOST electrons