The Atom & Subatomic Particles

Atomic NumberAtomic Number

atomic number:atomic number: = size of nuclear charge= size of nuclear charge = number of protons in nucleus= number of protons in nucleus determines identity of elementdetermines identity of element used to give order to periodic tableused to give order to periodic table

For neutral atoms:For neutral atoms: atomic number = number of electronsatomic number = number of electrons

What is an atom?

Number of Protons = Number of ElectronsNumber of Protons = Atomic NumberAtomic Mass = Protons + Neutrons

What we knew by 1932:What we knew by 1932:

1.0087 amu1.0087 amu

(or 1 amu)(or 1 amu)

00Neutron, Neutron, 11nn

1.0073 amu1.0073 amu

(or 1 amu)(or 1 amu)

+1+1Proton, Proton, 11p or p or 11HH

.0005486 amu.0005486 amu

(or 0 amu)(or 0 amu)

-1-1Electron, Electron, 00ee

Relative MassRelative MassRelative ChargeRelative Charge

-1-1

11 11

00

Location of Subatomic ParticlesLocation of Subatomic Particles

• Electrons located Electrons located outsideoutside nucleus nucleus

• Protons & neutrons located Protons & neutrons located insideinside nucleus nucleus

• Protons & neutrons = nucleonsProtons & neutrons = nucleons

IsotopesIsotopes

atoms of same element with atoms of same element with

different # neutronsdifferent # neutrons (mass # is different) (mass # is different) # protons stays same! (atomic # is same)# protons stays same! (atomic # is same)

DaltonDalton’’s theory modified in number of s theory modified in number of important ways:important ways: the atom is divisible (the atom is divisible (protons, neutrons, electrons)protons, neutrons, electrons) atoms of same element can be different (atoms of same element can be different (different different

# neutrons# neutrons))

Mass NumberMass Number

Mass number = # protons + # neutronsMass number = # protons + # neutrons

NotationNotation

1212CC66

•left left superscriptsuperscript is is mass numbermass number

•left left subscriptsubscript is is atomic numberatomic number

NotationNotation

1212CC66

12 = # protons + neutrons12 = # protons + neutrons 6 = # protons6 = # protons

12 – 6 = 6 neutrons12 – 6 = 6 neutrons

How many neutrons in this How many neutrons in this atom?atom?

1717OO88

Mass number is ?Mass number is ?

Atomic number is ?Atomic number is ?

# of neutrons is ?# of neutrons is ?

# of electrons in atom is?# of electrons in atom is?

1717

88

17 – 8 = 917 – 8 = 9

88

Mass number is ?Mass number is ?

Atomic number is ?Atomic number is ?

# of neutrons is ?# of neutrons is ?

# of electrons in atom is?# of electrons in atom is?

1515

NN77

1515

77

15 – 7 = 815 – 7 = 8

77

Mass number is ?Mass number is ?

Atomic number is ?Atomic number is ?

# of neutrons is ?# of neutrons is ?

# of electrons in atom is?# of electrons in atom is?

19 19 FF

1919

99

19 – 9 = 1019 – 9 = 10

99

Other NotationsOther Notations Might also see: C-Might also see: C-1212

number following symbol is number following symbol is mass numbermass number!!

Need to look up atomic numberNeed to look up atomic number

WhatWhat’’s the difference between s the difference between H-1, H-2, and H-3H-1, H-2, and H-3??

All HAll H’’s have 1 protons have 1 proton

H-1: mass # = 1 H-1: mass # = 1 1 proton, 0 neutrons1 proton, 0 neutrons

H-2: mass # = 2 H-2: mass # = 2 1 proton, so it must have 1 neutron1 proton, so it must have 1 neutron

H-3: mass # = 3 H-3: mass # = 3 1 proton, so it must have 2 neutrons1 proton, so it must have 2 neutrons

Consider U-234, U-235, & U-238Consider U-234, U-235, & U-238

WhatWhat’’s the atomic number of U?s the atomic number of U? How many protons in U?How many protons in U? How many neutrons in U-234?How many neutrons in U-234? How many neutrons in U-235?How many neutrons in U-235? How many neutrons in U-238?How many neutrons in U-238? How many electrons in U?How many electrons in U?

9292

9292234 – 92 = 142234 – 92 = 142

235 – 92 = 143235 – 92 = 143

238 – 92 = 146238 – 92 = 146

9292

How many neutrons in Po-217?How many neutrons in Po-217?

WhatWhat’’s the atomic number?s the atomic number?

How many protons?How many protons?

So the neutrons are …So the neutrons are …

8484

8484

217 – 84 = 133 neutrons!217 – 84 = 133 neutrons!

IONSIONS

Atoms: electrically neutral so ...Atoms: electrically neutral so ...

# electrons = # protons# electrons = # protons IONS = atoms that gained or lost IONS = atoms that gained or lost electronselectrons protons and electrons aren't = anymore, so ions protons and electrons aren't = anymore, so ions

are are not not neutral they carry a charge (+/-)neutral they carry a charge (+/-)

IONSIONS

Charge of ion: = # protons minus # Charge of ion: = # protons minus # electrons electrons

(subtract the electrons since are negative)(subtract the electrons since are negative)

IONSIONS

If atom loses electrons, it has more If atom loses electrons, it has more positive charge than negative positive charge than negative What kind of ion is it?What kind of ion is it?

If atom gains electrons, it has more If atom gains electrons, it has more negative charge than positive negative charge than positive What kind of ion is it?What kind of ion is it?

positivepositive

negativenegative

Charge of IonsCharge of Ions

Ion chargeIon charge written as written as right superscriptright superscript ClCl-1-1 a chloride ion with a charge of -1a chloride ion with a charge of -1 NaNa+1+1 a sodium ion with a charge of +1a sodium ion with a charge of +1 OO-2-2 an oxygen ion with a charge of -2an oxygen ion with a charge of -2

If no right superscript, itIf no right superscript, it’’s understood to s understood to be zero and therefore a neutral atombe zero and therefore a neutral atom

Putting it all togetherPutting it all together

How many protons, neutrons, & electrons How many protons, neutrons, & electrons in each of the followingin each of the following

2323NaNa+1+1

11

2525MgMg+2+2

1212

3434SS-2-2

1616

6464ZnZn+2+2

3030

11 p, 12 n, 10 e11 p, 12 n, 10 e

12 p, 13 n, 10 e12 p, 13 n, 10 e

16 p, 18 n, 18 e16 p, 18 n, 18 e

30 p, 34 n, 28 e30 p, 34 n, 28 e

Lost Lost 11

Got 2Got 2

Lost Lost 22

Lost Lost 22

What is an amu?What is an amu?

equal to the atomic mass unitequal to the atomic mass unit

amu amu 1/12 the mass of the C-12 atom 1/12 the mass of the C-12 atom

C-12 is used as the reference for atomic massC-12 is used as the reference for atomic mass

Atomic Weight or MassAtomic Weight or Mass

Atomic mass is relativeAtomic mass is relative 11stst H-1 used as standard: H-1 used as standard:

1 atom of H = 1 amu1 atom of H = 1 amu next O-16 used as standard:next O-16 used as standard:

O combines with many elementsO combines with many elements 1 atom of O = 16 amu's1 atom of O = 16 amu's

Now C-12 is the standard:Now C-12 is the standard: 1 atom of C-12 has a mass of exactly 12 amu's1 atom of C-12 has a mass of exactly 12 amu's