The Structure of the Atom

The Building Block of Matter

Atoms are the smallest particles of an element that retains the chemical properties of that element Parts:

Nucleus – small region in the center of the atom. (+ charged protons, = charged neutrons)

Electron Cloud – large region, compared to nucleus, where electrons are found.

Size of nucleus vs. electron cloudIf an atom was the size of a sports stadium, the

nucleus would be the size of a marble!Subatomic Particles: Protons : + charge, relative mass = 1.007 atomic mass

units (amu); round to 1 Neutrons: = charge, relative mass = 1.009 atomic mass

units (amu); round to 1 Electrons: - charge, relative mass = 0.0005 atomic mass

units (amu); round to 0 (not factored in when figuring total mass of an atom)

Structure of Subatomic Particles Subatomic particles composed of fast moving

points of energy called quarksQuark Calculations

(for protons and neutrons)Each proton is 2 up quarks and 1 down quark

2(2/3) – 1(1/3) = 4/3 – 1/3 = 3/3 or +1Each neutron is 2 down quarks and 1 up quark

2(-1/3) + 2/3 = 0Each electron is composed of 2 down quarks

3(-1/3) = -1

Atomic Number

Number of protons in the nucleus (also the number of electrons)

Typically the number on top of the symbol on the Periodic Table.

AlAl 13

26.981

Atomic Number

Mass Number

Number of protons + number of neutrons in an atom.

When solving for number of neutrons: round mass number properly, subtract atomic number from mass number.

Element Symbols

Hyphen Notation:Element symbol – Mass # (rounded)Example: Helium He-4

Nuclear Symbol:Superscript Mass Number, Subscript

Atomic Number, SymbolExample:

He42

IONS IONS IONSIONS are atoms or groups of atoms with a positive or are atoms or groups of atoms with a positive or

negative charge. negative charge. Taking awayTaking away an electron from an atom gives a an electron from an atom gives a CATIONCATION

with a with a positive chargepositive charge AddingAdding an electron to an atom gives an an electron to an atom gives an ANIONANION with a with a

negative chargenegative charge.. To tell the difference between an atom and an ion, look To tell the difference between an atom and an ion, look

to see if there is a charge in the superscript! Examples: to see if there is a charge in the superscript! Examples: NaNa++ Ca Ca+2+2 I I-- O O-2-2

Na Ca I ONa Ca I O

Forming Cations & AnionsForming Cations & Anions

A A CATIONCATION forms forms when an when an atom atom losesloses one or more one or more electrons.electrons.

An An ANIONANION forms forms when an when an atom atom gainsgains one or more one or more electronselectrons

Mg --> Mg2+ + 2 e- F + e- --> F-

Isotopes

Atoms with the same number of protons & electrons but a different number of neutrons.

They are the same element, but have different masses. (different mass number)

All isotopes are used to calculate atomic mass (reason why weight is a decimal).

Most elements consist of a mixture of isotopes.

Average Average Atomic Atomic MassMass

Because of the existence of isotopes, the mass of Because of the existence of isotopes, the mass of a collection of atoms has an average value.a collection of atoms has an average value.

Boron is 20% Boron is 20% 1010B and 80% B and 80% 1111B. That is, B. That is, 1111B is 80 B is 80 percent abundant on earth. percent abundant on earth.

For boron average atomic massFor boron average atomic mass = 0.20 (10 amu) + 0.80 (11 amu) = 10.8 amu= 0.20 (10 amu) + 0.80 (11 amu) = 10.8 amu

10B

11B

How to determine Average Atomic Mass1. Determine Relative Abundance –

% abundance divided by 1002. Determine weight of each isotope –

multiply relative abundance by mass (keep all digits calculator gives you, no rounding yet)

3. Determine Average Atomic Mass - add up all individual weights, round to “2” decimal places

How to determine Percent Abundance Use the following equation:Ave. Atomic Mass = (X)(Mass of 1st isotope)+(1-X)(Mass of 2nd isotope)

1. Solve for “X”2. Answer will be a decimal3. To solve for other isotope, do 1 – answer4. Multiply both answers by 1005. Two answer should equal 100

Let’s see what you learned…

Get your clickers ready!!!

Which two subatomic particles are found in the nucleus of an atom?

Proton / E

lect...

Proton / N

eutr...

Electr

on / Neu...

Proton / Q

uark

Neutron / Q

uar...

20% 20% 20%20%20%

1. Proton / Electron2. Proton / Neutron3. Electron / Neutron4. Proton / Quark5. Neutron / Quark

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30

The atomic number represents the number of …

Protons

Neutrons

Protons +

Neut...

Protons +

Elec...

25% 25%25%25%

1. Protons2. Neutrons3. Protons + Neutrons4. Protons + Electrons

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30

The mass number represents the number of …

Electr

ons

Protons +

Elec...

Protons +

Neut...

Neutrons +

Ele...

25% 25%25%25%1. Electrons2. Protons + Electrons3. Protons + Neutrons4. Neutrons + Electrons

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30

What is the correct Hyphen Notation for Calcium

Ca – 20

Ca – 40.078

Ca – 40.08

Ca – 40.1

Ca - 40

20% 20% 20%20%20%

1. Ca – 202. Ca – 40.0783. Ca – 40.084. Ca – 40.15. Ca - 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

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An atom has 14 protons and 20 neutrons. The element is …

Si Ca Se C

25% 25%25%25%1. Si2. Ca3. Se4. C

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30

An atom has 15 protons and 17 neutrons. What element is it?

Cl He Ge P

25% 25%25%25%1. Cl2. He3. Ge4. P

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30