Chapter 4 – Atomic Structure Atom Atom - Greek for “Atomon” means“Indivisible” - Smallest...

Chapter 4 – Atomic StructureChapter 4 – Atomic Structure

AtomAtom - Greek for “Atomon” means“Indivisible”- Smallest unit that can exist alone

or in combination with other atoms.

Structure of an Atom … Things we know

Two main areas of the atom:

Nucleus

Electron cloud

Nucleus - contains protons (+) and neutrons (0)- dense, small

Electron cloud - contains electrons (-)- surrounds nucleus, mostly empty space- arranged in shells or energy levels

Nucleus - contains protons (+) and neutrons (0)- dense, small

Electron cloud - contains electrons (-)- surrounds nucleus, mostly empty space- arranged in shells or energy levels

Atom itself is neutral: Why? Number of p+ = e- n0 are neutral - no effect

Ions- atoms or molecules in which the total number of electrons does NOT equal the total number of protons. These particles have a CHARGE.

Cations- positive ions (lose electrons)

Anions- negative ions (gain electrons)

– atoms of the same element with different masses due to a different number of n0

Isotopes

Ex. H has 3 isotopes

1 p+ 1 p+

2 n01 e- 1 e- 1 e-1 e-

The only thing that changes is the neutrons… …so it is still hydrogen and acts like hydrogen but it is a little heavier with each additional neutron added…

H H H1 11

What if you change the number of neutrons? electrons?

Atom is very, very small overall→ we measure it in Angstroms 1 A = 1 x 10-10 m

More on Structure of an Atom … Things we know…

Atom is very, very small overall→ we measure it in Angstroms 1 A = 1 x 10-10 m

Nucleus is extremely tiny compared to the electron cloud.

Compare size of electron cloud to nucleus

How much smaller?????

Atom is very, very small overall→ we measure it in Angstroms 1 A = 1 x 10-10 m (compare to Metric

system units)

Nucleus “marble”

Electron Cloud “football field”

Nucleus is extremely tiny compared to the electron cloud.

Compare size of electron cloud to nucleus

Nucleus is a marble in the middle of a football stadium.

How much smaller?????

10 mill A = 1 mm

Compare size of proton, neutron, and electron

Proton’s mass = 1 amu

Neutron’s mass = 1 amu

Nucleus

NucleusElectron’s mass = 0 amu

Electron Cloud

Interesting Stuff … all the mass of the atom is in the nucleus…Wow! What does that mean about the density of the nucleus?

Electron Cloud

Interesting Stuff … all the mass of the atom is in the nucleus…Wow! What does that mean about the density of the nucleus?

1 amu (atomic mass unit) = 1.673 x 10-24 g

0.000000000000000000000001673 g

The atomic mass unit is easier to use to describe something so ridiculously small!

Does an electron having “0” amu means it weighs nothing?

Not Exactly … It’s just it is so small it does not matter relatively …

A word about the …

*amu – atomic mass unit – special unit for the mass of an atom. 1/12 mass of carbon-12 atom.

(relative to atom)

A word about the …

*amu – atomic mass unit – special unit for the mass of an atom. 1/12 mass of carbon-12 atom.

(relative to atom)

Similar to: 2000 lbs. = 1 ton

Easier to say 10 tons than 20,000 lbs.

Just like: 1 amu (atomic mass unit) = 1.673 x 10-24 g

Easier to say 2 amu than 2.346 x 10-24 g

How did we figure out all this stuff about the atom??? Because the atom is so small !!!!!

Before I start into the history……a little bit about Indirect Evidence???

Where to hunt?

Measure thickness of paper or a dollar?

The idea of the atom stems back to 400 BC by a Greek thinker named Democritus

…he called matter “atomon” meaning “indivisible”

400 BC

DemocritusDemocritus

The idea of the atom stems back to 400 BC by this Greek thinker

…he called matter “atomon” meaning “indivisible”

Now, this guy did not have any proof…he just thought about it and told people what he thought …

…Good Guess??400 BC

DemocritusDemocritus

Antoine LavoisierAntoine Lavoisier

Law of conservation of mass matter cannot be created nor destroyed

Joseph Proust Joseph Proust

Law of definite proportions a chemical compound contains the same elements in exactly the same proportions by mass

For this compound to be water… it must have exactly 2 H and 1 O

two H’s one O

What is this? H2O2

John Dalton John Dalton

Law of multiple proportions If compounds are composed of the same elements, the masses of the elements can be expressed as ratios of small whole #’s.

Carbon monoxide CO C = 12 g O = 16 g

Carbon dioxide CO2 C = 12 g O = 32 g

Ratio 1 : 1

Ratio 1 : 2Same elements but different ratios make different compounds

The Atomic TheoryThe Atomic Theory1. All matter is composed of extremely small, indivisible particles,

called atoms.2. Atoms of the same element are chemically alike. Atoms of

different elements are chemically different. .3. Atoms combine in whole # ratios to form compounds.4. Atoms are combined, separated, or rearranged in chemical

reactions.

John Dalton John Dalton

Joseph ThompsonJoseph Thompson

1897 Used a cathod ray tube to prove there were negative charged particles (now known as electrons) in an atom. This opened the way to the idea that an atom was not just a solid sphere not able to be broken down anymore.

Earnest RutherfordEarnest Rutherford In the gold foil experiment, he proved that the electron cloud was huge in volume comparison to the nucleus and the nucleus was extremely dense.

Neils BohrNeils Bohr

He proposed a model of the atom that showed that e- circled that nucleus of an atom in only allowed orbits or paths.

Dalton Model

1803 – John Dalton believed that an atom was an indestructible particle with no internal frame.

(Billiard Ball Model)

Thomson Model

1897 – J.J. Thomson discovers the electron. He believed electrons were embedded in positive charge sphere.

(Plum pudding Model)

Rutherford Model

1911 – Ernest Rutherford discovers that there is a dense, positively charged nucleus. Electrons go around the nucleus.

Bohr Model

1913 – Niels Bohr enhances Rutherford’s model by having electrons move in a circular orbit at fixed distances from the nucleus.

The Evolving Atomic Model Summary

Atomic Number – number of p+ in the nucleus of an atom (always equal to number of e-)

Mass Number – number of p+ and n0 in the

nucleus of an atom

Atomic Weight (mass) – the average mass of the isotopes

The mass number is just the atomic weight rounded off to a whole number!!

Atomic #

Mass # (rounded)

Atomic Weight

(# of p+ or e-)-

Mass # - Atomic # = n0

Shorthand method:

32.065

Put light blue boxes on your periodic table…as a reference

Atomic Weight = (Avg. mass of isotopes) = 32.066

Atomic # = (number of protons or electrons) = 16

Mass # = (Atomic weight rounded) = 32

# p+ = (same as Atomic #) = 16 p+

# e - = (same as Atomic #) = 16 e -

# n0 = (Mass # - Atomic #) = 16 n0 (32 – 16)

Try Sodium (Na):

Atomic Weight = (Avg. mass of isotopes) = ________

Atomic # = (number of protons) = ________

Mass # = (Atomic weight rounded) = ________

# p+ = (same as Atomic #) = ________

# e - = (same as Atomic #) = ________

# n0 = (Mass # - Atomic #) = ________

Atomic Weight = (Avg. mass of isotopes) = 32.066

Atomic # = (number of protons or electrons) = 16

Mass # = (Atomic weight rounded) = 32

# p+ = (same as Atomic #) = 16 p+

# e - = (same as Atomic #) = 16 e -

# n0 = (Mass # - Atomic #) = 16 n0 (32 – 16)

Try Sodium (Na):

Atomic Weight = (Avg. mass of isotopes) = ________

Atomic # = (number of protons) = ________

Mass # = (Atomic weight rounded) = ________

# p+ = (same as Atomic #) = ________

# e - = (same as Atomic #) = ________

# n0 = (Mass # - Atomic #) = ________22.991123111112

Atomic Weight = (Avg. mass of isotopes) = _______________

Atomic # = (number of protons) = ______________

Mass # = (Atomic weight rounded) = ______________

# p+ = (same as Atomic #) = ______________

# e - = (same as Atomic #) = ______________

# n0 = (Mass # - Atomic #) = ______________

Au Ag Pb

PRACTICE THESE…………

Atomic Weight = (Avg. mass of isotopes) = __________________

Atomic # = (number of protons) = __________________

Mass # = (Atomic weight rounded) = __________________

# p+ = (same as Atomic #) = __________________

# e - = (same as Atomic #) = __________________

# n0 = (Mass # - Atomic #) = __________________

Au Ag Pb

PRACTICE THESE…………

107.87

196.97

Shorthand Notation

Mass #

Atomic #

Ions- atoms or molecules in which the total number of electrons does NOT equal the total number of protons. These particles have a CHARGE.

Cations- positive ions (lose electrons)

Anions- negative ions (gain electrons)

Periodic Table Horizontal Rows are periods.

Indicate how many shells are needed to hold all of the electrons

Vertical columns are Groups or families Indicate the # of valence electrons 1 2 3 4 5 6 7 8

1 2 3 4 5 6 7 8

Ions Ions Metals

Lose Valence electrons Form Positive Ions

Equal to Group # Cations

NonMetals Gain electrons until they have 8*Form negative ions

Equal to how many electrons they gained

Anions

**Helium has 2 valence e-

*Silver has 1 valence e-

1 2 3 4 5 6 7 8

Ions Ions Metals (regular name)

Calcium Ion

NonMetals (end in “ide”)

Fluoride

– atoms of the same element with different masses due to a different number of n0

Isotopes

Ex. H has 3 isotopes

1 p+ 1 p+

2 n01 e- 1 e- 1 e-1 e-

The only thing that changes is the neutrons… …so it is still hydrogen and acts like hydrogen but it is a little heavier with each additional neutron added…

H H H1 11

If you change the number of neutrons…it is still Carbon but it makes a different isotope.

Different number of neutrons

Carbon –12 Carbon - 14

Isotopes? Isotopes?

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

What is an Average Atomic Mass (weight)?

8 p+ 8 p+

10 n08 e- 8 e- 1 e-8 e-

O O O8 88

17 1816

It comes from the isotopes…Let’s look at Oxygen…Look at our periodic table…why the decimals????

Oxygen 16 Oxygen 17 Oxygen 18(15.994915)(0.99762) + (16.999131)(0.00038) + (17.999160)(0.0020)

= 15.9994 average atomic mass

Almost all of Oxygen is Oxygen 16 but there are small amounts of the others…therefore it makes sense that the average atomic mass would be closest to 16…here is how it is figured …

99.762% 0.038% .20%

Isotope Calculations

(abundance as a decimal) ( mass of

isotope)

+ (abundance as a decimal) ( mass of

isotope)

+ (abundance as a decimal) ( mass of

isotope) Answer =

Isotope Calculations

Element X has two natural isotopes. The isotope with a mass of 10.012 amu has a relative abundance of 19.91%. The isotope with a mass of 11.009 amu has a relative abundance of 80.09%.

10.810 amu

Answer =

Lewis Dot Structures1) Find your element on the

periodic table.2) Determine the number of

valence electrons.3) This is how many electrons

you will draw

Lewis Dot Structures1) Write the element symbol.2) Write down the number of

valence electrons (based of the group #)

3) Write down the symbol and draw an imaginary box around it

4) Draw the valence electrons as dots on the sides of the box.

One at a time on each side until you are out of valence electrons

Lewis Dot StructuresOn an open area on your notes, try these elements on your own:

1) H2) P3) Ca4) Ar5) Cl6) Al

Bohr Model of the AtomBohr Model of the Atom – …Kinda like concert seating!

Put the number of p+ , n0 , and e- in the diagram as shown…Lets diagram Sulfur

p+ = Atomic # = 16

e- = Atomic # = 16

n0 = Mass # - Atomic # = 32 – 16 = 16

Remember that mass # is atomic weight rounded

p+ = 16

n0 = 16e- = 2 e- = 8e- = 2 e- = 2e- = 6 e- =

Maximum seats = 2 8 18 32

Bohr Model of the AtomBohr Model of the Atom – …Kinda like concert seating!

Put the number of p+ , n0 , and e- in the diagram as shown…Lets diagram Sulfur

p+ = Atomic # = 16

e- = Atomic # = 16

n0 = Mass # - Atomic # = 32 – 16 = 16

Remember that mass # is atomic weight rounded

p+ = 16

n0 = 16e- = 2 e- = 8e- = 2 e- = 2e- = 6 e- =

Maximum seats = 2 8 18 32 2n2

n = shell number1 2 3 4

*NOT ACTUAL MODEL*

Bohr Model of the AtomBohr Model of the Atom – Try these…

p+ = ?

n0 = ?e- = 2 e- = 8e- = 2 e- = 2e- = 6 e- =

Maximum seats = 2 8 18 32 2n2

n = shell number1 2 3 4

LithiumLithium MagnesiumMagnesium

HeliumHelium ArgonArgon

Chapter 4 – Atomic Structure Atom Atom - Greek for “Atomon” means“Indivisible” - Smallest...

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