Atomic Structure

AtomAtom ElementElement

MoleculeMolecule CompoundCompound

The Basic Analogy

Element-Cannot be broken down into another substanceIs made up of only one type of atom

Properties of theElements

Properties of theCompound

Hydrogen?

Oxygen?

Water?

Molecules & Compounds

Analogy: It’s like putting two lego blocks together and gettinga Cow! (but there are reasons why this happens)

So…What’s in an Atom?

Particle Location Charge Mass

Proton Nucleus +1 1 amu

Neutron Nucleus 0 1 amu

Electron Orbitals -1 0 amu

AnATOMy of An ATOM

Electron

Nucleus withProtons & Neutrons

Some Typical Atoms

Hydrogen

1P+

1e-

Carbon

6P+6N

6e-

Rules for Atoms

• The Net Charge for any atom should equal … 0

• This means that there should be the same number of Protons and Electrons!

• The number of PROTONS defines the element (This is the Atomic Number)

More About Atoms

• The MASS NUMBER of an atom is the sum of the number of PROTONS and the number of NEUTRONS.

What happens if...

• An atom gains or loses electrons?– you get an ION…a charged particle

• An atom gains or loses neutrons?– you get an ISOTOPE…a heavier or lighter

form of the same substance

• An atom gains or loses protons?– you get a different element (happens in nuclear

fission or fusion)

Atomic Mass (not Mass Number)

• Definition: the weighted average of all of the isotopes of an element.

• What’s a weighted average?– Take carbon for example. You’ll notice that the

atomic mass is very close to 12. There are heavier forms of carbon, but they occur much less frequently than Carbon 12. If you take the average based on how frequently they occur, the relative amount of Carbon 12 brings the average close to 12.

More History (Yippeeee!)

Ernie’s (Rutherford) Big AdventureErnie’s (Rutherford) Big Adventure

Thin Sheet of GoldAtoms

Rutherford’s Conclusion

• Atoms are made of mostly EMPTY SPACE!– Actually, the ratio of the size

of the nucleus to the diameter of the orbits of electrons can be compared with placing a marble in the middle of a football stadium!

Constructing Atoms…

• An atom has an atomic number of “6”, and a mass number of “14”. – Sketch the Atom

• Use the 2-8-8…rule for electron orbitals

– Identify the Element (Periodic Table)– Is the atom the most common form for the element?

• An atom has an atomic number of “14”. Sketch its most common form!

Periodic Table

H He

Li Be B C N O F Ne

Na Mg Al Si P S Cl Ar

H He

Li Be B C N O F Ne

Na Mg Al Si P S Cl Ar

Group

sG

roups

PeriodsPeriods

Group...• Within a Group or Family

– Same number of electrons in outer level– React similarly– Are likely to form similar Ions

• Moving Down a Group– Add one electron shell each time– Elements on the left (Group 1) get more reactive as you go

down a column.– Elements on the right (Group 7) get less reactive as you go

down a column.

Periods...

• Elements in the same period…– Have the same number of energy levels

• As you go across a period…– Atomic number increases by “1”– One electron is added to the outer shell each time– Change in reactivity– Form different types of Ions