Atoms and their Structure

Protons-positiveElectrons-negative

Neutrons-no charge (neutral)

Models of the Atom

Bohr model-compared electrons to planets

•Because science is always changing, we realized that Bohr’s model could not explain all of our observations!!

Electrons are found in orbitals-behave like waves-quantum theory!There are four kinds of orbitals:

s orbitalsp orbitalsd orbitalsf orbitals

Each orbital has a different amount of energy

Orbitals closer to the nucleus have less energy than orbitals further from the nucleus

Valence ElectronsElectrons that are found in the outermost energy level of an atom

How do we know how many valence electrons a particular atom has???

The first orbital can hold 2 electrons

The second and third orbitals can each hold 8 electrons

Higher orbitals are more complicated and will be learned in Chemistry class!

How many valence electrons would an electrically neutral Carbon atom have???

Carbon has 6 protons, therefore an electrically neutral atom would need 6 electrons to balance the charge

Carbon’s first orbital can only have 2 electrons

6 total electrons – 2 first shell electrons leaves 4 electrons in the outer shell (valence shell)

A Tour of the Periodic Table

Periodic Law says:

1) Properties of elements tend to change according to a regular pattern when those elements are arranged by increasing atomic number!!

What does this mean???

It means that elements with certain characteristics in common (like # of valence electrons) are more likely to have similar chemical properties (like what kinds of atoms they react with!)

Periods and GroupsHorizontal Rows (left-

right) are called PERIODS

Handy for determining valence shell electrons!!

Periods and GroupsVertical columns (up-down)

are called GROUPS

All elements in a particular group will have the same number of valence electrons, which gives them all similar chemical properties

Atoms that have lost or gained electrons are called…IONS

Atoms that have lost or gained neutrons are called…ISOTOPES

Cation=atom that has lost electrons, giving it a positive charge

i.e. Li+

Anion=atom that has gained electrons, giving it a negative charge

i.e. Cl-

Metals-most elements are metals

-good conductors of heat and electricity

-most are fairly reactive

Metals continuedAlkali Metals-found in Group 1-Highly reactive-one valence electron-readily form cations (+)-not found naturally in nature-why?

Alkaline Earth Metals-Found in Group 2

-Very reactive, but not as reactive as Alkali Metals

-2 valence electrons

-readily form cations (+2)

-too reactive to be found alone in nature

TRANSITION METALSGroups 3-12

Can form more than one cation, depending on what they are bonding with

Very useful in technology and economy

NonmetalsFound on the right side of the

periodic table

Very plentiful on earth-especially carbon, silicon, oxygen,

nitrogen, and sulfur

Readily form anions by gaining electrons to form full outer

shells

Halogens-elements in Group 17

-very reactive, especially with alkali metals!

-7 valence electrons-only need ?? To have a full shell…

-form anions (-1) by GAINING that one missing electron

Noble Gases-Group 18-Found in Group 18

-all inert gases

-full valence shells-do not need to get any more electrons, therefore they do not react with other atoms or elements-will not form ions

SemiconductorsFound on the “stairsteps”

Intermediate conductors of heat and electricity-not as good as metals, but better than nonmetals

Classified as nonmetals, but have some properties of metals-sometimes called “metalloids”

Using Moles to Count Atoms

The mole is a counting unit, much like “dozen” or “pair”

A dozen = 12 objectsA pair = 2 objectsA mole = 6.022 x 1023 objects

6.022 x 1023 is known as Avogadro's constant

Molar MassAverage atomic mass is the mass of 1

atom

Molar mass is the mass of 1 mole of atoms

The number is the same for both of these and can be found on the periodic table, usually under the Chemical symbol for that particular element

The only difference for these two values is the unit you use -Atomic Mass Unit vs grams/mole

Conversion FactorsJust as we used a conversion factor to

do our metric conversions, we will use a conversion factor to go from

moles → mass

and mass → moles

More Conversion FactorsFor our purposes, the conversion factor

is the molar mass of an element-found on the periodic table

So...

1 mole Carbon = 12.011 grams

12.011 grams Carbon = 1 mole