Atomic Structure & the Periodic

Table

AtomsAtom smallest particle that has the properties of an element

PROPERTIES

Democritus

Atoms are the building blocks of molecules

John Dalton’s Theory• every element is made of tiny, unique particles called atoms that cannot be subdivided• atoms of the same element are exactly alike• atoms of different elements can join to form molecules

What is an Atom?

Water

Three main Subatomic Particles

Nucleus the center of an atom; made up of protons & neutrons

Proton a positively charged subatomic particle in the nucleus of an atom

Neutron a neutral subatomic particle in the nucleus of an atom

Electron a tiny negatively charged subatomic particle moving around outside the nucleus of an atom

4 miles

Atoms have no overall charge?Atoms do not have a charge because they have an equal number

of protons & electrons whose charges exactly cancel.

Atomic ModelsBohr’s model

electrons in an atom move in set paths around the nucleus (like the planets orbiting the sun)

Energy level / shell any of the possible energies an electron may have in an atom

Atomic ModelsModern TheoryBohr’s model

It is impossible to determine both

the exact location of an electron (e- )

in an atom & its speed & direction

Visual method uses an… e- cloud

Shaded region used to demonstrate the possible location of an e-

Atomic Number Mass Number Isotopes

Model of Helium

What does an atom really look like?

The Electron Cloud Model is the current accepted model of the atom

This model illustrates the nucleus and the electrons in a cloud around the nucleus

Electron Orbitals• Electrons occupy the lowest energy levels available in an atom

• Within each energy level, e- occupy orbitals w/the lowest energy

• s, p, d, f – order of orbit strength (weakest to strongest)

Valence ElectronsValence electron Electron(s) in the outermost energy level of an atom

8e-

2e-

How do the structures of atoms differ?

Atomic number (Z) • the number of protons in the nucleus• Note: All atoms of the same element have the same atomic number/protons.• In a neutral atom the number of protons is equal to the number of electrons

Atomic Mass (A)

the total number of protons and neutrons in the nucleus of an atom

Because atomic masses are averages, many of them are decimals instead of whole #’s.

ISOTOPESDoes changing the number of neutrons affect the number of p+ & e- ?

Isotopes any atoms having the same number of protons but different numbers of neutrons

• have different mass #’s

Calculating neutrons

How many neutrons are in radioactive uranium-235?

Mass of an Atomatomic mass unit (amu) a quantity equal to one-twelfth of the mass

of a carbon-12 atom

average atomic mass the weighted average of the masses of all naturally occurring isotopes of an element

EX: Determine each of the following given this picture…

# e-

# p +

# n

Atomic #

Mass #

Element Name

Element Symbol

Now Complete the handout “I/S Atomic Structure Worksheet”…

Then, let’s go over the intro packet (first couple of pages…).

IONSAtoms of Group 1 elements are reactive, why?

• because their outermost energy levels are only partially filled

Ionization process of adding e- to or removing e- from an atom or group of atoms

Ion an atom or group of atoms that has lost or gained one or more e- and therefore has a net electric charge

Cation an ion w/a positive charge

Li Li ++

IONSAnion an ion w/a negative

charge

F F --

How do the structures of atoms differ?

Atomic number (Z) the number of protons in the nucleus

Mass number (A)the total number of protons and neutrons in the nucleus of an atom

Periodic Table• elements are represented by their symbols

• arranged by # of protons found in the nucleus

Periodic Law properties of elements tend to change in a regular pattern when elements are arranged in order of increasing atomic # (# of protons in their atoms)

Periodic TableDmitri Mendeleev

?

Mendeleev arranged the elements into rows in order of increasing mass so that elements w/similar

properties were in the same column

Why couldn’t Mendeleev make a complete periodic table?

Gallium

Periodic Table

Group (family)

a vertical column of elements in the periodic table

Period a horizontal row of elements in the periodic table

• the # of p+ & e- increase by one, moving from left to right

• group members have the same # of valence e-

• have similar properties

Element Families• elements are classified as either metals or nonmetals

Metals the elements that are good conductors of heat & electricity

Nonmetals the elements that are usually poor conductors of heat & electricity

Semiconductors the elements that are intermediate conductors of heat & electricity

Metals (4 types)

Alkali metals highly reactive metallic elements located in Group 1 of the periodic table

Are alkali metals often found in nature as

elements?

Alkaline-earth metals reactive metallic elements located in Group 2 of the periodic table

MetalsTransition metals metallic elements located

in Groups 3-12 of the periodic table

radioactive nuclei of the atoms are continually decaying to produce different elements

Nonmetals• include some elements in Groups 13-16 & all in Groups 17-18

Carbon is usually found as what, in its’ pure state?

NonmetalsThe most plentiful gases in the air are…

N & O Odorless yellow solid?

Halogens highly reactive elements located in Group 17 of the periodic table

Poisonous Poisonous yellow-green gas?yellow-green gas?

Cl is widely used to kill bacteria

NonmetalsI is used in table salt to prevent goiters from forming (enlarged thyroid gland)

Fl is used in some toothpastes & added to drinking water to help prevent tooth decay

Noble Gases unreactive gaseous elements located in Group 18 of the periodic table

Ne is responsible for…

Why are the noble gases so unreactive?

He is lighter than air & gives balloons lift

Ar prevents filaments from burning

Semiconductors Semiconductors (metalloids)

nonmetals exhibiting some metallic properties under certain circumstances

Silicon is the most familiar semiconductor, making up 28% of the earth’s crust

Electron OrbitalsOrbital a region in an atom where there is a high probability of

finding electrons

Four Orbital Types

Simplest…sshaped like a sphere

max 2 e-

pdumbbell-shaped

max 2 e-

/orbital (3)

max 2 e-

/orbital (5)

max 2 e- /orbital (7)

d

f

                                                                                   

                                                             

Energy Levels, Orbitals, and Electrons Energy Level # of Orbitals Max # of Electrons

1 1 2

2 4 8

3 9 18

4 16 32

Electron Orbitals

Question?

Atoms are mostly________?

A. Protons

B. Neutrons

C. Electrons

D. All of these

E. None of these

Answer

E. None of these

Atoms are 99.999% empty space, essentially a vacuum.

There is the nucleus and the electrons circling around it

Between the nucleus and circling electrons there is absolutely nothing!

The nucleus makes up 99.9% of the atom’s mass.

Facts

The radius of the electron cloud is 10,000 times larger than the nucleus of the atom

Even with this huge cloud, it contains almost none of the total mass of an atom

The volume of an atom is 1 trillion times larger than the nucleus