Modern Periodic TableSection 5.1 and 5.2

Periodic Law

• Dmitri Mendeleev – arranged elements into rows in order of increasing mass– Elements with similar properties are in

same column– Also predicted properties for

undiscovered elements

http://www.chem.msu.su/eng/misc/mendeleev/welcome.html

Mendeleev’s Periodic Table

Source: http://www.corrosionsource.com/handbook/periodic/

Periodic Table• An arrangement of elements in

columns, based on a set of properties that repeat from row to row

Periods

• A row in the table of elements (horizontal)• Period 1 = 2 elements (H and He)• Periods 2 & 3 = 8 elements each• # of elements per period varies b/c the

orbitals increase from energy level to energy level for electrons

• Orbitals = # beside the period (like 4 above)

Example• H (Hydrogen) has 1 electron• He (Helium) has 2 electrons• 1st energy level = 1 orbital

– Electrons of H and He fit this orbital• But Li (lithium) has 3 electrons

– 2 electrons fit in one orbital, but the third electron must be in the 2nd energy level

321641893842211

Maximum # of electrons

# of OrbitalsEnergy Level

Energy Levels, Orbitals & Electrons

321641893842211

Maximum # of electrons

# of OrbitalsEnergy Level

Energy Levels, Orbitals & Electrons

• This is why Li is the 1st element in Period 2– has 3 electrons, but 2 fit in one orbital, the

third must be in the 2nd orbital

• What about sodium (Na)?– 1 electron in 3rd energy level

• Potassium (K)?– 1 electron in 4th energy level

Groups• The columns on the periodic table• Elements within groups have

similar properties• Properties of elements repeat in a

predictable way when the atomic # are used to arrange elements in groups

Groups continued…• They have similar electron configurations

(arrangements)– The number at the top = valence electrons (all

elements in the group have the same number of valence electrons)

– This determines its chemical properties• Periodic law – pattern of repeating

properties displayed by elements in periodic table

• Look at the chart– How many groups: _____– How many periods: _____

Valence electrons• An electron that is

in the highest occupied energy level of an atom

• Elements in a group have similar properties because they have the same number of valence electrons

Quick Review of Isotopes• Atoms of the same element

that have different Neutrons (no charge) and different masses– But they still have the same

atomic #• Atomic mass units (amu) –

1/12 the mass of a C-12 atom (6 protons, 6 neutrons)

• In nature, most elements exist as a mixture of 2 or more isotopes

Example

• Chlorine (Cl)– Atomic #17– Mass of 35.453 amu– So where does this mass come from?

• 2 natural isotopes Chlorine-35 & Chlorine-37– Cl-35 has 17 pro, 18 neutrons– Cl-37 has 17 pro, 20 neutrons (this mass is >)

Metals• Some metals are extremely reactive

– Compare Au and (Mg) when exposed to air• Au shiny; Mg dulls

• Metals in “the middle” are transition metals– Bridge elements from left and right– form compounds with distinctive colors

• Good conductors of electricity and heat• Are solid at room temp (except Mercury)• Most are malleable and ductile

Nonmetals• Elements that are poor conductors

of heat and electric current• Have low boiling points, so many are

gases at room temp.– Fluorine (F) #9 is highly reactive

• F in toothpaste bonds with Na (sodium)

Metalloids• Elements with properties that fall between

metals and nonmetals• Ability to conduct electric current varies

with temp.– Ex) Silicon (Si) and Germanium (Ge) are good

insulators (retain heat) at low temp. but are good conductors (transfer heat) at high temp.

Germanium

Silicon

Variation Across A Period• States of matter

– Solid: black; liquid: blue; gas: red

• General properties– Metals (left)– Nonmetals (right)– Metalloids (in between)