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Modern Periodic Table(Section 5.2)

• The PERIODIC TABLE is an arrangement of elementsin columns, based on a set of properties that repeatfrom row to row

• Elements are arranged by increasing atomic number(# of protons)

Periods• A PERIOD is a row in the

table of elements• The number of elements

per period varies becausethe number of availableorbitals increases from oneenergy level to the next

Groups• A GROUP is a column on the periodic table• Properties repeat in a predictable way when atomic

numbers are used to arrange elements into groups• Elements in groups have similar electron configurations

and chemical properties• PERIODIC LAW is the pattern of repeating properties

Atomic Mass• Depends on the distribution of an element’s isotopes in

nature and the masses of those isotopes• ATOMIC MASS UNIT (amu) is defined as 1/12 the

mass of a Carbon-12 atom• Isotopes of chlorine

– Chlorine-35 occurs 75.78% naturally– Chlorine-37 occurs only 24.22% naturally– Therefore the atomic mass of chlorine is is the

WEIGHTED AVERAGE (35.453 and not 35)

Classes of Elements1. SOLID, LIQUID, or GAS

(based on their state atroom temperature)

2. NATURALLYOCCURING vs. NOTNATURALLYOCCURING

3. METAL, NONMETAL,METALLOID

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Metals• Good conductors of electric current

and heat• Solid at room temperature (except

mercury)• Malleable (can be pounded into

flat sheets) and ductile (drawninto thin wires)

• Some are extremely reactive andsome do not react easily

Transition Metals• Elements that form a

bridge between theelements on the leftand right sides of thetable

• Form compounds withdistinctive colors

Nonmetals• Poor conductors of heat and electric

current• Low boiling points, many are gases

at room temperature• All the gases in the periodic table are

nonmetals• The ones that are solid at room

temperature tend to be brittle• Some are extremely reactive, some

hardly react at all, and some fall inbetween

• Fluorine is the most reactivenonmetal

Metalloids• Properties that fallbetween those of metalsand nonmetals

• Ability to conductelectricity varies withtemperature

• Silicon and germaniumare good insulators atroom temperature andgood conductors at hightemperatures

Variation Across a Period• Across a period from left to right, the elements become

less metallic and more nonmetallic in their properties

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